Organic–inorganic metal halide perovskite solar cells represent the fastest advancing solar cell technology in terms of energy conversion efficiency improvement, as seen in the last decade. This has become a promising technology for next-generation, low-cost, high-efficiency photovoltaics including multi-junction tandem cell concepts. Double-junction tandem cells have much higher efficiency limits of 45%, beyond the Shockley–Queisser limits for a single-junction solar cell. In this review, recent progress with the perovskite tandem solar cells is highlighted, in particular, with 2-terminal perovskite–Si, perovskite–CIGS [where CIGS = Cu(In,Ga)(S,Se)2], perovskite–organic photovoltaic, perovskite–perovskite, and 3-junction-perovskite tandems. The opportunity and challenges of two-terminal monolithic perovskite tandems are discussed including a roadmap of strategies for further improving their efficiencies.

Crystalline silicon based solar cell technology currently dominates the commercial photovoltaic market due to its robustness in terms of manufacturing technology, product reliability, and low manufacturing costs, which have dropped significantly in the last decade fueling the exponential growth in global installations.1,2 However, the incumbent technology is based on a single-junction silicon solar cell, which inherently is limited in terms of power conversion efficiency (PCE). The maximum practical achievable limit is 29.4% when taking into account the Auger recombination in the silicon material.3,4 In the case when the bandgap of the single junction is unconstrained and there are no non-ideal losses, the theoretical limit under the standard AM1.5G illumination5 is 33.8%, which is far from 100%. The main contributors to this difference are sub-bandgap and thermalization losses. The former results from photons with energy less than the bandgap of the semiconductor in the single-junction solar cell that cannot be absorbed by creating electron-hole pairs and the latter from photons with energy exceeding the bandgap that are absorbed but with their excess energy dissipated as heat.

Multi-junction tandem solar cells involve the stacking of solar cells with different bandgaps (highest on the sun-facing side) allowing each cell to absorb different parts of the solar spectrum more efficiently, minimizing sub-bandgap and thermalization losses. Figures 1(a) and 1(b) illustrate two configurations for double-junction tandem cells. Figure 1(c) shows the reduction of sub-bandgap and thermalization losses as the number of junctions in a tandem stack increases. The theoretical efficiency limit of multi-junction also increases with the number of junctions from ∼45% for double junction to ∼51% for triple junction and to ∼55% for four-junction tandems as shown in Fig. 1(d).6 Multi-junction concepts have been implemented for III–V solar cells in the last few decades7 especially for space applications where the energy conversion efficiency is paramount, outweighing the cost.

FIG. 1.

Schematics of two types of two-junction tandem configurations: (a) Four-terminal (4T) mechanically stacked tandem and (b) two terminal (2T) monolithically integrated tandem. (c) Fundamental losses in solar cells as a function of the number of junctions under the AM1.5 solar spectrum.8 Reproduced with permission from L. C. Hirst and N. Ekins‐Daukes, Prog. Photovoltaics 19, 286 (2011). Copyright 2011 John Wiley and Sons, Inc. (d) Maximum efficiency for a bandgap value as part of a multi-junction solar cell stack for cases up to and including six band gaps under the air mass 1.5 global (AM1.5G) standard solar spectrum.6 Reproduced with permission from Bremner et al., Sol. Energy 135, 750 (2016). Copyright 2016 Elsevier.

FIG. 1.

Schematics of two types of two-junction tandem configurations: (a) Four-terminal (4T) mechanically stacked tandem and (b) two terminal (2T) monolithically integrated tandem. (c) Fundamental losses in solar cells as a function of the number of junctions under the AM1.5 solar spectrum.8 Reproduced with permission from L. C. Hirst and N. Ekins‐Daukes, Prog. Photovoltaics 19, 286 (2011). Copyright 2011 John Wiley and Sons, Inc. (d) Maximum efficiency for a bandgap value as part of a multi-junction solar cell stack for cases up to and including six band gaps under the air mass 1.5 global (AM1.5G) standard solar spectrum.6 Reproduced with permission from Bremner et al., Sol. Energy 135, 750 (2016). Copyright 2016 Elsevier.

Close modal

A double-junction tandem is the simplest implementation of the multi-junction approach. They can be realized by mechanically stacking the high-bandgap cell on top of the low-bandgap cell with the cells operating independently electrically. The total power is the sum of power generated by each cell. This approach involves the least integration effort, allowing cells to be fabricated and optimized independently at the expense of extra wiring and an insulating layer between the cells incurring extra cost. The insulating layer needs to be chosen to reduce the refractive index mismatch when interfacing with the cells9 in order to minimize the optical loss from Fresnel reflection. The transparent electrodes also need to have a sufficient lateral conductivity for independent cell operation but will inevitably introduce some level of optical transmission loss.

A monolithically integrated tandem represents the more elegant tandem approach, typically involving the fabrication of the high-bandgap cell directly on the low bandgap cell. This means that fabrication technologies for the top cell must be “bottom-cell compatible” so to not cause any damage during cell processing. The fabrication of interconnection layer(s) is also required but can be made ultra-thin as the layer or the stack is only responsible for vertical (not lateral) carrier transport. This can be via tunneling or recombination layers in the form of carrier selective layers, transparent conductive oxide (TCO), such as indium tin oxide (ITO) or ultra-thin metal.10,11 As the cells are electrically connected in series, the output voltage of the tandem will be the sum of the voltages of the individual cells. However, the current will be limited by the cell with the least output. This highlights the importance of the individual cell efficiencies for tandems. There is no incentive in stacking an under-performing high-bandgap cell on top of a high efficiency cell “poaching” valuable sunlight from it. Therefore, cell technologies chosen for tandems must be comparable, with similar efficiencies.

Hybrid metal halide perovskite solar cell technology12 [perovskite crystal structure shown in Fig. 2(a)] has recently emerged as a promising candidate for multi-junction tandems due to the rapid improvement in its power conversion efficiency (PCE) from 3.8% in 200913 to the recently certified 25.5% in 2020.7 The high performance is due to its high external radiative efficiency (ERE) comparable to those of Si and copper indium gallium selenide (CIGS) solar cell technologies.14 Perovskites have strong optical absorption meaning cells can be prepared as thin films and can be readily fabricated by solution processing. Bandgap can also be tuned (e.g., from 1.20 to 2.3 eV) via compositional engineering. All of these attributes make metal halide perovskites highly desirable for tandem cell applications. Most recently, reports of perovskite–Si,15 perovskite–CIGS,16 perovskite–perovskite,17 and perovskite–organic-photovoltaics (OPV) tandems18 have demonstrated promising energy conversion efficiencies.

FIG. 2.

(a) Cubic perovskite crystal structure.12 Reproduced with permission from Green et al., Nat. Photonics. 8, 506 (2014). Copyright 2014 Springer Nature. Efficiency limit of various perovskite-based double-junction monolithic tandems displayed (b) graphically and (c) listed in tabulated form.

FIG. 2.

(a) Cubic perovskite crystal structure.12 Reproduced with permission from Green et al., Nat. Photonics. 8, 506 (2014). Copyright 2014 Springer Nature. Efficiency limit of various perovskite-based double-junction monolithic tandems displayed (b) graphically and (c) listed in tabulated form.

Close modal

Figure 2(b) shows the efficiency potentials of double-junction perovskite-based tandem solar cells based on the Shockley–Queisser limit calculations assuming the bandgaps listed in the table in Fig. 2 for each subcell. The bandgaps of Si, CIGS, perovskite, and OPV bottom subcells are based on what has been demonstrated or feasible, especially for perovskite and OPV's.17,19 The top cell bandgaps are based on the best values that produce the highest tandem cell performance assuming 100% absorption and no non-ideal carrier-recombination in any of the subcells, showing above 40% energy conversion efficiencies are achievable. This shows the great potential for these tandem technologies to overcome the efficiency limits for single-junction cells.

As discussed above, monolithic tandem cells have the advantages of wiring simplicity, material savings, and reduced optical loss from a much thinner interconnection layer or stack between the subcells compared to the mechanically stacked tandem. Therefore, this review will focus on monolithic tandem designs, which are commercially attractive despite integration challenges, along with other general challenges associated with tandems using perovskite which will be discussed below. Figure 3 shows the reported and certified efficiencies of perovskite–Si, perovskite–CIGS, perovskite–perovskite, and perovskite–OPV tandems that can be found in published scientific journals or press releases.7,15–88 While the numbers are well below the theoretical limits (Fig. 2), the effectiveness of tandems using perovskites is clearly evident by the fact that tandem efficiencies of demonstrated perovskite–Si, perovskite–CIGS, and perovskite–OPV tandems have exceeded the efficiencies of demonstrated single-junction Si, CIGS, and OPV cells (Fig. 3) given that the first perovskite tandem cell demonstration was only in 2015. Past advancements made with these tandems will be reviewed in this article.

FIG. 3.

Two-terminal double-junction perovskite tandem solar cells. (a) Evolution of tandem cell energy conversion efficiencies reported. (b) JSC vs FF*VOC as a percentage of theoretical limits. Solid markers: independently certified results.7,15–84,88,89 (c) List of record efficiencies of perovskite tandem cells.

FIG. 3.

Two-terminal double-junction perovskite tandem solar cells. (a) Evolution of tandem cell energy conversion efficiencies reported. (b) JSC vs FF*VOC as a percentage of theoretical limits. Solid markers: independently certified results.7,15–84,88,89 (c) List of record efficiencies of perovskite tandem cells.

Close modal

Although, at this stage, only the perovskite–Si tandem cell has been demonstrated to exceed the demonstrated performance of single-junction perovskite cells, it is expected that perovskite–perovskite, perovskite–CIGS and perovskite–OPV tandem cells will follow suit in the near term. Challenges and outlook for further efficiency improvements for perovskite tandems will also be outlined in this article guiding future research.

As shown in Fig. 4 and Table I, a great progress has been made in the development of high-efficiency monolithic perovskite–Si tandem solar cells since 2015.

FIG. 4.

Two terminal perovskite–Si tandem solar cell. (a) Evolution of energy conversion efficiency. (b) JSC vs FF×VOC as a percentage of theoretical limits. (c) and (d) Different types of cell designs contrasting n-i-p vs p-i-n structures and contrasting homo-junction vs hetero-junction Si bottom cells.

FIG. 4.

Two terminal perovskite–Si tandem solar cell. (a) Evolution of energy conversion efficiency. (b) JSC vs FF×VOC as a percentage of theoretical limits. (c) and (d) Different types of cell designs contrasting n-i-p vs p-i-n structures and contrasting homo-junction vs hetero-junction Si bottom cells.

Close modal
TABLE I.

Demonstrated monolithic perovskite–Si tandems. MA = CH3NH3, FA = HC(NH2)2, SHJ = silicon heterojunction solar cells.

Lower-bandgap bottom cellInterfaceHigher-bandgap top cellVOC (V)JSC (mA/cm2)FF (%)Eff. (%)Area (cm2)Reference
Homo junction (p+ front emitter/n-Si/n++ rear BSF) n++Si mp-TiO2/MAPbI3/Spiro-OMeTAD/AgNW/LiF 1.58 11.5 75 13.7 1.0 22  
SHJ [a-Si(p) front/n-Si] ITO ALD SnO2/MAXFA1-XPbIYBr3-Y/Spiro-OMeTAD/MoOX/ITO/LiF 1.80 13.0 78 18.0 0.16 23  
SHJ (a-Si(p) front / n-Si) IZO PCBM/PEIE/MAPbI3/Spiro-OMeTAD/MoOX/ITO/IO:H/ARF 1.70 16.1 70 19.2 1.22 24  
1.69 15.9 78 21.2 0.17 
SHJ [a-Si(p) front/n-Si] IZO SnO2/PEIE/PCBM/MAPbI3/Spiro-OMeTAD/MoOX/IO:H/ITO 1.72 16.4 72 20.5a 1.43 25  
Homo junction (p+ front emitter/n-Si/n++ rear BSF) ZTO Sputtered c-TiO2/mp-TiO2/MAPbI3/Spiro-OMeTAD/MoOX/ITO/IO:H/ARF 1.64 15.3 65 16.3 1.43 26  
SHJ [a-Si(p) rear/n-Si] ITO NiO/FA0.83Cs0.17Pb(I0.83Br0.17)3/LiF/PC60BM/SnO2/ZTO/ITO/Ag/LiF 1.65 18.1 79 23.6b 0.99 85  
SHJ (a-Si(p) front / n-Si) nc-Si:H(p+)/nc-Si:H(n+) C60/Cs0.19MA0.81PbI3/Spiro-OMeTAD/MoOx/IZO/MgF2 1.75 16.8 77 22.0a 0.25 27  
1.78 16.5 74 21.2a 1.43 
1.77 16.5 65 18.0a 13.0 
Homo junction p+ front emitter/n-Si/n++ rear BSF) Al2O3/SiNX/ITO c-TiO2/mp-TiO2/Cs0.07Rb0.03FA0.765MA0.135PbI2.55Br0.45/Spiro-OMeTAD/MoOx/IZO/ARF 1.75 17.6 74 22.5a 1.0 28  
SHJ [a-Si(p) front/n-Si] ITO SnO2/MA0.37FA0.48Cs0.15PbI2.01Br0.99/Spiro-OMeTAD/MoOX/ITO/LiF 1.70 15.3 79 20.6 0.03 29  
Homo junction (p+ front emitter /n-Si/n++ rear PERL) None SnO2/MAPbI3/Spiro-OMeTAD/MoO3/ITO/ARF 1.68 16.1 78 20.5a 4.0 30  
1.69 15.6 68 17.1a 16.0 
SHJ [a-Si(p) rear/n-Si] nc-Si:H(n+)/nc-Si:H(p+) Spiro-TTB/CsXFA1-XPb(I,Br)3/LiF/C60/SnO2/IZO/Ag/MgF2 1.79 19.5 73 25.2a,b 1.42 31  
SHJ [a-Si(p) rear/n-Si] ITO PTAA/FA0.83Cs0.17Pb(I0.83Br0.17)3/C60/SnO2/ZTO/ITO/Ag/ PDMS 1.77 18.4 77 25.0 1.0 32  
Homo junction (p+ front emitter /n-Si/n++ rear PERL) None SnO2/(FAPbI3)0.83(MAPbI3)0.17/Spiro-OMeTAD/MoO3/ITO/ARF 1.74 16.2 78 21.8a 16.0 33  
SHJ [nc-SiOX:H(p) front/n-Si] ITO SnO2/MAFACsPbIBr/Spiro-OMeTAD/MoOX/ITO/ARC 1.78 17.8 75 22.8b 0.13 34  
SHJ [a-Si(p) front/n-Si] ITO SnO2/FA0.5MA0.38Cs0.12PbI2.04Br0.96/Spiro-OMeTAD/MoOX/ITO 1.66 16.5 81 22.2 0.06 35  
SHJ [a-Si(p) rear/n-Si] ITO PTAA/Cs0.15(FA0.83MA0.17)0.85Pb(I0.8Br0.2)3/ICBA/C60/SnO2/IZO/Cu/MgF2 1.80 17.8 79 25.4 0.42 36  
SHJ [a-Si(p) rear/n-Si/nc-SiOx:H(n) FSF] ITO PTAA/Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3/ICBA/C60/SnO2/IZO/Ag/PDMS 1.76 18.5 78 25.5 0.77 37  
1.80 19.8 79 28.0b 1.03 88  
SHJ [nc-SiOX:H(p) front/n-Si] ITO SnO2/MAFACsPbIBr/Spiro-OMeTAD/MoOX/ITO/Au/PDMS 1.75 16.9 74 21.9 0.13 40  
SHJ [poly-Si (p+) front/n-Si] None c-TiO2/mp-TiO2/ PMMA/PCBM/Cs0.05Rb0.05FA0.765MA0.135PbI2.55Br0.45/PTAA for SHJ or Spiro-OMeTAD for homo junction Si/MoOX/IZO/Au/PDMS 1.76 17.8 78 24.5 1.0 41  
Homo junction (p+ front emitter/n-Si/n+ rear BSF) None 1.70 17.2 79 22.9a 1.0 
SHJ [a-Si(p) rear/n-Si] ITO SnO2/MAFACsPbIBr/Spiro-OMeTAD/MoOX/ITO/Au 1.83 16.0 70 20.4 0.13 42  
SHJ [nc-SiOX:H(n) front/n-Si] ITO F4-TCNQ:polyTPD/ Cs0.05(FA0.83MA0.17)0.95Pb(I1-xBrx)3/ETL/Buffer/ITO/Ag /ARC 1.79 19.0 75 25.2b 1.0 43  
SHJ [nc-SiC(n) front/SiOX/p-Si] nc-Si:H (p+) Spiro-TTB/CsFAPbIBr/LiF/C60/SnO2/IZO/Ag/MgF2 1.74 19.5 75 25.1 1.42 44  
Homo junction (n+ front emitter/p-Si/rear Al-BSF) ITO PTAA/(FAPbI3)0.8(MAPbBr3)0.2/PCBM/ZnO/IZO)/Ag/LiF 1.65 16.1 80 21.2 0.27 45  
SHJ [a-Si(p) rear/n-Si] ITO NiO/Cs0.17FA0.83PbI0.83Br0.17/C60/SnO2/ITO/Ag/MgF2 1.72 17.5 75 22.6 57.4 46  
SHJ (a-Si(p) rear / n-Si) ITO PTAA/Cs0.05(MA0.83FA0.17)Pb(I0.83Br0.17)3/C60/SnO2/IZO/Ag/LiF 1.77 19.2 77 26.0 0.77 47  
1.78 17.8 78 25.0 0.77 
Homo junction (p+ front emitter/n-Si/n++ rear PERL) None SnO2/(FAPbI3)0.83(MAPbI3)0.17/Spiro-OMeTAD/MoO3/ITO/Ag/(Ba,Sr)2SiO4:Eu2+:PDMS 1.73 16.5 81 23.0a 4.0 92  
SHJ [a-Si(p) front/n-Si] ITO TiO2/mp-TiO2/PCBM:PMMA/FA0.75Cs0.25Pb(I0.8Br0.2)3/Spiro-OMeTAD/ITO/MgF2 1.84 15.3 77 21.6a 0.249 49  
SHJ [a-Si(p+) rear/n-Si] ITO PTAA/Cs0.1MA0.9Pb(I0.9Br0.1)3/C60/SnO2/ITO/Ag/PDMS 1.82 19.2 75 26.1a 0.42 50  
SHJ [a-Si(p+) rear/n-Si] InOX NiOX/Cs0.05MA0.15FA0.8PbI2.25Br0.75/LiF/C60/SnO2/IZO/Ag/MgF2 1.78 19.0 75 25.7b 0.832 51  
SHJ (a-Si(p+) rear/ n-Si) ITO NiOX/Poly-TPD/PFN/CsxFA1-xPbIyBr1-y+MAPbCl3/LiF/C60/SnO2/ZTO/IZO/Ag/PDMS 1.87 19.1 75 27.0a 1.0 52  
1.87 18.3 80 25.8b 1.0 
SHJ [a-Si(p+) rear/n-Si] ITO PTAA/PEA(I0.25SCN0.75):FA0.65MA0.20Cs0.15Pb(I0.8Br0.2)3/C60/PEIE/ITO/Ag 1.82 18.9 76 26.2b 1.001 53  
SHJ [a-Si(p+) rear/n-Si] ITO PTAA/PFN/ FA0.75Cs0.25Pb(I0.8Br0.2)3/C60/SnOx/ITO/MgF2 1.77 17.7 80 25.1b 0.25 54  
SHJ [a-Si(p+) rear/n-Si/a-Si(i)/a-Si:H(n)] ITO NiOx/PTAA/(MAPb(I0.75Br0.25)3/C60/SnO2/IZO/MgF2 1.76 19.2 70 24.1a 1.0 55  
SHJ [a-Si(p+) rear/n-Si/a-Si(i)/nc-SiOx(n)] Nc-Si:H(n+)/Spiro-TTB Spiro-TTB/FACsMAPbI3–xBrx/C60/SnO2/IZO 1.73 19.8 73 25.1 1.0 56  
SHJ [a-Si(p+) rear/n-Si/a-Si(i)/nc-SiOx(n)] ITO PTAA(or SAM)/ Cs0.05(FA0.77MA0.23)0.95Pb(I0.77Br0.23)3/LiF/ C60/SnO2/IZO/LiF 1.90 19.3 79 29.2b 1.06 15  
1.88 20.26 77 29.5b 1.212 100  
SHJ [a-Si(p+) rear/n-Si/a-Si:H(i)/nc-Si(n)] ITO NiOx/FACsMAPbI3–xBrx/C60/SnO2/IZO/MgF2 1.80 18.5 76 25.2b 0.832 57  
SHJ [a-Si(p+) rear/n-Si(CZ)/a-Si(i)/nc-SiOx(n)] ITO 2PACz/Cs0.05(FA0.77MA0.23)0.95 Pb(I0.77Br0.23)3/LiF/C60/SnO2/IZO/LiF 1.94 17.8 81 27.9 1.0 86  
SHJ [a-Si(p+) rear/n-Si/a-Si(i)/a-Si:H(n)] ITO SAM/Cs0.15MA0.15FA0.70Pb(I0.80Br0.20)3/C60/SnO2/IZO/MgF2 1.84 19.6 76 27.4 1.03 87  
Lower-bandgap bottom cellInterfaceHigher-bandgap top cellVOC (V)JSC (mA/cm2)FF (%)Eff. (%)Area (cm2)Reference
Homo junction (p+ front emitter/n-Si/n++ rear BSF) n++Si mp-TiO2/MAPbI3/Spiro-OMeTAD/AgNW/LiF 1.58 11.5 75 13.7 1.0 22  
SHJ [a-Si(p) front/n-Si] ITO ALD SnO2/MAXFA1-XPbIYBr3-Y/Spiro-OMeTAD/MoOX/ITO/LiF 1.80 13.0 78 18.0 0.16 23  
SHJ (a-Si(p) front / n-Si) IZO PCBM/PEIE/MAPbI3/Spiro-OMeTAD/MoOX/ITO/IO:H/ARF 1.70 16.1 70 19.2 1.22 24  
1.69 15.9 78 21.2 0.17 
SHJ [a-Si(p) front/n-Si] IZO SnO2/PEIE/PCBM/MAPbI3/Spiro-OMeTAD/MoOX/IO:H/ITO 1.72 16.4 72 20.5a 1.43 25  
Homo junction (p+ front emitter/n-Si/n++ rear BSF) ZTO Sputtered c-TiO2/mp-TiO2/MAPbI3/Spiro-OMeTAD/MoOX/ITO/IO:H/ARF 1.64 15.3 65 16.3 1.43 26  
SHJ [a-Si(p) rear/n-Si] ITO NiO/FA0.83Cs0.17Pb(I0.83Br0.17)3/LiF/PC60BM/SnO2/ZTO/ITO/Ag/LiF 1.65 18.1 79 23.6b 0.99 85  
SHJ (a-Si(p) front / n-Si) nc-Si:H(p+)/nc-Si:H(n+) C60/Cs0.19MA0.81PbI3/Spiro-OMeTAD/MoOx/IZO/MgF2 1.75 16.8 77 22.0a 0.25 27  
1.78 16.5 74 21.2a 1.43 
1.77 16.5 65 18.0a 13.0 
Homo junction p+ front emitter/n-Si/n++ rear BSF) Al2O3/SiNX/ITO c-TiO2/mp-TiO2/Cs0.07Rb0.03FA0.765MA0.135PbI2.55Br0.45/Spiro-OMeTAD/MoOx/IZO/ARF 1.75 17.6 74 22.5a 1.0 28  
SHJ [a-Si(p) front/n-Si] ITO SnO2/MA0.37FA0.48Cs0.15PbI2.01Br0.99/Spiro-OMeTAD/MoOX/ITO/LiF 1.70 15.3 79 20.6 0.03 29  
Homo junction (p+ front emitter /n-Si/n++ rear PERL) None SnO2/MAPbI3/Spiro-OMeTAD/MoO3/ITO/ARF 1.68 16.1 78 20.5a 4.0 30  
1.69 15.6 68 17.1a 16.0 
SHJ [a-Si(p) rear/n-Si] nc-Si:H(n+)/nc-Si:H(p+) Spiro-TTB/CsXFA1-XPb(I,Br)3/LiF/C60/SnO2/IZO/Ag/MgF2 1.79 19.5 73 25.2a,b 1.42 31  
SHJ [a-Si(p) rear/n-Si] ITO PTAA/FA0.83Cs0.17Pb(I0.83Br0.17)3/C60/SnO2/ZTO/ITO/Ag/ PDMS 1.77 18.4 77 25.0 1.0 32  
Homo junction (p+ front emitter /n-Si/n++ rear PERL) None SnO2/(FAPbI3)0.83(MAPbI3)0.17/Spiro-OMeTAD/MoO3/ITO/ARF 1.74 16.2 78 21.8a 16.0 33  
SHJ [nc-SiOX:H(p) front/n-Si] ITO SnO2/MAFACsPbIBr/Spiro-OMeTAD/MoOX/ITO/ARC 1.78 17.8 75 22.8b 0.13 34  
SHJ [a-Si(p) front/n-Si] ITO SnO2/FA0.5MA0.38Cs0.12PbI2.04Br0.96/Spiro-OMeTAD/MoOX/ITO 1.66 16.5 81 22.2 0.06 35  
SHJ [a-Si(p) rear/n-Si] ITO PTAA/Cs0.15(FA0.83MA0.17)0.85Pb(I0.8Br0.2)3/ICBA/C60/SnO2/IZO/Cu/MgF2 1.80 17.8 79 25.4 0.42 36  
SHJ [a-Si(p) rear/n-Si/nc-SiOx:H(n) FSF] ITO PTAA/Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3/ICBA/C60/SnO2/IZO/Ag/PDMS 1.76 18.5 78 25.5 0.77 37  
1.80 19.8 79 28.0b 1.03 88  
SHJ [nc-SiOX:H(p) front/n-Si] ITO SnO2/MAFACsPbIBr/Spiro-OMeTAD/MoOX/ITO/Au/PDMS 1.75 16.9 74 21.9 0.13 40  
SHJ [poly-Si (p+) front/n-Si] None c-TiO2/mp-TiO2/ PMMA/PCBM/Cs0.05Rb0.05FA0.765MA0.135PbI2.55Br0.45/PTAA for SHJ or Spiro-OMeTAD for homo junction Si/MoOX/IZO/Au/PDMS 1.76 17.8 78 24.5 1.0 41  
Homo junction (p+ front emitter/n-Si/n+ rear BSF) None 1.70 17.2 79 22.9a 1.0 
SHJ [a-Si(p) rear/n-Si] ITO SnO2/MAFACsPbIBr/Spiro-OMeTAD/MoOX/ITO/Au 1.83 16.0 70 20.4 0.13 42  
SHJ [nc-SiOX:H(n) front/n-Si] ITO F4-TCNQ:polyTPD/ Cs0.05(FA0.83MA0.17)0.95Pb(I1-xBrx)3/ETL/Buffer/ITO/Ag /ARC 1.79 19.0 75 25.2b 1.0 43  
SHJ [nc-SiC(n) front/SiOX/p-Si] nc-Si:H (p+) Spiro-TTB/CsFAPbIBr/LiF/C60/SnO2/IZO/Ag/MgF2 1.74 19.5 75 25.1 1.42 44  
Homo junction (n+ front emitter/p-Si/rear Al-BSF) ITO PTAA/(FAPbI3)0.8(MAPbBr3)0.2/PCBM/ZnO/IZO)/Ag/LiF 1.65 16.1 80 21.2 0.27 45  
SHJ [a-Si(p) rear/n-Si] ITO NiO/Cs0.17FA0.83PbI0.83Br0.17/C60/SnO2/ITO/Ag/MgF2 1.72 17.5 75 22.6 57.4 46  
SHJ (a-Si(p) rear / n-Si) ITO PTAA/Cs0.05(MA0.83FA0.17)Pb(I0.83Br0.17)3/C60/SnO2/IZO/Ag/LiF 1.77 19.2 77 26.0 0.77 47  
1.78 17.8 78 25.0 0.77 
Homo junction (p+ front emitter/n-Si/n++ rear PERL) None SnO2/(FAPbI3)0.83(MAPbI3)0.17/Spiro-OMeTAD/MoO3/ITO/Ag/(Ba,Sr)2SiO4:Eu2+:PDMS 1.73 16.5 81 23.0a 4.0 92  
SHJ [a-Si(p) front/n-Si] ITO TiO2/mp-TiO2/PCBM:PMMA/FA0.75Cs0.25Pb(I0.8Br0.2)3/Spiro-OMeTAD/ITO/MgF2 1.84 15.3 77 21.6a 0.249 49  
SHJ [a-Si(p+) rear/n-Si] ITO PTAA/Cs0.1MA0.9Pb(I0.9Br0.1)3/C60/SnO2/ITO/Ag/PDMS 1.82 19.2 75 26.1a 0.42 50  
SHJ [a-Si(p+) rear/n-Si] InOX NiOX/Cs0.05MA0.15FA0.8PbI2.25Br0.75/LiF/C60/SnO2/IZO/Ag/MgF2 1.78 19.0 75 25.7b 0.832 51  
SHJ (a-Si(p+) rear/ n-Si) ITO NiOX/Poly-TPD/PFN/CsxFA1-xPbIyBr1-y+MAPbCl3/LiF/C60/SnO2/ZTO/IZO/Ag/PDMS 1.87 19.1 75 27.0a 1.0 52  
1.87 18.3 80 25.8b 1.0 
SHJ [a-Si(p+) rear/n-Si] ITO PTAA/PEA(I0.25SCN0.75):FA0.65MA0.20Cs0.15Pb(I0.8Br0.2)3/C60/PEIE/ITO/Ag 1.82 18.9 76 26.2b 1.001 53  
SHJ [a-Si(p+) rear/n-Si] ITO PTAA/PFN/ FA0.75Cs0.25Pb(I0.8Br0.2)3/C60/SnOx/ITO/MgF2 1.77 17.7 80 25.1b 0.25 54  
SHJ [a-Si(p+) rear/n-Si/a-Si(i)/a-Si:H(n)] ITO NiOx/PTAA/(MAPb(I0.75Br0.25)3/C60/SnO2/IZO/MgF2 1.76 19.2 70 24.1a 1.0 55  
SHJ [a-Si(p+) rear/n-Si/a-Si(i)/nc-SiOx(n)] Nc-Si:H(n+)/Spiro-TTB Spiro-TTB/FACsMAPbI3–xBrx/C60/SnO2/IZO 1.73 19.8 73 25.1 1.0 56  
SHJ [a-Si(p+) rear/n-Si/a-Si(i)/nc-SiOx(n)] ITO PTAA(or SAM)/ Cs0.05(FA0.77MA0.23)0.95Pb(I0.77Br0.23)3/LiF/ C60/SnO2/IZO/LiF 1.90 19.3 79 29.2b 1.06 15  
1.88 20.26 77 29.5b 1.212 100  
SHJ [a-Si(p+) rear/n-Si/a-Si:H(i)/nc-Si(n)] ITO NiOx/FACsMAPbI3–xBrx/C60/SnO2/IZO/MgF2 1.80 18.5 76 25.2b 0.832 57  
SHJ [a-Si(p+) rear/n-Si(CZ)/a-Si(i)/nc-SiOx(n)] ITO 2PACz/Cs0.05(FA0.77MA0.23)0.95 Pb(I0.77Br0.23)3/LiF/C60/SnO2/IZO/LiF 1.94 17.8 81 27.9 1.0 86  
SHJ [a-Si(p+) rear/n-Si/a-Si(i)/a-Si:H(n)] ITO SAM/Cs0.15MA0.15FA0.70Pb(I0.80Br0.20)3/C60/SnO2/IZO/MgF2 1.84 19.6 76 27.4 1.03 87  
a

Steady-state.

b

Certified or independently verified.

TABLE II.

Demonstrated monolithic perovskite–CIGS tandems.

Lower bandgapInterfaceHigher bandgapVOC (V)JSC (mA/cm2)FF (%)Eff. (%)Area (cm2)Reference
Glass/Si3N3/Mo/CIGSa/CdS (1.04 eV) ITO PEDOT:PSS/MAPbIXBr3-X/PCBM/Al (1.7 eV) 1.45 12.7 56.6 10.9 0.4 58  
Glass/Mo/CIGSb/CdS/i-ZnO/BZO (1.1 eV) ITO PTAA/Cs0.09FA0.77MA0.14Pb(I0.86Br0.14)3/PCBM/ZnO NPs/ITO (1.59 eV) 1.77 17.3 73.1 22.4c 0.042 16  
Glass/Mo/CIGSed/i-ZnO (1.1 eV) AZO NiOx/PTAA/CsMAFAPbIBr/C60/SnO2/IZO (1.63 eV) 1.58 18.0 76.0 21.6 0.778 59  
Polyimide substrate/Mo/CIGSd/CdS/i-ZnO (1.1 eV) i-ZnO/AZO (ZnO:Al) PTAA/CH3NH3PbI3/PCBM/ZnO NP/AZO/Ni-Al grid/MgF2 (1.57 eV) 1.75 16.3 46.4 13.2 0.201 61  
Glass/Mo/CIGSed/i-ZnO (1.1 eV) AZO MeO-2PACz/Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3/C60/BCP/ITO/Cu or Ag grid/NaF (1.63 eV) 1.68 19.2 71.9 23.3c 1.04 60  
Glass/Mo/NaF/CIGSd/CdS/i-ZnO (1.1 eV) AZO NiO/FA0.83Cs0.17Pb(I0.83Br0.17)3/LiF/PC60BM/SnO2/ITO/LiF (1.63 eV) 1.77 14.7 70.0 15.9 0.12 62  
Glass/Mo/CIGSed/i-ZnO (1.1 eV) AZO SAM/PEAI:Cs0.05(MA0.23FA0.77)Pb1.1(I0.77Br0.23)3/LiF/C60/SnO2/ITO/Cu or Ag grid/NaF (1.66 eV) 1.77 19.2 72.9 24.2c 1.045 103  
Lower bandgapInterfaceHigher bandgapVOC (V)JSC (mA/cm2)FF (%)Eff. (%)Area (cm2)Reference
Glass/Si3N3/Mo/CIGSa/CdS (1.04 eV) ITO PEDOT:PSS/MAPbIXBr3-X/PCBM/Al (1.7 eV) 1.45 12.7 56.6 10.9 0.4 58  
Glass/Mo/CIGSb/CdS/i-ZnO/BZO (1.1 eV) ITO PTAA/Cs0.09FA0.77MA0.14Pb(I0.86Br0.14)3/PCBM/ZnO NPs/ITO (1.59 eV) 1.77 17.3 73.1 22.4c 0.042 16  
Glass/Mo/CIGSed/i-ZnO (1.1 eV) AZO NiOx/PTAA/CsMAFAPbIBr/C60/SnO2/IZO (1.63 eV) 1.58 18.0 76.0 21.6 0.778 59  
Polyimide substrate/Mo/CIGSd/CdS/i-ZnO (1.1 eV) i-ZnO/AZO (ZnO:Al) PTAA/CH3NH3PbI3/PCBM/ZnO NP/AZO/Ni-Al grid/MgF2 (1.57 eV) 1.75 16.3 46.4 13.2 0.201 61  
Glass/Mo/CIGSed/i-ZnO (1.1 eV) AZO MeO-2PACz/Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3/C60/BCP/ITO/Cu or Ag grid/NaF (1.63 eV) 1.68 19.2 71.9 23.3c 1.04 60  
Glass/Mo/NaF/CIGSd/CdS/i-ZnO (1.1 eV) AZO NiO/FA0.83Cs0.17Pb(I0.83Br0.17)3/LiF/PC60BM/SnO2/ITO/LiF (1.63 eV) 1.77 14.7 70.0 15.9 0.12 62  
Glass/Mo/CIGSed/i-ZnO (1.1 eV) AZO SAM/PEAI:Cs0.05(MA0.23FA0.77)Pb1.1(I0.77Br0.23)3/LiF/C60/SnO2/ITO/Cu or Ag grid/NaF (1.66 eV) 1.77 19.2 72.9 24.2c 1.045 103  
a

Solution processed.

b

Sputtered.

c

Certified or independently verified.

d

Evaporation.

e

Steady-state.

Mailoa et al.22 reported the first demonstration of monolithic perovskite–Si tandem in 2015 using homo-junction Si as the bottom cell, a mesoscopic perovskite top cell with a n++ tunneling junction layer for the integrating the two cells. The champion cell achieved a 13.7% PCE on 1 cm2 with a VOC of 1.65 V. The first demonstration of monolithic perovskite–Si tandem using a heterojunction silicon bottom cell as the bottom cell was reported by Albrecht et al.23 in late 2015. The champion cell achieved a PCE of 18% and VOC of 1.78V. Since then, heterojunction Si cells have been widely used as the bottom cells for laboratory demonstrations (Table I) due to the readily available indium tin oxide (ITO) for top and bottom cell integration and demonstrated high open voltage and therefore efficiency. Nevertheless, homo-junction Si cells especially of PERC or PERL type (where “PE” standards for passivated emitter, “RC” standards for rear contacts, and “RL” standards for rear localized contacts), as bottom cell choice are industrially relevant, since of lower cost than heterojunction Si cells90 while also having high efficiency, providing an immediate pathway for commercializing perovskite–Si tandems. Due to the absence of an amorphous Si layer found in heterojunction cells, homo-junction cells can withstand higher processing temperature during subsequent perovskite cell fabrication. Relatively few perovskite–Si-homo-junction-cell tandem demonstrations have been reported to date (Table I), meaning there is scope for improvement, such as in further optimization of the front emitter of the Si bottom cell allowing for heavier doping. This is not possible for single-junction Si cells without jeopardizing blue light response, which is no longer absorbed by the Si bottom cell in a tandem but by the perovskite top cell. Other approaches for further improving the efficiencies of Si bottom cells can also be investigated.20,91 The lower output current (halved in a two junction) in a tandem also means that previous design restrictions can be relaxed due to lower resistive losses.

In terms of the interface layer between the perovskite and Si subcells, ITO with a thickness of 40–120 nm (Refs. 23, 28, 29, 34, 35, 42, 45, 49, and 54) is typically used in earlier works. Thinner layers [e.g., 10–20 nm (Refs. 15, 32, 36, 37, 46, 47, 50, 53, and 85)] result in less parasitic absorption and optical loss. Zinc tin oxide (ZTO), nanocrystalline silicon (nc-Si), and nanocrystalline silicon oxide interlayers are just as effective or even better optically as reported by Werner et al. in 2016,26 Sahli et al. in 2017,27 and Mazzarella et al. in 2019,43 respectively. In fact, work by Zheng et al.30,33,92 and Shen et al.41 demonstrated that transparent conductive oxide, such as ITO, is not a prerequisite for interfacing top and bottom cells in perovskite–Si-homo-junction tandems. They showed that both solution-processed SnO2 and TiO2 deposited by atomic layer deposition (ALD) can act as electron transport layers for the perovskite top cell as well as recombination layers for the perovskite–Si interface. Zheng et al.30,92 found that their interface-TCO-free tandems are suitable for large area cells which have a very narrow distribution of fill factor values. This is due to the limited lateral conductivity (otherwise present in TCO) in the SnO2 layer thereby localizing any undesirable shunting related effects. A similar effect using nanocrystalline Si as a recombination junction with poor lateral conductivity for localizing shunting is also reported by Sahli et al.27 Integration approaches suitable for PERC or PERL cells are also suitable for newer type of homo-junction cells with poly-Si with tunnel oxide passivated contacts.41 

In terms of cell polarity, the n-i-p structure (where “n” is at the bottom and “p” is at the top sun facing side) has been the most popular in the early stages of tandem cell development due to the proven process for perovskite cell fabrication where the electron transport layer (e.g., TiO2 of SnO2) is fabricated first and hole transport layer (HTL) such as 2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD) is fabricated after perovskite deposition. However, spiro-OMeTAD has a very high parasitic absorption and the presence of MoO3 (necessary for protecting the spiro-OMeTAD and the underlying layers from damage caused by sputtering which is typically used to deposit the top transparent conductive oxide electrode) causes Fresnel reflection and therefore optical losses.30 One way of circumventing this is to replace the spiro-OMeTAD layer with a less absorptive layer although, so far, with little successes (Table I). Another way is to apply down-shifting material on the top surface of the cell, e.g., attaching a thin polydimethylsiloxane (PDMS) layer incorporated with (Ba,Sr)2SiO4:Eu2+.92 Ultra violet (UV) light that is typically absorbed by the spiro-OMeTAD layer is downshifted to wavelengths absorbable by the perovskite layer for electrical energy generation. The p-i-n structure (where “p” is at the bottom and “n” is at the top sun facing side) has been shown to overcome the short comings of the n-i-p structure for perovskite–Si tandems. The first tandem demonstration with such a polarity was reported by Bush et al.85 in 2017. The champion cell had a relatively high JSC of 18.1 mA/cm2 at the time reporting and achieved a certified efficiency of 23.6%. The typical hole transport layer, which is fabricated before the deposition of perovskite absorber in a p-i-n perovskite cell, is typically NiOx or poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) (Table I). The electron-hole transport layer stack (on top of the perovskite absorber) in a p-i-n perovskite cell is typically (LiF)/C60/ALD SnO2 in perovskite–Si15,25,32,36,37,43–45,50–52,54–57 and in perovskite–CIGS59,60 tandem solar cells.

In terms of maximizing the current output, MgF227 and LiF85 can be applied onto the top of the tandem cell to reduce reflection. Si, as an indirect bandgap semiconductor, has a lower absorption coefficient than perovskites12 requiring light trapping for maximizing optical path length for light absorption, especially for the long-wavelength light. Texturing is effective in this regard. One way of achieving this is to apply a textured coating such as a textured thin PDMS on the top surface of a perovskite–Si tandem cell. The advantage of using PDMS is that it is relatively easy to control its thickness (to sub-millimeter92) to incorporate luminescent materials, such as downshifters for optical management30 and to mold its surface to replicate different kinds of texturing, such as pyramidal40 or rose petal surface.30JSC in the range of 15.6–18.4 mA/cm2 has been achieved using this approach.30,32,37,40

Another way to achieve texturing is to texture the Si cell surface directly, which is routinely done for commercial Si cells. The advantage of this approach is that mass-produced Si cells are ready to be used for tandems without altering standard manufacturing processes. However, textured surface poses a challenge to perovskite solar cell fabrication where a conformal coating is desired93 (Fig. 5). The first work that overcame this challenge was reported by Sahli et al.31 in 2018 who used a two-step sequential deposition method (PbI2 evaporation and MAI solution spin coating) to fabricate a conformal perovskite layer. The champion cell achieved a certified efficiency of 25.2% and JSC of 19.5 mA/cm2 for 1.42 cm2 area. More recently, three works50,51,55 have further demonstrated the viability of solution processing for achieving full coverage of perovskite over textured Si surface (where the troughs of the texture are filled) especially when the texture feature size is reduced down to ∼1 μm. These processing methods include blade coating,50 spin coating,51 and slot-die-coating55 (Fig. 5), and tandem cells demonstrated were 26.1%, 25.7% (certified), and 24.1%, efficient, respectively, with JSC in the range of 19.0–19.2 mA/cm2.

FIG. 5.

Conformal or full coverage perovskite on textured Si surface achieved by (a) two-step sequential deposition method: Pb2 evaporation followed by MAI solution spin coating;31 Reproduced with permission from Sahli et al., Nat. Mater. 17, 820 (2018). Copyright 2014 Springer Nature. (b) Blade coating;50 Reproduced with permission from Chen et al., Joule 4, 850 (2020). Copyright 2020 Elsevier. (c) Spin coating;51 Reproduced with permission from Hou et al., Science 367, 1135 (2020). Copyright 2020 American Association for the Advancement of Science, and (d) slot-die-coating;55 Reproduced with permission from Subbiah et al., ACS Energy Lett. 5, 3034 (2020). Copyright 2020 American Chemical Society.

FIG. 5.

Conformal or full coverage perovskite on textured Si surface achieved by (a) two-step sequential deposition method: Pb2 evaporation followed by MAI solution spin coating;31 Reproduced with permission from Sahli et al., Nat. Mater. 17, 820 (2018). Copyright 2014 Springer Nature. (b) Blade coating;50 Reproduced with permission from Chen et al., Joule 4, 850 (2020). Copyright 2020 Elsevier. (c) Spin coating;51 Reproduced with permission from Hou et al., Science 367, 1135 (2020). Copyright 2020 American Association for the Advancement of Science, and (d) slot-die-coating;55 Reproduced with permission from Subbiah et al., ACS Energy Lett. 5, 3034 (2020). Copyright 2020 American Chemical Society.

Close modal

Another consideration in terms of the optical performance of tandem cells is the change in solar spectrum content during the day and throughout the year. This causes individual cells to produce less than ideal current output under “non-ideal” or “non-standard” illumination conditions especially when the spectrum is “red-rich” or “blue-rich” depending on the diffuse-direct sunlight composition. The underperforming subcell will limit the output current of the other cell in the tandem due to the cells being connected in series in a two-terminal monolithic configuration. This effect has been modeled by M. T. Hörantner and H. J. Snaith,94 and the conclusion is that the efficiency of the tandem cell is not significantly “de-rated” by real-world spectral variations. Furthermore, it is possible to optimize tandem solar cell stacks for a specific location for maximizing energy yield and therefore levelized cost of electricity.

Recently, outdoor testing of two terminal perovskite–Si tandem solar cell has been conducted by Aydin et al.56 They found that it was not the spectral content but the temperature dependence of both the silicon and perovskite bandgaps that impacted current performance. The bandgap of Si bottom cell drops with the increasing temperature due to the increased energy of the electrons and weakened interatomic bonds95 at elevated temperature. This is typical for tetrahedrally coordinated semiconductors as well.96 However, perovskites have an opposite trend—the bandgap increases with temperature.96 This is due to the antibonding nature of the highest energy valence band states [e.g., Pb(6s)/I(5p) for MAPbI3].97 These opposite trends in terms of bandgaps for the top and bottom cells mean tandems that are optimized at standard test conditions do not necessarily produce matched current outputs in the field. Aydin et al. recommended the use of perovskites with bandgap smaller than 1.68 eV favoring bromide-lean perovskites as the top cell choice for field conditions where operational temperatures are higher than 55 °C.

In terms of future improvements, it is clear that JSC of the state-of-the-art perovskite–Si tandem cells have already reached very high values—90% of the theoretical limit at 21.6 mA/cm2 [Fig. 4(b)]. However, there is still room for improvement especially for large area cells, given the growing interest (with a 13 cm2 tandem reported in 2017,27 a 16 cm2 tandem reported in 201830,92 and a 57 cm2 reported in 201946 as well as the 6-in. square tandem mentioned in a 2018 press release88) This will require a better metal grid design to minimize shading33 and the development of scalable deposition method (a move away from spin coating), not just for high-quality large-area perovskite films33,98,99 but also for uniform transport and interface layers.

While it is encouraging that the record efficiency of perovskite–Si tandem at 29.5% (certified) has surpassed the record efficiency of Si single-junction cell at 26.7% (certified) (Fig. 6), it is clear that VOC and FF of demonstrated tandems still lag behind their single-junction counterparts. The products of VOC and FF of perovskite–Si tandem cells are at most 70% of the theoretical limit [Fig. 4(b)] while VOC ×FF of the best single-junction Si cell and the best (1.52 eV) single-junction perovskite cells are between 80% and 90% [Fig. 3(b)]. This is because the FF of tandem cells are still less than ideal. Only 5 out of 38 perovskite–Si tandem cells demonstrated have FF ≥ 80% indicating a room for improvement especially with the interfacing of the subcells. In terms of VOC, the success of tandems relies heavily on the voltage output of the top higher-bandgap cell (Table in Fig. 2) as the voltage output of the lower-bandgap cell has less scope for further improvement. Later in this review under Sec. II F, we will review the progress of high-bandgap perovskite solar cells and opportunities for further improvement—critical to the success of perovskite multi-junction tandems.

FIG. 6.

(a) Cell structure, (b) current density–voltage curve, and (c) external quantum efficiency of record monolithic perovskite–Si tandem.15 Reproduced with permission from Al-Ashouri et al., Science 370, 1300 (2020). Copyright 2020 American Association for the Advancement of Science.

FIG. 6.

(a) Cell structure, (b) current density–voltage curve, and (c) external quantum efficiency of record monolithic perovskite–Si tandem.15 Reproduced with permission from Al-Ashouri et al., Science 370, 1300 (2020). Copyright 2020 American Association for the Advancement of Science.

Close modal

CIGS is a well-established thin-film photovoltaic technology. While the CIGS bandgap is tunable, the state-of-the-art cells already have a bandgap of 1.08 eV,21 which is suitably low for them to act as bottom cells for perovskite tandems. Aligning with the standard polarity of a typical CIGS cell,101 p-i-n cell structure is normally required for the perovskite top cell in a tandem [Fig. 7(c)]. The first demonstration of monolithic perovskite–CIGS tandem was reported by Todorov et al.102 in 2015 [Fig. 7(a)]. The CIGS cell was fabricated by a solution process such that its bandgap could be tuned to 1.04 eV and the perovskite top cell was fabricated by a vapor-assisted process with in situ monitoring such that its bandgap could be tuned [Fig. 8(a)]. ZnO, which is typically part of a CIGS cell, was removed, which was believed to be the cause of perovskite instability. The champion cell achieved a PCE of 10.9% and VOC of 1.45 V. However, it is clear that the bottom CIGS cell performance was inferior, thereby limiting the performance of the tandem.

FIG. 7.

Two terminal perovskite–CIGS tandem solar cell. (a) Evolution of energy conversion efficiency. (b) JSC vs FF× VOC as a percentage of theoretical limits. (c) Cell design options.

FIG. 7.

Two terminal perovskite–CIGS tandem solar cell. (a) Evolution of energy conversion efficiency. (b) JSC vs FF× VOC as a percentage of theoretical limits. (c) Cell design options.

Close modal
FIG. 8.

Various fabrication methods and cell designs for achieving perovskite–CIGS monolithic tandem solar cell. (a) Perovskite fabricated by vapor-assisted process on solution processed CIGS.58 Reproduced with permission from Todorov et al., Adv. Energy Mater. 5, 1500799 (2015). Copyright 2015 John Wiley and Sons, Inc. (b) Chemical mechanical polish to achieve smooth bottom CIGS cell for top perovskite cell fabrication.16 Reproduced with permission from Han et al., Science 361, 904 (2018). Copyright 2018 American Association for the Advancement of Science. (c) Bilayer NiOx/PTAA hole transport layer design to achieve conformal coating and efficient charge transport.59 Reproduced with permission from Jost et al., ACS Energy Lett. 4, 583 (2019). Copyright 2019 American Chemical Society. (d) Solution processed self-assembling monolayers as hole transport layer without requiring ALD to achieve conformal coating.60 Reproduced with permission from Al-Ashouri et al., Energy Environ. Sci. 12, 3356 (2019). Copyright 2019 Author(s), licensed under a Creative Commons Attribution 3.0 Unported License.

FIG. 8.

Various fabrication methods and cell designs for achieving perovskite–CIGS monolithic tandem solar cell. (a) Perovskite fabricated by vapor-assisted process on solution processed CIGS.58 Reproduced with permission from Todorov et al., Adv. Energy Mater. 5, 1500799 (2015). Copyright 2015 John Wiley and Sons, Inc. (b) Chemical mechanical polish to achieve smooth bottom CIGS cell for top perovskite cell fabrication.16 Reproduced with permission from Han et al., Science 361, 904 (2018). Copyright 2018 American Association for the Advancement of Science. (c) Bilayer NiOx/PTAA hole transport layer design to achieve conformal coating and efficient charge transport.59 Reproduced with permission from Jost et al., ACS Energy Lett. 4, 583 (2019). Copyright 2019 American Chemical Society. (d) Solution processed self-assembling monolayers as hole transport layer without requiring ALD to achieve conformal coating.60 Reproduced with permission from Al-Ashouri et al., Energy Environ. Sci. 12, 3356 (2019). Copyright 2019 Author(s), licensed under a Creative Commons Attribution 3.0 Unported License.

Close modal

After a long gap of 3 years, Han et al.16 in 2018 reported a certified 22.4% efficient perovskite–CIGS tandem with some cell design improvements. First of all, the ZnO in the CIGS cell was reinstated. While the long-term cell stability is an ongoing research focus, the cells were stable enough for certification measurements. Second, CIGS by physical deposition was used for the bottom cell which produced higher performance, with a trade-off of film roughness hindering subsequent perovskite cell fabrication. This problem was overcome by chemical mechanical polishing of the ITO layer that capped the BZO/CIGS cell [Fig. 8(b)]. The ITO layer was deposited to be intentionally thick (300 nm) and then polished down to 40 nm without significantly jeopardizing cell efficiency (decreased from 18.7% to 16.8%). However, polishing is a costly process for commercial production.

In early 2019, Jost et al.59 from Albrecht's group reported a perovskite top cell design that is compatible with rough CIGS cell surfaces without requiring polishing. The perovskite top cell utilized a NiOx/PTAA bilayer as the hole transport layer. The NiOx layer deposited by ALD forms a conformal coating on the CIGS cell and therefore prevents shunting. Instead of a 300 °C post anneal to improve NiOx conductivity (which will adversely affect the CIGSe cell performance due to inter-diffusion at the CIGSe/CdS interface), a PTAA layer is deposited to aid the carrier transport [Fig. 8(c)]. A 21.6% stead-state efficiency was achieved on 0.8 cm2 area. In the second half of 2019, Al-Ashouri et al.60 also from Albrecht's group further improved the perovskite cell design focusing on the hole transport layer that is solution processed without the need for ALD. In their work, self-assembling monolayers (SAMs) in the form MeO-2PACz were synthesized and deposited either by spin coating (multiple times) or dip coating to form a conformal coating on the ZnO-capped rough CIGS bottom cell [Fig. 8(d)]. The champion CIGS-perovskite tandem device produced a certified efficiency 23.3% on 1 cm2 area. The major performance improvement came from high current output.

In early 2020, Jost et al. from the same group63 reported a new certified record efficiency of perovskite–CIGS tandem with 24.2% efficiency. While the cell structure was essentially unchanged from that last reported by Al-Ashouri et al.,40 PEAI was incorporated into the Cs0.05(MA0.23FA0.77)Pb1.1(I0.77Br0.23)3 perovskite and 1 nm LiF was deposited onto the perovskite layer to reduce interface recombination, producing a high VOC value of 1.77 V. Another interesting work by Fu et al.61 involved a proof-of-concept of a flexible perovskite–CIGS tandem on 30 μm polyimide foil with an efficiency of 13.2% and VOC of 1.75 V. Further work has been suggested by the authors to improve efficiency further by thickening the perovskite absorber layer (to >280 nm), replacing MAPbI3 with more stable CsFA mixed perovskites, replacing AZO with ITO to increase the thermal budget allowed during annealing, and replacing spin-coated electron/hole selective layers by vacuum-deposited counterparts without sacrificing the device performance.

Given that there were only seven perovskite–CIGS tandem demonstrations compared to 41 for perovskite–Si tandems, the pace of development for the former has been extraordinary [Fig. 7(b)]. Nevertheless, there is ample scope and motivation of further development due to the thin film advantages of perovskite–CIGS tandems, such as flexibility, solution processability, and bandgap tunability compared to the perovskite–Si tandem counterparts.

Moving forward, it is important to understand the challenges posed by the CIGS bottom cell. First, similar to the Si-heterojunction bottom cell with a TCO layer, the CIGS bottom cell can only withstand processing temperature below 200 °C. Second, the surface roughness of the CIGS cell is severe and irregular. Third, the polarity of CIGS cell limits the structure allowable for the perovskite cell. This means that developing a low-temperature processing for high-efficiency, high-bandgap p-i-n perovskite solar cells with conformal and full coverage on rough and irregular surfaces is critical to the success of perovskite–CIGS tandems.

Looking at the performance of the current state of the art perovskite–CIGS tandems, JSC is still below 90% of the theoretical limit, necessitating a thorough optical analysis of the state-of-the-art perovskite–CIGS tandem cells. This is to identify key optical losses and new cell designs for minimizing front reflection, Fresnel reflection, parasitic absorptions in interlayers and maximizing optical absorption by the CIGS and perovskite absorber layers. An approach that can improve the latter is by applying a back reflector, doubling the optical path length through the cells, which is present in Si solar cells and in single-junction perovskite solar cell. In terms of FF × VOC, the value is only 60% of its theoretical limit for perovskite–CIGS tandems compared to 70% for perovskite–Si tandems, necessitating improvements in cell design for better charge carrier management, such as the development of interface layer to enhance charge transport and surface passivation. There is also scope for further improving the performance of the CIGS cell, especially the quality of the rear surface passivation. Many of the CIGS cells used in tandem demonstrations have shown to have less than ideal external quantum efficiency (EQE) at long wavelength, e.g., at 1000 nm. This needs to be improved and is critically important as the CIGS cell will be solely responsible for long-wavelength absorption in a tandem.

Recently, there have been some interest in the demonstration of perovskite–OPV tandems (Fig. 9 and Table III) building on the advances in the improved stability and efficiency particularly from the recent emergence of non-fullerene acceptor for OPV.104,105 OPV is also a solution processable technology and is advantageous when a non-polar solvent [e.g., chlorobenzene (CBZ)] is used for its fabrication, posing minimal damage to the perovskite cell which is fabricated first in a superstrate configuration. Therefore, the perovskite–OPV tandem is amenable to roll-to-roll manufacturing for flexible applications.84 The first perovskite–OPV tandem demonstration was reported by Chen et al.82 in 2015. While the order of the junctions is somewhat back-to-front with the lower-bandgap PBSeDTEG8:PCBM OPV cell being illuminated first followed by the higher-bandgap CH3NH3PbI3, the team reported a 10.2% efficient tandem cell. Recent demonstrations18,19 have been successful in terms of boosting the efficiencies to above what can be achieved by OPV cell alone (>18.2%7).

FIG. 9.

Two terminal perovskite–OPV tandem solar cell: (a) evolution of energy conversion efficiency and (b) JSC vs FF × VOC as a percentage of theoretical limits.

FIG. 9.

Two terminal perovskite–OPV tandem solar cell: (a) evolution of energy conversion efficiency and (b) JSC vs FF × VOC as a percentage of theoretical limits.

Close modal
TABLE III.

Demonstrated monolithic perovskite–OPV tandems.

Top cellInterfaceBottom cellVOC (V)JSC (mA/cm2)FF (%)Eff. (%)Area (cm2)Reference
ITO/PEDOT:PSS/PBSeDTEG8:PCBM/PFN/TiO2 (1.28 eV) PEDOT:PSS PH500/ CH3NH3PbI3/PCBM/PFN/Al (1.51 eV) 1.52 10.1 67 10.2 0.1 82  
PEDOT:PSS4083 
ITO/PEDOT:PSS/ CH3NH3PbI3/PC61BM (1.55 eV) C60-SB/Ag/MoO3 PCE-10: PC71BM /C60-N/Ag (1.64 eV) 1.63 13.1 75 16.0 0.055 83  
ITO/PTAA/Cs0.1(FA0.6MA0.4)0.9Pb(I0.6Br0.4)3/PCBM/BCP (1.74 eV) Ag M-PEDOT/PBDB-T:SN6IC4F/Bis-C60/BCP/Ag (1.30 eV) 1.85 11.5 71 15.1 0.13 84  
ITO/NiOx/FA0.8MA0.02Cs0.18PbI1.8Br1.2/C60 (1.77 eV) BCP/Ag nanoparticle/MoOx PBDBT-2F:Y6:PC71BM (1:1.2:0.2) (1.41 eV) 1.90 13.1 83 20.6 0.062 18  
1.91 12.2 78 19.5a 0.062 
ITO/ZnO/SnO2/CsPbI2Br/PDCBT/ (1.9 eV) MoO3/Ag/ZnO PM6:Y6-based/MoO3/Ag (1.37 eV) 1.95 12.5 76 18.4 0.04 19  
PTB7-Th:O6T-4F/MoO3/Ag (1.28 eV) 1.86 12.9 75 18.0 0.04 
Top cellInterfaceBottom cellVOC (V)JSC (mA/cm2)FF (%)Eff. (%)Area (cm2)Reference
ITO/PEDOT:PSS/PBSeDTEG8:PCBM/PFN/TiO2 (1.28 eV) PEDOT:PSS PH500/ CH3NH3PbI3/PCBM/PFN/Al (1.51 eV) 1.52 10.1 67 10.2 0.1 82  
PEDOT:PSS4083 
ITO/PEDOT:PSS/ CH3NH3PbI3/PC61BM (1.55 eV) C60-SB/Ag/MoO3 PCE-10: PC71BM /C60-N/Ag (1.64 eV) 1.63 13.1 75 16.0 0.055 83  
ITO/PTAA/Cs0.1(FA0.6MA0.4)0.9Pb(I0.6Br0.4)3/PCBM/BCP (1.74 eV) Ag M-PEDOT/PBDB-T:SN6IC4F/Bis-C60/BCP/Ag (1.30 eV) 1.85 11.5 71 15.1 0.13 84  
ITO/NiOx/FA0.8MA0.02Cs0.18PbI1.8Br1.2/C60 (1.77 eV) BCP/Ag nanoparticle/MoOx PBDBT-2F:Y6:PC71BM (1:1.2:0.2) (1.41 eV) 1.90 13.1 83 20.6 0.062 18  
1.91 12.2 78 19.5a 0.062 
ITO/ZnO/SnO2/CsPbI2Br/PDCBT/ (1.9 eV) MoO3/Ag/ZnO PM6:Y6-based/MoO3/Ag (1.37 eV) 1.95 12.5 76 18.4 0.04 19  
PTB7-Th:O6T-4F/MoO3/Ag (1.28 eV) 1.86 12.9 75 18.0 0.04 
a

Independently verified.

TABLE IV.

Demonstrated monolithic perovskite–perovskite tandems. FSIP = Fluoride silane-incorporated polyethylenimine ethoxylated hybrid system.

Higher-bandgap bottom cellInterfaceLower-bandgap top cellVOC (V)JSC (mA/cm2)FF (%)Eff. (%)Area (cm2)Reference
Glass/FTO/c-TiO2/m-TiO2/MAPbI3/spiro-OMeTAD (1.55 eV) PEDOT:PSS PEI/PCBM:PEI/MAPbI3/spiro-OMeTAD/Ag (1.55 eV) 1.89 6.61 56 7.0 0.1 64  
Glass/FTO/bl-TiO2/MAPbBr3 (2.25 eV) wet P3HT PCBM/MAPbI3/PEDOT:PSS/ITO/Glass (1.55 eV) 1.95 8.4 66 10.8 0.096 65  
wet PTAA 2.25 8.3 56 10.4 0.096 
Glass/ITO/NiO/FA0.83Cs0.17Pb(I0.5Br0.5)3/PCBM/SnO2/ZTO (1.8 eV) ITO PEDOT:PSS/FA0.75Cs0.25Sn0.5Pb0.5I3/C60/BCP/Ag (1.2 eV) 1.66 14.5 70 17.0 0.2 66  
Glass/ITO/TiO2/IPH/Cs0.15FA0.85Pb(I0.3Br0.7)3/TaTm/TaTm:F6:TCNNQ (2.0 eV) C60:PhIm C60/MAPbI3/TaTm/TaTm:F6:TCNNQ/Au (1.55 eV) 2.14 9.7 76 15.6 0.026 67  
Glass/ITO/NiOx/MA0.9Cs0.1Pb(I0.6Br0.4)3/C60/Bis-C60 (1.82 eV) ITO PEDOT:PSS/MAPb0.5Sn0.5I3/IC60BA/Bis-C60/Ag (1.22 eV) 1.98 12.7 73 18.5 0.1 68  
Glass/FTO/c-TiO2/m-TiO2/MAPbBr3/spiro-OMeTAD (2.25 eV) PEDOT:PSS C60/MAPbI3/spiro-OMeTAD/Au (1.55 eV) 1.96 6.4 41 5.1 0.16 111  
Glass/ITO/PTAA/FA0.6Cs0.4Pb(I0.7Br0.3)/C60/ZTO (1.76 eV) ITO PEDOT:PSS/FA0.75Cs0.25Sn0.5Pb0.5I3/C60/BCP/Ag (1.25 eV) 1.81 14.8 72 19.1 ⋯ 69  
Glass/ITO/TiO2/C60/MAPbI3/TaTm/TaTm:F6:TCNNQ (1.55 eV) C60:PhIm C60/MAPbI3/TaTm/TaTm:F6:TCNNQ/Au (1.55 eV) 2.30 9.84 80 18.0 0.12 70  
Glass/ITO/NiOX/FA0.83Cs0.17Pb(Br0.5I0.5)3/FSIP/C60/BCP (1.83 eV) Cu/Au PEDOT:PSS/FA0.5MA0.5Pb0.5Sn0.5I3/polystyrene/C60/BCP/Ag (1.24 eV) 1.72 12.8 73 16.1 0.034 71  
Glass/ITO/TiOX/PC61BM/MAPbI3/Mo(tfdCOCF3)3 doped TPE-MN3 cross-linked PTAA/ (1.55 eV)  HMB-doped PC61BM/MASn0.25Pb0.75I3/Spiro-OMeTAD/Ag (1.25 eV) 1.79 13.4 78 18.7 0.12 72  
Glass/ITO/F4-TCNQ doped PTAA/FA0.8Cs0.2Pb(I0.7Br0.3)3/C60/BCP (1.75 eV) Ag/MoOX/ITO PEDOT:PSS/(FASnI3)0.6(MAPbI3)0.4:Cl/ C60/BCP/Ag (1.26 eV) 1.92 14.0 78 21.0 0.105 73  
Glass/ITO/PTAA/Cs0.05FA0.8MA0.15PbI2.55Br0.45/C60/SnOX/ZTO (1.75 eV) IZO PEDOT:PSS/GuaSCN:(FASnI3)0.6(MAPbI3)0.4/C60/ BCP/Ag (1.25 eV) 1.94 15.0 80 23.4 0.059 74  
Glass/ITO/PolyTPD/PFN-Br/ FA0.6Cs0.3DMA0.1PbI2.4Br0.6/LiF/C60/ PEIE (1.70 eV) AZO/IZO PEDOT:PSS/FA0.75Cs0.25Sn0.5Pb0.5I3/C60/BCP/Ag (1.27 eV) 1.88 16.0 77 23.1 0.058 75  
1.82 15.6 75 21.3 0.058 
Glass /ITO/ PTAA/FA0.8Cs0.2Pb(I0.6Br0.4)3/C60 (1.77 eV) SnO2/Au PEDOT:PSS/PTAA/Cd:FA0.5MA0.45Cs0.05Sn0.5Pb0.5I3/C60/BCP/Cu (1.22 eV) 1.93 15.8 81 24.8a 0.048 17  
1.95 14.0 82 22.3 1.05 
Glass/ITO/PTAA/FA0.6Cs0.4Pb(I0.65Br0.35)3/C60/SnO2 (1.80 eV) ITO PEDOT:PSS/PTAA/Cd:FA0.5MA0.45Cs0.05Sn0.5Pb0.5I3/C60/BCP/Cu (1.22 eV) 1.95 15.0 76 22.7 0.068 76  
Glass/ITO/PTAA/FA0.8Cs0.2PbI1.8Br1.2/C60 (1.77 eV) SnO2/Au PEDOT:PSS/PEAI:Cs0.1MA0.2FA0.7Pb0.5Sn0.5I3/C60/BCP/Ag (1.25 eV) 1.97 15.0 80 23.7 0.049 77  
Glass/ITO/PTAA/FA0.8Cs0.2Pb(I0.7Br0.3)3/C60/BCP (1.75 eV) ITO PEDOT:PSS/(FASnI3)0.6(MAPbI3)0.4/C60/BCP/Ag (1.25 eV) 1.91 14.1 79 21.1 0.12 78  
Glass/ITO/NiO/VNPB/FA0.8Cs0.2Pb(I0.6Br0.4)3/C60 (1.77 eV) SnO2/Au PEDOT:PSS/FSA:MA0.3FA0.7Pb0.5Sn0.5I3/C60/BCP/Cu (1.22 eV) 2.01 16.0 80 25.6 0.049 80  
1.99 15.9 77 24.2a 1.04 
1.96 14.8 74 21.4 12 
Glass/ITO/PTAA/Cs0.4FA0.6PbI1.95Br1.05(1.78 eV) C60/SnO1.76 Cs0.05MA0.45FA0.5Pb0.5Sn0.5I3/C60/BCP/Cu (1.25 eV) 2.03 15.2 80 24.6 0.059 79  
2.01 15.5 79 22.2 1.05 
Glass/ITO/PTAA/FA0.85MA0.1Cs0.05Sn0.5Pb0.5I3/C60 /BCP (1.73 eV) ITO PEDOT:PSS/(FASnI3)0.6(MAPbI3)0.4 /C60/BCP/Cu (1.28 eV) 1.94 15.1 79 23.3 0.12 81  
2.00 15.2 80 24.4a 0.049 89  
2.05 16.5 78 26.4a 0.049 100  
Higher-bandgap bottom cellInterfaceLower-bandgap top cellVOC (V)JSC (mA/cm2)FF (%)Eff. (%)Area (cm2)Reference
Glass/FTO/c-TiO2/m-TiO2/MAPbI3/spiro-OMeTAD (1.55 eV) PEDOT:PSS PEI/PCBM:PEI/MAPbI3/spiro-OMeTAD/Ag (1.55 eV) 1.89 6.61 56 7.0 0.1 64  
Glass/FTO/bl-TiO2/MAPbBr3 (2.25 eV) wet P3HT PCBM/MAPbI3/PEDOT:PSS/ITO/Glass (1.55 eV) 1.95 8.4 66 10.8 0.096 65  
wet PTAA 2.25 8.3 56 10.4 0.096 
Glass/ITO/NiO/FA0.83Cs0.17Pb(I0.5Br0.5)3/PCBM/SnO2/ZTO (1.8 eV) ITO PEDOT:PSS/FA0.75Cs0.25Sn0.5Pb0.5I3/C60/BCP/Ag (1.2 eV) 1.66 14.5 70 17.0 0.2 66  
Glass/ITO/TiO2/IPH/Cs0.15FA0.85Pb(I0.3Br0.7)3/TaTm/TaTm:F6:TCNNQ (2.0 eV) C60:PhIm C60/MAPbI3/TaTm/TaTm:F6:TCNNQ/Au (1.55 eV) 2.14 9.7 76 15.6 0.026 67  
Glass/ITO/NiOx/MA0.9Cs0.1Pb(I0.6Br0.4)3/C60/Bis-C60 (1.82 eV) ITO PEDOT:PSS/MAPb0.5Sn0.5I3/IC60BA/Bis-C60/Ag (1.22 eV) 1.98 12.7 73 18.5 0.1 68  
Glass/FTO/c-TiO2/m-TiO2/MAPbBr3/spiro-OMeTAD (2.25 eV) PEDOT:PSS C60/MAPbI3/spiro-OMeTAD/Au (1.55 eV) 1.96 6.4 41 5.1 0.16 111  
Glass/ITO/PTAA/FA0.6Cs0.4Pb(I0.7Br0.3)/C60/ZTO (1.76 eV) ITO PEDOT:PSS/FA0.75Cs0.25Sn0.5Pb0.5I3/C60/BCP/Ag (1.25 eV) 1.81 14.8 72 19.1 ⋯ 69  
Glass/ITO/TiO2/C60/MAPbI3/TaTm/TaTm:F6:TCNNQ (1.55 eV) C60:PhIm C60/MAPbI3/TaTm/TaTm:F6:TCNNQ/Au (1.55 eV) 2.30 9.84 80 18.0 0.12 70  
Glass/ITO/NiOX/FA0.83Cs0.17Pb(Br0.5I0.5)3/FSIP/C60/BCP (1.83 eV) Cu/Au PEDOT:PSS/FA0.5MA0.5Pb0.5Sn0.5I3/polystyrene/C60/BCP/Ag (1.24 eV) 1.72 12.8 73 16.1 0.034 71  
Glass/ITO/TiOX/PC61BM/MAPbI3/Mo(tfdCOCF3)3 doped TPE-MN3 cross-linked PTAA/ (1.55 eV)  HMB-doped PC61BM/MASn0.25Pb0.75I3/Spiro-OMeTAD/Ag (1.25 eV) 1.79 13.4 78 18.7 0.12 72  
Glass/ITO/F4-TCNQ doped PTAA/FA0.8Cs0.2Pb(I0.7Br0.3)3/C60/BCP (1.75 eV) Ag/MoOX/ITO PEDOT:PSS/(FASnI3)0.6(MAPbI3)0.4:Cl/ C60/BCP/Ag (1.26 eV) 1.92 14.0 78 21.0 0.105 73  
Glass/ITO/PTAA/Cs0.05FA0.8MA0.15PbI2.55Br0.45/C60/SnOX/ZTO (1.75 eV) IZO PEDOT:PSS/GuaSCN:(FASnI3)0.6(MAPbI3)0.4/C60/ BCP/Ag (1.25 eV) 1.94 15.0 80 23.4 0.059 74  
Glass/ITO/PolyTPD/PFN-Br/ FA0.6Cs0.3DMA0.1PbI2.4Br0.6/LiF/C60/ PEIE (1.70 eV) AZO/IZO PEDOT:PSS/FA0.75Cs0.25Sn0.5Pb0.5I3/C60/BCP/Ag (1.27 eV) 1.88 16.0 77 23.1 0.058 75  
1.82 15.6 75 21.3 0.058 
Glass /ITO/ PTAA/FA0.8Cs0.2Pb(I0.6Br0.4)3/C60 (1.77 eV) SnO2/Au PEDOT:PSS/PTAA/Cd:FA0.5MA0.45Cs0.05Sn0.5Pb0.5I3/C60/BCP/Cu (1.22 eV) 1.93 15.8 81 24.8a 0.048 17  
1.95 14.0 82 22.3 1.05 
Glass/ITO/PTAA/FA0.6Cs0.4Pb(I0.65Br0.35)3/C60/SnO2 (1.80 eV) ITO PEDOT:PSS/PTAA/Cd:FA0.5MA0.45Cs0.05Sn0.5Pb0.5I3/C60/BCP/Cu (1.22 eV) 1.95 15.0 76 22.7 0.068 76  
Glass/ITO/PTAA/FA0.8Cs0.2PbI1.8Br1.2/C60 (1.77 eV) SnO2/Au PEDOT:PSS/PEAI:Cs0.1MA0.2FA0.7Pb0.5Sn0.5I3/C60/BCP/Ag (1.25 eV) 1.97 15.0 80 23.7 0.049 77  
Glass/ITO/PTAA/FA0.8Cs0.2Pb(I0.7Br0.3)3/C60/BCP (1.75 eV) ITO PEDOT:PSS/(FASnI3)0.6(MAPbI3)0.4/C60/BCP/Ag (1.25 eV) 1.91 14.1 79 21.1 0.12 78  
Glass/ITO/NiO/VNPB/FA0.8Cs0.2Pb(I0.6Br0.4)3/C60 (1.77 eV) SnO2/Au PEDOT:PSS/FSA:MA0.3FA0.7Pb0.5Sn0.5I3/C60/BCP/Cu (1.22 eV) 2.01 16.0 80 25.6 0.049 80  
1.99 15.9 77 24.2a 1.04 
1.96 14.8 74 21.4 12 
Glass/ITO/PTAA/Cs0.4FA0.6PbI1.95Br1.05(1.78 eV) C60/SnO1.76 Cs0.05MA0.45FA0.5Pb0.5Sn0.5I3/C60/BCP/Cu (1.25 eV) 2.03 15.2 80 24.6 0.059 79  
2.01 15.5 79 22.2 1.05 
Glass/ITO/PTAA/FA0.85MA0.1Cs0.05Sn0.5Pb0.5I3/C60 /BCP (1.73 eV) ITO PEDOT:PSS/(FASnI3)0.6(MAPbI3)0.4 /C60/BCP/Cu (1.28 eV) 1.94 15.1 79 23.3 0.12 81  
2.00 15.2 80 24.4a 0.049 89  
2.05 16.5 78 26.4a 0.049 100  
a

Certified or independently verified.

b

Steady-state.

TABLE V.

Demonstrated 3-junction monolithic perovskite tandems.

Higher bandgapInterfaceMiddle bandgapInterfaceLower bandgapVOC (V)JSC (mA/cm2)FF (%)Eff. (%)Area (cm2)Reference
Glass/FTO/SnO2/FA0.83Cs0.17Pb(Br0.7I0.3)3/Spiro-OMeTAD (1.94 eV) PEDOT:PSS/ITO NPs PC61BM/MAPbI3/Spiro-OMeTAD (1.57 eV) PEDOT:PSS/ITO NPs PC61BM/MAPb0.75Sn0.25I3/Spiro-(TFSI)2/Ag (1.34 eV) 2.7 8.3 43 6.7 0.091 9 112  
Glass/ITO/PTAA/Cs0.2FA0.8PbI0.9Br2.1/C60 (1.99 eV) ALD-SnO2/Au NiO/PTAA/Cs0.05FA0.95PbI2.55Br0.45/C60 (1.60 eV) ALD-SnO2/Au PEDOT:PSS/MA0.3FA0.7Pb0.5Sn0.5I3/C60/BCP/Cu (1.22 eV) 2.80 8.8 81 20.1 0.049 113  
Glass/ITO/PTAA/Cs0.1(FA0.66MA0.34)0.9PbI2Br/C60 (1.73 eV) ALD-SnO2/Au PEDOT:PSS/PTAA/FA0.66MA0.34PbI2.85Br0.15/C60 (1.57 eV) ALD-SnO2/Au FA0.66MA0.34Pb0.5Sn0.5I3/C60/BCP/Ag (1.23 eV) 2.78 7.4 81 16.8 0.066 7 114  
MgF2/IZO/SnO2/C60/LiF/CsFAPbIBr/NiO (1.8 eV) IZO SnO2/C60/LiF/CsFAPbIBr/spiro-TTB (1.53 eV) nc-Si:H(p+)/nc-Si:H(n+) SHJ [a-Si(n) front/n-Si] (1.1 eV) 2.69 7.7 68 14.0 1.42 115  
Higher bandgapInterfaceMiddle bandgapInterfaceLower bandgapVOC (V)JSC (mA/cm2)FF (%)Eff. (%)Area (cm2)Reference
Glass/FTO/SnO2/FA0.83Cs0.17Pb(Br0.7I0.3)3/Spiro-OMeTAD (1.94 eV) PEDOT:PSS/ITO NPs PC61BM/MAPbI3/Spiro-OMeTAD (1.57 eV) PEDOT:PSS/ITO NPs PC61BM/MAPb0.75Sn0.25I3/Spiro-(TFSI)2/Ag (1.34 eV) 2.7 8.3 43 6.7 0.091 9 112  
Glass/ITO/PTAA/Cs0.2FA0.8PbI0.9Br2.1/C60 (1.99 eV) ALD-SnO2/Au NiO/PTAA/Cs0.05FA0.95PbI2.55Br0.45/C60 (1.60 eV) ALD-SnO2/Au PEDOT:PSS/MA0.3FA0.7Pb0.5Sn0.5I3/C60/BCP/Cu (1.22 eV) 2.80 8.8 81 20.1 0.049 113  
Glass/ITO/PTAA/Cs0.1(FA0.66MA0.34)0.9PbI2Br/C60 (1.73 eV) ALD-SnO2/Au PEDOT:PSS/PTAA/FA0.66MA0.34PbI2.85Br0.15/C60 (1.57 eV) ALD-SnO2/Au FA0.66MA0.34Pb0.5Sn0.5I3/C60/BCP/Ag (1.23 eV) 2.78 7.4 81 16.8 0.066 7 114  
MgF2/IZO/SnO2/C60/LiF/CsFAPbIBr/NiO (1.8 eV) IZO SnO2/C60/LiF/CsFAPbIBr/spiro-TTB (1.53 eV) nc-Si:H(p+)/nc-Si:H(n+) SHJ [a-Si(n) front/n-Si] (1.1 eV) 2.69 7.7 68 14.0 1.42 115  

However, the tandem efficiencies are still well below their theoretical limit (<50%) and lower than other perovskite tandem technologies [Fig. 3(c)]. This is because JSC is below 80% of the theoretical limit. The tandem JSC is limited by the bottom OPV cell as seen in the tandem external quantum efficiency curves.18,19 Moving forward, an optical analysis identifying key optical losses for current and new cell designs will be useful. In terms of FF × VOC, the best value is around 60% of its theoretical limit. Again, this necessitates improvements in cell designs especially the interface layers which currently limit cell performance, as seen in the poorer EQE in the top cell near its absorption edge. Nevertheless, the pace of perovskite–OPV tandem development is extraordinary given that there have only been four demonstrations thus far, signaling ample scope and motivation of further development.

The perovskite–perovskite tandem is a sensible pathway for low-cost, high-efficiency solar cells, as top and bottom cells share similar trajectories in terms of cell efficiency improvements, similar sensitivities to environmental stresses and therefore the same cell encapsulation and packaging requirements. The processing of top and bottom cells can also share similar infrastructure thereby lowering the capital expenditure. Figure 10 shows typical monolithic perovskite–perovskite tandem cell designs. Although both polarities have been demonstrated, the p-i-n cell structure is more favored.

FIG. 10.

Two terminal perovskite–perovskite tandem solar cell: (a) evolution of energy conversion efficiency, (b) JSC vs FF × VOC as a percentage of theoretical limits, and (c) and (d) different types cell designs and associated challenges.

FIG. 10.

Two terminal perovskite–perovskite tandem solar cell: (a) evolution of energy conversion efficiency, (b) JSC vs FF × VOC as a percentage of theoretical limits, and (c) and (d) different types cell designs and associated challenges.

Close modal

The two most common challenges associated with the demonstration of 2-terminal perovskite–perovskite tandem is (i) the demonstration of high-efficiency low-bandgap typically Sn–Pb perovskite cells, and (ii) the development of interfacing between the top and bottom cell to minimize damage to the bottom cell during the processing of the top cell, to minimize the interface recombination and to maximize the carrier transport between the subcells.

After the first “proof-of-concept” demonstrations using perovskites with non-ideal bandgaps, e.g., 1.5–1.5 (Ref. 64) and 2.25–1.5 eV,65 a two-terminal perovskite–perovskite tandem using a low-bandgap (1.2 eV) Sn-containing perovskite for the bottom cell was demonstrated by Eperon et al.66 in 2016. The champion cell achieved an efficiency of 17% and a VOC of 1.66 V, which was higher than the VOC's of the individual cells. The key challenge associated with Sn-containing perovskite is its instability due to the tendency for Sn2+ to oxidize into Sn4+.106 Over the years, this has been overcome by incorporating SnF2107 or metallic Sn powders17 in the perovskite precursor. Bulky organic cations, such as phenethylammonium (PEA)77 or guanidinium (Gua),74 have also been shown to be effective in reducing defects, thereby producing a high output voltage.

With regard to the fabrication method, physical deposition such as thermal evaporation has been explored to avoid the use of solution process which has the possibility of “dissolving” the bottom cell. Bolink and his colleagues67,70 have championed this work for “n-i-p” perovskite–perovskite tandem. Starting with an ITO coated substrate, compact TiO2 was deposited by solution processing as an electron transport layer (ETL) for the bottom cell. To reduce the recombination of the ETL/perovskite interface, fullerene derivative indene-C60-propionic acid hexyl ester (IPH) as an interlayer was deposited by solution processing. In their first work,67 the bottom high-bandgap Cs0.15FA0.85Pb(I0.3Br0.7)3 cell was fabricated by solution-processing while in their second work,67,70 the bottom cell CH3NH3PbI3 was fabricated by thermal evaporation, for the purpose of demonstrating all evaporated perovskite/perovskite tandem. Although the bandgap combination for the CH3NH3PbI3–CH3NH3PbI3 tandem was non-ideal for best current output, the output voltage was one of the highest achieved for perovskite–perovskite tandems. For thermally evaporated electron transport layer, fullerene C60 was used, which can by modulated by co-deposition of N1,N4-bis(tri-p-tolylphosphoranylidene) benzene-1,4-diamine (PhIm). For the hole transport material, N4,N4,N4″,N4″-tetra([1,1′-biphenyl]-4-yl)-[1,1′:4′,1″-terphenyl]-4,4″-diamine (TaTm) was evaporated and its conductivity can be tuned by doping it with 2,2′-(perfluoronaphthalene-2,6-diylidene) dimalononitrile (F6-TCNNQ) again via thermal evaporation. While physical-deposition is a promising approach for avoiding the use of solvent for the fabrication of perovskite–perovskite tandem, there remains scope for the demonstration of high-efficiency low-bandgap Sn–Pb perovskite cell by physical deposition.108,109

ITO or IZO was a popular choice for interfacing the top and bottom perovskite cells. For earlier demonstrations, their thickness were typically 100–130 nm, which was considered to be important for protecting the bottom cell from the solution processing of the top cell.66,68,69,73,74,76,78 It was later found that a 5 nm ITO or IZO was sufficient for this purpose by Palmstrom et al.75 They also reported that, for such thin transparent conductive layer to be effective, the depositions of a polyethylenimine (PEIE) layer by solution processing and an aluminum doped zinc oxide (AZO) layer by atomic layer deposition (ALD) were critical. The PEIE served as a nucleation layer for a dense and conformal AZO layer, which in turn allowed for a much thinner (5–10 nm) IZO to be deposited to form an efficient recombination junction.75 However, more recent perovskite–perovskite tandem demonstrations no longer needed ITO or IZO, which was replaced by an ALD SnOX layer (9–20 nm) accompanied by 1 nm Au clusters to form a recombination junction.17 This TCO-free design is suitable for large area tandems such as those demonstration by Yu et al.79 achieving 22.2% efficiency on 1.15 cm2 area and by Xiao et al.80 achieving a certified 24.2% efficiency on 1 cm2 area and an efficiency of 21.4% on 12 cm2 (first for perovskite–perovskite tandem >10 cm2). Most recently, the record efficiency of 26.4% on 0.049 cm2 has been reported by the same group.100 This is a milestone as the value exceeds the record efficiency of a single-junction perovskite solar cell.7 

A problem faced by the current perovskite–perovskite tandems is the lower output current when compared with perovskite–Si tandems [Fig. 3(b)]. This is due to the thinness of the narrow bandgap perovskite layer in many of the demonstrated tandems (<ideal 1100–1500 nm). Fabricating a thick narrow bandgap Sn-containing perovskite film is not trivial due to its lower wettability and lower solubility compared to Pb perovskites. In 2018, Leijtens et al.69 developed a route to fabricate uniform and thick (700 nm) FA0.75Cs0.25Sn0.5Pb0.5I3 by spin coating a high concentration (2.0 M) of perovskite precursor solution followed by anisole antisolvent immersion treatment and a methylammonium chloride (MACl) vapor accompanied by a short post-anneal at 150 °C. While the fabrication of thick films was essential for improving light absorption and current output, the vapor treatment and the short post-anneal promoted grain size growth and the healing of cracks boosting fill factor and output voltage of the associated devices. These techniques of using high-concentration precursor81 and Cl incorporation73 have been shown to be effective by other researchers in fabricating thick (700–900 nm) and high-quality tin-lead perovskites.

In 2019, Yang et al. reported that cadmium (Cd) incorporation (0.03%) reduces the trap density and improves the electron diffusion length of thick Sn–Pb perovskite.76 Another use of Cd may be the doping (≤5%) of the Pb–Sn perovskite which, according to density functional theory (DFT) simulation,110 can reduce its bandgap to 1.1 eV, closer to the ideal bandgap—0.96 eV for a bottom cell in a 2-junction tandem (Fig. 2). However, there is still a large disparity between the theoretical limit and the actual output voltage resulting in a voltage deficit (WOC = Eg/q – VOC) from Pb–Sn perovskites, larger than that of Pb-only perovskites. This is due to the low external radiative efficiency (ERE).14 This means there is no incentive to reduce the bandgap of the lower-bandgap-cell until the quality of the absorber layer is greatly improved. This means, in the short term, the bandgap of the bottom cell can be higher than ideal in order to deliver the required output voltage14 for tandems.

A 3-junction perovskite–perovskite–perovskite tandem will lower the burden placed on the bottom cell as mid- to low-energy incident photons will be distributed between the middle and bottom cells. As efficiencies of 2-junction tandems reach 30%, the rate of improvement may stagnate. Triple-junction concept provides an opportunity for an efficiency leap.116,117 While the theoretical efficiency for a triple-junction tandem is 51%,6 Horantner et al.118 reported that the practical efficiency limits for triple-junction perovskite–perovskite–perovskite cell would be 36.6% (with a bandgap combination of 2.04, 1.58, and 1.22 eV for the top, middle, and bottom cell, respectively) and for triple-junction perovskite–perovskite–Si cell would be 38.8% (for a combination of 1.95, 1.44, and 1.1 eV) as shown in Fig. 11.

FIG. 11.

Practical limits for triple junction. Simulated external quantum efficiencies and current–density voltage curves for ideal (a) and (c) perovskite–perovskite–perovskite and (b) and (d) perovskite–perovskite–Si tandems.118 Reproduced with permission from Hörantner et al., ACS Energy Lett. 2, 2506 (2017). Copyright 2017 American Chemical Society.

FIG. 11.

Practical limits for triple junction. Simulated external quantum efficiencies and current–density voltage curves for ideal (a) and (c) perovskite–perovskite–perovskite and (b) and (d) perovskite–perovskite–Si tandems.118 Reproduced with permission from Hörantner et al., ACS Energy Lett. 2, 2506 (2017). Copyright 2017 American Chemical Society.

Close modal

To date, there are three demonstrations of all perovskite triple-junction tandems112–114 and one on perovskite–perovskite–Si tandem.115 All these produced VOC ≥ 2.7 V. The best triple junction tandems113,114 produced FF × VOC products that are 73% of the practical limits reported in Ref. 118, suggesting a reasonable quality of interfacing between the cells in these perovskite–perovskite–perovskite tandems.113,114 There is a large scope for improvement in terms of current outputs which are well below the practical limits118 (only 55% for demonstrated perovskite–perovskite–Si tandems to 68% for demonstrated perovskite–perovskite–perovskite tandems). This is due to the large mismatch between the subcells as seen by their external quantum efficiencies (EQE).112–114 In these works, it is often the case that one subcell has an EQE of <60%, thereby limiting the output of the overall tandem, while subcells are connected in series sharing the same low current output. This shows the importance of good cell designs that minimize optical losses such as front reflection, Fresnel reflection, and parasitic absorptions in interlayers. However, the task is non-trivial as each additional subcell typically introduces three to four additional interlayers, contributing to optical losses and fabrication complexity.

To truly realize the full potentials of double- and triple-junction tandems that have theoretical power conversion efficiency of 45% and 51%, respectively, it is important that wide-bandgap cells deliver their potential output voltage, which multi-junction tandems rely on for achieving high efficiencies.119,120

Figure 12 shows that while some perovskite cells with bandgap (Eg) ≤ 1.8 eV have been able to produce VOC ∼ 90% of their theoretical limits29,34,36,42,49,52–54—relevant to double-junction tandems,56 cells with Eg > 1.8 eV (relevant to triple-junction tandems) have not been able to do so.121 This is due to the halide segregation that commonly occurs120 in the mixed Br–I perovskites with bandgaps <2.3 eV. Although high voltages can be achieved by tri-bromide perovskites (without the halide segregation), their bandgaps (∼2.3 eV) are too high for most multi-junction cells.6 Therefore, strategies for understanding121 and suppressing halide segregation (turning to inorganic cations122 to reduce the reliance on Br for tuning bandgap, for example) and strategies for maximizing voltage output from high-bandgap perovskite solar cells are critical for the success of perovskite tandem solar cells.

FIG. 12.

Reported photovoltaic parameters of perovskite solar cells of various bandgaps. The dashed lines indicate the proportions of the SQ limits.9,124–130,132–171

FIG. 12.

Reported photovoltaic parameters of perovskite solar cells of various bandgaps. The dashed lines indicate the proportions of the SQ limits.9,124–130,132–171

Close modal

Common strategies for maximizing voltages of small bandgap cells include compositional engineering,29,42 additive engineering,36,53,74,76 surface or bulk passivation51,73,80,123 can be translated to wide-bandgap cells [e.g., the use of Pb(SCN)2124 and formamidinium acetate123]. Two-dimensional (2D) perovskite layer for surface passivation employing n-butylammonium bromide,9,125 bilateral alkylamine additive, 1,3-diaminopropane,126 and iso-butylammonium127 have been reported to be effective. Doping or incorporation by Ba ions,128 Eu ions.129 Europium ion pair Eu3+-Eu2+130 and K ions131 have been reported to improve the quality of wide-bandgap perovskites. Apart from improving perovskite bulk quality and surface (including double sided passivations132) appropriate choice of carrier selective layers is also important.60,73 Not only can these provide additional passivation [e.g., in zwitterion-modified SnO2 electron transport layer (ETL)133] and achieve desirable work function (e.g., NH4Cl modification of ZnO ETL134 and self-assembled monolayer (SAM) with methyl group substitution Me-4PACz {[4–(3,6-dimethyl-9H-carbazol-9-yl)butyl] phosphonic acid} for hole transport layer (HTL)15,) to facilitate better carrier transport, but also they can influence the quality of the perovskite film subsequently deposited.134 Recently, LiF has become a popular interlayer as part of the ETL stack modification layer for high-efficiency high-bandgap perovskite cells31,44,51,52,85 in demonstrated tandems.

Regarding scale-up to large-area cell fabrication, learnings from the recently increasing effort in large-area single-junction cell demonstrations172 will be translated to tandems. However, the purpose or focus for flexible thin film tandems are different to those for perovskite–Si tandem. Perovskite–Si tandem deals with a flat, rigid substrate with a well-defined area. Perovskite–CIGS, perovskite–OPV, and perovskite–perovskite tandems on the other hand involve larger area deposition and require sectioning of the cells into strips followed by re-connection. The deposition methods also extend to roll-to-roll printing capitalizing on the flexible nature of thin film technologies. While there is a large scope of work, progress in large area perovskite-based thin film tandems will be at a slower pace compared to perovskite–Si tandems.

In terms of durability requirements, the expectation for perovskite–Si tandem will be higher as it is seen as a technology that will boost the performance of the incumbent. This is because, for tandems to be cost-effective, not only must the increase in cost in $/cell (due to the additional cost of fabricating the top perovskite cell) be matched by an increase in efficiency, but also the lifetime of the perovskite sub cell must match that of the Si solar cell.90 This may mean a 15-year-product warranty and 14% degradation performance warranty of 25 years allowing for 2% degradation in the 1st year followed by 0.5% degradation each successive year.1 For thin film perovskite tandems such as perovskite–CIGS, perovskite–OPV, and perovskite–perovskite tandems, while the expectations will be lower due to the lower technology readiness levels, the challenge will be no less due to the current reliance on Sn–Pb mixed perovskite for the bottom narrow bandgap cell, with Sn having a tendency to oxidize from Sn2+ to Sn4+ and the problem of halide segregation in high-bandgap mixed halide perovskites. Some of these issues may be overcome by the recently emerged two-dimensional (2D) metal halide perovskites,9,77,125,127,132,167 which have become a new favorite (evident by the increasing number of papers in recent years) because of the expanded range of material properties allowable improving their functionality and stability compared to 3D metal halide perovskites.

While some of the issues are unique to each technology, common challenges include the development of high-performance and stable wide-bandgap perovskite, which is most critical for the full potential of perovskite-multi-junction cells to be realized. It is believed that with the sustained research and development (R&D) followings of perovskite photovoltaics, continued progress will be made and breakthroughs in triple-junction tandems will be reported in the very near future.

A.W.Y.H.-B. and J.Z. contributed equally to this work.

This work was supported by the Australian Government through the Australian Renewable Energy Agency (ARENA) via Project Nos. 2020 RND001 and 2020 RND003 and the Australian Centre for Advanced Photovoltaics (ACAP) Postdoctoral Fellowships.

There are no conflicts to declare.

The data that support the findings of this study are available from the corresponding author upon reasonable request.

The data that support the findings in others' publications and are presented in this review are available from the corresponding authors of publications cited in this review. Restrictions may apply to the availability of these data.

1.
The Mechanical Engineering Industry Association for PV (VDMAPV)
,
International Technology Roadmap for Photovoltaic (ITRPV). 2019 Results
, 11th ed. (
Mechanical Engineering Industry Association for PV
,
2020
).
2.
P. K.
Nayak
,
S.
Mahesh
,
H. J.
Snaith
, and
D.
Cahen
, “
Photovoltaic solar cell technologies: Analysing the state of the art
,”
Nat. Rev. Mater.
4
(
4
),
269
285
(
2019
).
3.
R. M.
Swanson
, “
Approaching the 29% limit efficiency of silicon solar cells
,” in
Conference Record of the Thirty-First IEEE Photovoltaic Specialists Conference
(IEEE,
2005
), pp.
889
894
.
4.
A.
Richter
,
M.
Hermle
, and
S. W.
Glunz
, “
Reassessment of the limiting efficiency for crystalline silicon solar cells
,”
IEEE J. Photovoltaics
3
(
4
),
1184
1191
(
2013
).
5.
M. A.
Green
, “
Limiting photovoltaic efficiency under new ASTM International G173‐based reference spectra
,”
Prog. Photovoltaics
20
(
8
),
954
959
(
2012
).
6.
S. P.
Bremner
,
C.
Yi
,
I.
Almansouri
,
A.
Ho-Baillie
, and
M. A.
Green
, “
Optimum band gap combinations to make best use of new photovoltaic materials
,”
Sol. Energy
135
,
750
757
(
2016
).
7.
See https://www.nrel.gov/pv/cell-efficiency.html for
NREL
(last accessed Aug 19,
2021
).
8.
L. C.
Hirst
and
N.
Ekins‐Daukes
, “
Fundamental losses in solar cells
,”
Prog. Photovoltaics
19
(
3
),
286
293
(
2011
).
9.
T.
Duong
,
H.
Pham
,
T. C.
Kho
,
P.
Phang
,
K. C.
Fong
,
D.
Yan
,
Y.
Yin
,
J.
Peng
,
M. A.
Mahmud
,
S.
Gharibzadeh
,
B. A.
Nejand
,
I. M.
Hossain
,
M. R.
Khan
,
N.
Mozaffari
,
Y.
Wu
,
H.
Shen
,
J.
Zheng
,
H.
Mai
,
W.
Liang
,
C.
Samundsett
,
M.
Stocks
,
K.
McIntosh
,
G. G.
Andersson
,
U.
Lemmer
,
B. S.
Richards
,
U. W.
Paetzold
,
A.
Ho-Baillie
,
Y.
Liu
,
D.
Macdonald
,
A.
Blakers
,
J.
Wong‐Leung
,
T.
White
,
K.
Weber
, and
K.
Catchpole
, “
High efficiency perovskite–silicon tandem solar cells: Effect of surface coating versus bulk incorporation of 2D perovskite
,”
Adv. Energy Mater.
10
,
1903553
(
2020
).
10.
Y.
Ko
,
H.
Park
,
C.
Lee
,
Y.
Kang
, and
Y.
Jun
, “
Recent progress in interconnection layer for hybrid photovoltaic tandems
,”
Adv. Mater.
32
(
51
),
2002196
(
2020
).
11.
Z.
Zhu
,
K.
Mao
, and
J.
Xu
, “
Perovskite tandem solar cells with improved efficiency and stability
,”
J. Energy Chem.
58
,
219
232
(
2021
).
12.
M. A.
Green
,
A.
Ho-Baillie
, and
H. J.
Snaith
, “
The emergence of perovskite solar cells
,”
Nat. Photonics
8
(
7
),
506
514
(
2014
).
13.
A.
Kojima
,
K.
Teshima
,
Y.
Shirai
, and
T.
Miyasaka
, “
Organometal halide perovskites as visible-light sensitizers for photovoltaic cells
,”
J. Am. Chem. Soc.
131
(
17
),
6050
6051
(
2009
).
14.
M. A.
Green
and
A. W. Y.
Ho-Baillie
, “
Pushing to the limit: Radiative efficiencies of recent mainstream and emerging solar cells
,”
ACS Energy Lett.
4
(
7
),
1639
1644
(
2019
).
15.
A.
Al-Ashouri
,
E.
Köhnen
,
B.
Li
,
A.
Magomedov
,
H.
Hempel
,
P.
Caprioglio
,
J. A.
Márquez
,
A. B. M.
Vilches
,
E.
Kasparavicius
, and
J. A.
Smith
, “
Monolithic perovskite/silicon tandem solar cell with >29% efficiency by enhanced hole extraction
,”
Science
370
(
6522
),
1300
1309
(
2020
).
16.
Q.
Han
,
Y.-T.
Hsieh
,
L.
Meng
,
J.-L.
Wu
,
P.
Sun
,
E.-P.
Yao
,
S.-Y.
Chang
,
S.-H.
Bae
,
T.
Kato
,
V.
Bermudez
, and
Y.
Yang
, “
High-performance perovskite/Cu(In,Ga)Se2 monolithic tandem solar cells
,”
Science
361
(
6405
),
904
908
(
2018
).
17.
R.
Lin
,
K.
Xiao
,
Z.
Qin
,
Q.
Han
,
C.
Zhang
,
M.
Wei
,
M. I.
Saidaminov
,
Y.
Gao
,
J.
Xu
,
M.
Xiao
,
A.
Li
,
J.
Zhu
,
E. H.
Sargent
, and
H.
Tan
, “
Monolithic all-perovskite tandem solar cells with 24.8% efficiency exploiting comproportionation to suppress Sn(ii) oxidation in precursor ink
,”
Nat. Energy
4
(
10
),
864
873
(
2019
).
18.
X.
Chen
,
Z.
Jia
,
Z.
Chen
,
T.
Jiang
,
L.
Bai
,
F.
Tao
,
J.
Chen
,
X.
Chen
,
T.
Liu
,
X.
Xu
,
C.
Yang
,
W.
Shen
,
W. E. I.
Sha
,
H.
Zhu
, and
Y.
Yang
, “
Efficient and reproducible monolithic perovskite/organic tandem solar cells with low-loss interconnecting layers
,”
Joule
4
(
7
),
1594
1606
(
2020
).
19.
S.
Xie
,
R.
Xia
,
Z.
Chen
,
J.
Tian
,
L.
Yan
,
M.
Ren
,
Z.
Li
,
G.
Zhang
,
Q.
Xue
,
H.-L.
Yip
, and
Y.
Cao
, “
Efficient monolithic perovskite/organic tandem solar cells and their efficiency potential
,”
Nano Energy
78
,
105238
(
2020
).
20.
K.
Yoshikawa
,
H.
Kawasaki
,
W.
Yoshida
,
T.
Irie
,
K.
Konishi
,
K.
Nakano
,
T.
Uto
,
D.
Adachi
,
M.
Kanematsu
, and
H.
Uzu
, “
Silicon heterojunction solar cell with interdigitated back contacts for a photoconversion efficiency over 26%
,”
Nat. Energy
2
(
5
),
17032
(
2017
).
21.
M.
Nakamura
,
K.
Yamaguchi
,
Y.
Kimoto
,
Y.
Yasaki
,
T.
Kato
, and
H.
Sugimoto
, “
Cd-free Cu (In, Ga)(Se, S)2 thin-film solar cell with record efficiency of 23.35%
,”
IEEE J. Photovoltaics
9
(
6
),
1863
1867
(
2019
).
22.
J. P.
Mailoa
,
C. D.
Bailie
,
E. C.
Johlin
,
E. T.
Hoke
,
A. J.
Akey
,
W. H.
Nguyen
,
M. D.
McGehee
, and
T.
Buonassisi
, “
A 2-terminal perovskite/silicon multijunction solar cell enabled by a silicon tunnel junction
,”
Appl. Phys. Lett.
106
(
12
),
121105
(
2015
).
23.
S.
Albrecht
,
M.
Saliba
,
J. P.
Correa Baena
,
F.
Lang
,
L.
Kegelmann
,
M.
Mews
,
L.
Steier
,
A.
Abate
,
J.
Rappich
,
L.
Korte
,
R.
Schlatmann
,
M. K.
Nazeeruddin
,
A.
Hagfeldt
,
M.
Grätzel
, and
B.
Rech
, “
Monolithic perovskite/silicon-heterojunction tandem solar cells processed at low temperature
,”
Energy Environ. Sci.
9
(
1
),
81
88
(
2016
).
24.
J.
Werner
,
C. H.
Weng
,
A.
Walter
,
L.
Fesquet
,
J. P.
Seif
,
S.
De Wolf
,
B.
Niesen
, and
C.
Ballif
, “
Efficient monolithic perovskite/silicon tandem solar cell with cell area >1 cm2
,”
J. Phys. Chem. Lett.
7
(
1
),
161
166
(
2016
).
25.
J.
Werner
,
L.
Barraud
,
A.
Walter
,
M.
Bräuninger
,
F.
Sahli
,
D.
Sacchetto
,
N.
Tétreault
,
B.
Paviet-Salomon
,
S.-J.
Moon
,
C.
Allebé
,
M.
Despeisse
,
S.
Nicolay
,
S.
De Wolf
,
B.
Niesen
, and
C.
Ballif
, “
Efficient near-infrared-transparent perovskite solar cells enabling direct comparison of 4-terminal and monolithic perovskite/silicon tandem cells
,”
ACS Energy Lett.
1
,
474
480
(
2016
).
26.
J.
Werner
,
A.
Walter
,
E.
Rucavado
,
S.-J.
Moon
,
D.
Sacchetto
,
M.
Rienaecker
,
R.
Peibst
,
R.
Brendel
,
X.
Niquille
,
S.
De Wolf
,
P.
Löper
,
M.
Morales-Masis
,
S.
Nicolay
,
B.
Niesen
, and
C.
Ballif
, “
Zinc tin oxide as high-temperature stable recombination layer for mesoscopic perovskite/silicon monolithic tandem solar cells
,”
Appl. Phys. Lett.
109
(
23
),
233902
(
2016
).
27.
F.
Sahli
,
B. A.
Kamino
,
J.
Werner
,
M.
Bräuninger
,
B.
Paviet-Salomon
,
L.
Barraud
,
R.
Monnard
,
J. P.
Seif
,
A.
Tomasi
,
Q.
Jeangros
,
A.
Hessler-Wyser
,
S.
De Wolf
,
M.
Despeisse
,
S.
Nicolay
,
B.
Niesen
, and
C.
Ballif
, “
Improved optics in monolithic perovskite/silicon tandem solar cells with a nanocrystalline silicon recombination junction
,”
Adv. Energy Mater.
8
,
1701609
(
2017
).
28.
Y.
Wu
,
D.
Yan
,
J.
Peng
,
T.
Duong
,
Y.
Wan
,
P.
Phang
,
H.
Shen
,
N.
Wu
,
C.
Barugkin
,
X.
Fu
,
S.
Surve
,
D.
Walter
,
T.
White
,
K.
Catchpole
, and
K.
Weber
, “
Monolithic perovskite/silicon-homojunction tandem solar cell with over 22% efficiency
,”
Energy Environ. Sci.
10
(
11
),
2472
2479
(
2017
).
29.
R.
Fan
,
N.
Zhou
,
L.
Zhang
,
R.
Yang
,
Y.
Meng
,
L.
Li
,
T.
Guo
,
Y.
Chen
,
Z.
Xu
,
G.
Zheng
,
Y.
Huang
,
L.
Li
,
L.
Qin
,
X.
Qiu
,
Q.
Chen
, and
H.
Zhou
, “
Toward full solution processed perovskite/si monolithic tandem solar device with pce exceeding 20%
,”
Sol. RRL
1
(
11
),
1700149
(
2017
).
30.
J.
Zheng
,
C. F. J.
Lau
,
H.
Mehrvarz
,
F.-J.
Ma
,
Y.
Jiang
,
X.
Deng
,
A.
Soeriyadi
,
J.
Kim
,
M.
Zhang
,
L.
Hu
,
X.
Cui
,
D. S.
Lee
,
J.
Bing
,
Y.
Cho
,
C.
Chen
,
M. A.
Green
,
S.
Huang
, and
A. W. Y.
Ho-Baillie
, “
Large area efficient interface layer free monolithic perovskite/homo-junction-silicon tandem solar cell with over 20% efficiency
,”
Energy Environ. Sci.
11
(
9
),
2432
2443
(
2018
).
31.
F.
Sahli
,
J.
Werner
,
B. A.
Kamino
,
M.
Brauninger
,
R.
Monnard
,
B.
Paviet-Salomon
,
L.
Barraud
,
L.
Ding
,
J. J.
Diaz Leon
,
D.
Sacchetto
,
G.
Cattaneo
,
M.
Despeisse
,
M.
Boccard
,
S.
Nicolay
,
Q.
Jeangros
,
B.
Niesen
, and
C.
Ballif
, “
Fully textured monolithic perovskite/silicon tandem solar cells with 25.2% power conversion efficiency
,”
Nat. Mater.
17
(
9
),
820
826
(
2018
).
32.
K. A.
Bush
,
S.
Manzoor
,
K.
Frohna
,
Z. J.
Yu
,
J. A.
Raiford
,
A. F.
Palmstrom
,
H.-P.
Wang
,
R.
Prasanna
,
S. F.
Bent
,
Z. C.
Holman
, and
M. D.
McGehee
, “
Minimizing current and voltage losses to reach 25%-efficient monolithic two-terminal perovskite-silicon tandem solar cells
,”
ACS Energy Lett.
3
(
9
),
2713
2180
(
2018
).
33.
J.
Zheng
,
H.
Mehrvarz
,
F.-J.
Ma
,
C.-F. J.
Lau
,
M.
Green
,
S.
Huang
, and
A. W. Y.
Ho-Baillie
, “
21.8% efficient monolithic perovskite/homo-junction-silicon tandem solar cell on 16 cm2
,”
ACS Energy Lett.
3
(
9
),
2299
2300
(
2018
).
34.
S.
Zhu
,
F.
Hou
,
W.
Huang
,
X.
Yao
,
B.
Shi
,
Q.
Ren
,
J.
Chen
,
L.
Yan
,
S.
An
,
Z.
Zhou
,
H.
Ren
,
C.
Wei
,
Q.
Huang
,
Y.
Li
,
G.
Hou
,
X.
Chen
,
Y.
Ding
,
G.
Wang
,
B.
Li
,
Y.
Zhao
, and
X.
Zhang
, “
Solvent engineering to balance light absorbance and transmittance in perovskite for tandem solar cells
,”
Sol. RRL
2
(
11
),
1800176
(
2018
).
35.
Z.
Qiu
,
Z.
Xu
,
N.
Li
,
N.
Zhou
,
Y.
Chen
,
X.
Wan
,
J.
Liu
,
N.
Li
,
X.
Hao
,
P.
Bi
,
Q.
Chen
,
B.
Cao
, and
H.
Zhou
, “
Monolithic perovskite/Si tandem solar cells exceeding 22% efficiency via optimizing top cell absorber
,”
Nano Energy
53
,
798
807
(
2018
).
36.
B.
Chen
,
Z.
Yu
,
K.
Liu
,
X.
Zheng
,
Y.
Liu
,
J.
Shi
,
D.
Spronk
,
P. N.
Rudd
,
Z.
Holman
, and
J.
Huang
, “
Grain engineering for perovskite/silicon monolithic tandem solar cells with efficiency of 25.4%
,”
Joule
3
(
1
),
177
190
(
2018
).
37.
M.
Jošt
,
E.
Köhnen
,
A.
Morales Vilches
,
B.
Lipovšek
,
K.
Jäger
,
B.
Macco
,
A.
Al-Ashouri
,
J.
Krc
,
L.
Korte
,
B.
Rech
,
R.
Schlatmann
,
M.
Topic
,
B.
Stannowski
, and
S.
Albrecht
, “
Textured interfaces in monolithic perovskite/silicon tandem solar cells: Advanced light management for improved efficiency and energy yield
,”
Energy Environ. Sci.
11
(
12
),
3511
3523
(
2019
).
39.
M. A.
Green
,
E. D.
Dunlop
,
D. H.
Levi
,
J.
Hohl-Ebinger
,
M.
Yoshita
, and
A. W. Y.
Ho-Baillie
, “
Solar cell efficiency tables (version 54)
,”
IEEE J. Photovoltaics
27
(
7
),
565
575
(
2019
).
40.
F.
Hou
,
C.
Han
,
O.
Isabella
,
L.
Yan
,
B.
Shi
,
J.
Chen
,
S.
An
,
Z.
Zhou
,
W.
Huang
,
H.
Ren
,
Q.
Huang
,
G.
Hou
,
X.
Chen
,
Y.
Li
,
Y.
Ding
,
G.
Wang
,
C.
Wei
,
D.
Zhang
,
M.
Zeman
,
Y.
Zhao
, and
X.
Zhang
, “
Inverted pyramidally-textured PDMS antireflective foils for perovskite/silicon tandem solar cells with flat top cell
,”
Nano Energy
56
,
234
240
(
2019
).
41.
H.
Shen
,
S. T.
Omelchenko
,
D. A.
Jacobs
,
S.
Yalamanchili
,
Y.
Wan
,
D.
Yan
,
P.
Phang
,
T.
Duong
,
Y.
Wu
,
Y.
Yin
,
C.
Samundsett
,
J.
Peng
,
N.
Wu
,
T. P.
White
,
G. G.
Andersson
,
N. S.
Lewis
, and
K. R.
Catchpole
, “
In situ recombination junction between p-Si and TiO2 enables high-efficiency monolithic perovskite/Si tandem cells
,”
Sci. Adv.
4
(
12
),
eaau9711
(
2018
).
42.
F.
Hou
,
L.
Yan
,
B.
Shi
,
J.
Chen
,
S.
Zhu
,
Q.
Ren
,
S.
An
,
Z.
Zhou
,
H.
Ren
,
C.
Wei
,
Q.
Huang
,
G.
Hou
,
X.
Chen
,
Y.
Li
,
Y.
Ding
,
G.
Wang
,
D.
Zhang
,
Y.
Zhao
, and
X.
Zhang
, “
Monolithic perovskite/silicon-heterojunction tandem solar cells with open-circuit voltage of over 1.8 V
,”
ACS Appl. Energy Mater.
2
(
1
),
243
249
(
2019
).
43.
L.
Mazzarella
,
Y.-H.
Lin
,
S.
Kirner
,
A. B.
Morales-Vilches
,
L.
Korte
,
S.
Albrecht
,
E.
Crossland
,
B.
Stannowski
,
C.
Case
,
H. J.
Snaith
, and
R.
Schlatmann
, “
Infrared light management using a nanocrystalline silicon oxide interlayer in monolithic perovskite/silicon heterojunction tandem solar cells with efficiency above 25%
,”
Adv. Energy Mater.
9
,
1803241
(
2019
).
44.
G.
Nogay
,
F.
Sahli
,
J.
Werner
,
R.
Monnard
,
M.
Boccard
,
M.
Despeisse
,
F.-J.
Haug
,
Q.
Jeangros
,
A.
Ingenito
, and
C.
Ballif
, “
25.1%-efficient monolithic perovskite/silicon tandem solar cell based on a p-type mono-crystalline textured silicon wafer and high temperature passivating contacts
,”
ACS Energy Lett.
4
(
4
),
844
845
(
2019
).
45.
C. U.
Kim
,
J. C.
Yu
,
E. D.
Jung
,
I. Y.
Choi
,
W.
Park
,
H.
Lee
,
I.
Kim
,
D.-K.
Lee
,
K. K.
Hong
, and
M. H.
Song
, “
Optimization of device design for low cost and high efficiency planar monolithic perovskite/silicon tandem solar cells
,”
Nano Energy
60
,
213
221
(
2019
).
46.
B.
Kamino
,
B.
Paviet-Salomon
,
S.-J.
Moon
,
N.
Badel
,
J.
Levrat
,
G.
Christmann
,
A.
Walter
,
A.
Faes
,
L.
Ding
,
J. J.
Diaz Leon
,
A.
Paracchino
,
M.
Despeisse
,
C.
Ballif
, and
S.
Nicolay
, “
Low temperature screen-print metallization for the scale up of 2-terminal perovskite-silicon tandems
,”
ACS Appl. Energy Mater.
2
(
5
),
3815
3821
(
2019
).
47.
E.
Köhnen
,
M.
Jošt
,
A. B.
Morales-Vilches
,
P.
Tockhorn
,
A.
Al-Ashouri
,
B.
Macco
,
L.
Kegelmann
,
L.
Korte
,
B.
Rech
,
R.
Schlatmann
,
B.
Stannowski
, and
S.
Albrecht
, “
Highly efficient monolithic perovskite silicon tandem solar cells: Analyzing the influence of current mismatch on device performance
,”
Sustainable Energy Fuels
3
(
8
),
1995
2005
(
2019
).
48.
C. O.
Ramírez Quiroz
,
G. D.
Spyropoulos
,
M.
Salvador
,
L. M.
Roch
,
M.
Berlinghof
,
J.
Darío Perea
,
K.
Forberich
,
L. I.
Dion‐Bertrand
,
N. J.
Schrenker
,
A.
Classen
,
N.
Gasparini
,
G.
Chistiakova
,
M.
Mews
,
L.
Korte
,
B.
Rech
,
N.
Li
,
F.
Hauke
,
E.
Spiecker
,
T.
Ameri
,
S.
Albrecht
,
G.
Abellán
,
S.
León
,
T.
Unruh
,
A.
Hirsch
,
A.
Aspuru‐Guzik
, and
C. J.
Brabec
, “
Interface molecular engineering for laminated monolithic perovskite/silicon tandem solar cells with 80.4% fill factor
,”
Adv. Funct. Mater.
29
(
40
),
1901476
(
2019
).
49.
A. J.
Bett
,
P. S. C.
Schulze
,
K. M.
Winkler
,
Ö. S.
Kabakli
,
I.
Ketterer
,
L. E.
Mundt
,
S. K.
Reichmuth
,
G.
Siefer
,
L.
Cojocaru
,
L.
Tutsch
,
M.
Bivour
,
M.
Hermle
,
S. W.
Glunz
, and
J. C.
Goldschmidt
, “
Two‐terminal perovskite silicon tandem solar cells with a high‐bandgap perovskite absorber enabling voltages over 1.8 V
,”
Prog. Photovoltaics
28
(
2
),
99
110
(
2019
).
50.
B.
Chen
,
Z. J.
Yu
,
S.
Manzoor
,
S.
Wang
,
W.
Weigand
,
Z.
Yu
,
G.
Yang
,
Z.
Ni
,
X.
Dai
,
Z. C.
Holman
, and
J.
Huang
, “
Blade-coated perovskites on textured silicon for 26%-efficient monolithic perovskite/silicon tandem solar cells
,”
Joule
4
(
4
),
850
864
(
2020
).
51.
Y.
Hou
,
E.
Aydin
,
M.
De Bastiani
,
C.
Xiao
,
F. H.
Isikgor
,
D.-J.
Xue
,
B.
Chen
,
H.
Chen
,
B.
Bahrami
, and
A. H.
Chowdhury
, “
Efficient tandem solar cells with solution-processed perovskite on textured crystalline silicon
,”
Science
367
(
6482
),
1135
1140
(
2020
).
52.
J.
Xu
,
C. C.
Boyd
,
J. Y.
Zhengshan
,
A. F.
Palmstrom
,
D. J.
Witter
,
B. W.
Larson
,
R. M.
France
,
J.
Werner
,
S. P.
Harvey
, and
E. J.
Wolf
, “
Triple-halide wide–band gap perovskites with suppressed phase segregation for efficient tandems
,”
Science
367
(
6482
),
1097
1104
(
2020
).
53.
D.
Kim
,
H. J.
Jung
,
I. J.
Park
,
B. W.
Larson
,
S. P.
Dunfield
,
C.
Xiao
,
J.
Kim
,
J.
Tong
,
P.
Boonmongkolras
,
S. G.
Ji
,
F.
Zhang
,
S. R.
Pae
,
M.
Kim
,
S. B.
Kang
,
V.
Dravid
,
J. J.
Berry
,
J. Y.
Kim
,
K.
Zhu
,
D. H.
Kim
, and
B.
Shin
, “
Efficient, stable silicon tandem cells enabled by anion-engineered wide-bandgap perovskites
,”
Science
368
(
6487
),
155
160
(
2020
).
54.
P. S. C.
Schulze
,
A. J.
Bett
,
M.
Bivour
,
P.
Caprioglio
,
F. M.
Gerspacher
,
Ö. Ş.
Kabaklı
,
A.
Richter
,
M.
Stolterfoht
,
Q.
Zhang
,
D.
Neher
,
M.
Hermle
,
H.
Hillebrecht
,
S. W.
Glunz
, and
J. C.
Goldschmidt
, “
25.1% high‐efficient monolithic perovskite silicon tandem solar cell with a high band gap perovskite absorber
,”
Sol. RRL
4
(
7
),
2000152
(
2020
).
55.
A. S.
Subbiah
,
F. H.
Isikgor
,
C. T.
Howells
,
M.
De Bastiani
,
J.
Liu
,
E.
Aydin
,
F.
Furlan
,
T. G.
Allen
,
F.
Xu
,
S.
Zhumagali
,
S.
Hoogland
,
E. H.
Sargent
,
I.
McCulloch
, and
S. D.
Wolf
, “
High-performance perovskite single-junction and textured perovskite/silicon tandem solar cells via slot-die-coating
,”
ACS Energy Lett.
5
(
9
),
3034
3040
(
2020
).
56.
E.
Aydin
,
T. G.
Allen
,
M.
De Bastiani
,
L.
Xu
,
J.
Ávila
,
M.
Salvador
,
E.
Van Kerschaver
, and
S. D.
Wolf
, “
Interplay between temperature and bandgap energies on the outdoor performance of perovskite/silicon tandem solar cells
,”
Nat. Energy
5
(
11
),
851
859
(
2020
).
57.
M. D.
Bastiani
,
A. J.
Mirabelli
,
Y.
Hou
,
F.
Gota
,
E.
Aydin
,
T. G.
Allen
,
J.
Troughton
,
A. S.
Subbiah
,
F. H.
Isikgor
,
J.
Liu
,
L.
Xu
,
B.
Chen
,
E.
Van Kerschaver
,
D.
Baran
,
B.
Fraboni
,
M. F.
Salvador
,
U. W.
Paetzold
,
E. H.
Sargent
, and
S. D.
Wolf
, “
Efficient bifacial monolithic perovskite/silicon tandem solar cells via bandgap engineering
,”
Nat. Energy
6
,
167
175
(
2021
).
58.
T.
Todorov
,
T.
Gershon
,
O.
Gunawan
,
Y. S.
Lee
,
C.
Sturdevant
,
L. Y.
Chang
, and
S.
Guha
, “
Monolithic perovskite‐cigs tandem solar cells via in situ band gap engineering
,”
Adv. Energy Mater.
5
(
23
),
1500799
(
2015
).
59.
M.
Jost
,
T.
Bertram
,
D.
Koushik
,
J.
Marquez
,
M.
Verheijen
,
M. D.
Heinemann
,
E.
Köhnen
,
A.
Al-Ashouri
,
S.
Braunger
,
F.
Lang
,
B.
Rech
,
T.
Unold
,
M.
Creatore
,
I.
Lauermann
,
C. A.
Kaufmann
,
R.
Schlatmann
, and
S.
Albrecht
, “
21.6%-efficient monolithic perovskite/Cu(In,Ga)Se2 tandem solar cells with thin conformal hole transport layers for integration on rough bottom cell surfaces
,”
ACS Energy Lett.
4
(
2
),
583
590
(
2019
).
60.
A.
Al-Ashouri
,
A.
Magomedov
,
M.
Roß
,
M.
Jošt
,
M.
Talaikis
,
G.
Chistiakova
,
T.
Bertram
,
J. A.
Márquez
,
E.
Köhnen
,
E.
Kasparavičius
,
S.
Levcenco
,
L.
Gil-Escrig
,
C. J.
Hages
,
R.
Schlatmann
,
B.
Rech
,
T.
Malinauskas
,
T.
Unold
,
C. A.
Kaufmann
,
L.
Korte
,
G.
Niaura
,
V.
Getautis
, and
S.
Albrecht
, “
Conformal monolayer contacts with lossless interfaces for perovskite single junction and monolithic tandem solar cells
,”
Energy Environ. Sci.
12
(
11
),
3356
3369
(
2019
).
61.
F.
Fu
,
S.
Nishiwaki
,
J.
Werner
,
T.
Feurer
,
S.
Pisoni
,
Q.
Jeangros
,
S.
Buecheler
,
C.
Ballif
, and
A. N.
Tiwari
, “
Flexible perovskite/Cu (In, Ga) Se2 monolithic tandem solar cells
,” arXiv:1907.10330 (
2019
).
62.
T. J.
Jacobsson
,
A.
Hultqvist
,
S.
Svanström
,
L.
Riekehr
,
U. B.
Cappel
,
E.
Unger
,
H.
Rensmo
,
E. M. J.
Johansson
,
M.
Edoff
, and
G.
Boschloo
, “
2-Terminal CIGS-perovskite tandem cells: A layer by layer exploration
,”
Sol. Energy
207
,
270
288
(
2020
).
63.
M.
Jošt
,
A.
Al-Ashouri
,
B.
Lipovšek
,
T.
Bertram
,
R.
Schlatmann
,
C. A.
Kaufmann
,
M.
Topič
, and
S.
Albrecht
, “
Perovskite/CIGS tandem solar cells—Can they catch up with perovskite/c-Si tandems?
,” in
47th IEEE Photovoltaic Specialists Conference (PVSC)
(
2020
).
64.
F.
Jiang
,
T.
Liu
,
B.
Luo
,
J.
Tong
,
F.
Qin
,
S.
Xiong
,
Z.
Li
, and
Y.
Zhou
, “
A two-terminal perovskite/perovskite tandem solar cell
,”
J. Mater. Chem. A
4
(
4
),
1208
1213
(
2016
).
65.
J. H.
Heo
and
S. H.
Im
, “
CH3NH3PbBr3-CH3NH3PbI3 perovskite–perovskite tandem solar cells with exceeding 2.2 V open circuit voltage
,”
Adv. Mater.
28
(
25
),
5121
5125
(
2016
).
66.
G. E.
Eperon
,
T.
Leijtens
,
K. A.
Bush
,
R.
Prasanna
,
T.
Green
,
J. T.-W.
Wang
,
D. P.
McMeekin
,
G.
Volonakis
,
R. L.
Milot
, and
R.
May
, “
Perovskite–perovskite tandem photovoltaics with optimized band gaps
,”
Science
354
(
6314
),
861
865
(
2016
).
67.
D.
Forgács
,
L.
Gil‐Escrig
,
D.
Pérez‐Del‐Rey
,
C.
Momblona
,
J.
Werner
,
B.
Niesen
,
C.
Ballif
,
M.
Sessolo
, and
H. J.
Bolink
, “
Efficient monolithic perovskite/perovskite tandem solar cells
,”
Adv. Energy Mater.
7
(
8
),
1602121
(
2017
).
68.
A.
Rajagopal
,
Z.
Yang
,
S. B.
Jo
,
I. L.
Braly
,
P. W.
Liang
,
H. W.
Hillhouse
, and
A. K.
Jen
, “
Highly efficient perovskite–perovskite tandem solar cells reaching 80% of the theoretical limit in photovoltage
,”
Adv. Mater.
29
(
34
),
1702140
(
2017
).
69.
T.
Leijtens
,
R.
Prasanna
,
K. A.
Bush
,
G. E.
Eperon
,
J. A.
Raiford
,
A.
Gold-Parker
,
E. J.
Wolf
,
S. A.
Swifter
,
C. C.
Boyd
,
H.-P.
Wang
,
M. F.
Toney
,
S. F.
Bent
, and
M. D.
McGehee
, “
Tin–lead halide perovskites with improved thermal and air stability for efficient all-perovskite tandem solar cells
,”
Sustainable Energy Fuels
2
(
11
),
2450
2459
(
2018
).
70.
J.
Ávila
,
C.
Momblona
,
P.
Boix
,
M.
Sessolo
,
M.
Anaya
,
G.
Lozano
,
K.
Vandewal
,
H.
Míguez
, and
H. J.
Bolink
, “
High voltage vacuum-deposited CH3NH3PbI3–CH3NH3PbI3 tandem solar cells
,”
Energy Environ. Sci.
11
(
11
),
3292
3297
(
2018
).
71.
C.
Li
,
Z. S.
Wang
,
H. L.
Zhu
,
D.
Zhang
,
J.
Cheng
,
H.
Lin
,
D.
Ouyang
, and
W. C. H.
Choy
, “
Thermionic emission-based interconnecting layer featuring solvent resistance for monolithic tandem solar cells with solution-processed perovskites
,”
Adv. Energy Mater.
8
(
36
),
1801954
(
2018
).
72.
C.-Y.
Chang
,
B.-C.
Tsai
,
Y.-C.
Hsiao
,
M.-Z.
Lin
, and
H.-F.
Meng
, “
Solution-processed conductive interconnecting layer for highly-efficient and long-term stable monolithic perovskite tandem solar cells
,”
Nano Energy
55
,
354
367
(
2019
).
73.
D.
Zhao
,
C.
Chen
,
C.
Wang
,
M. M.
Junda
,
Z.
Song
,
C. R.
Grice
,
Y.
Yu
,
C.
Li
,
B.
Subedi
,
N. J.
Podraza
,
X.
Zhao
,
G.
Fang
,
R.-G.
Xiong
,
K.
Zhu
, and
Y.
Yan
, “
Efficient two-terminal all-perovskite tandem solar cells enabled by high-quality low-bandgap absorber layers
,”
Nat. Energy
3
,
1093
(
2018
).
74.
J.
Tong
,
Z.
Song
,
D. H.
Kim
,
X.
Chen
,
C.
Chen
,
A. F.
Palmstrom
,
P. F.
Ndione
,
M. O.
Reese
,
S. P.
Dunfield
, and
O. G.
Reid
, “
Carrier lifetimes of >1 μs in Sn–Pb perovskites enable efficient all-perovskite tandem solar cells
,”
Science
364
(
6439
),
475
479
(
2019
).
75.
A. F.
Palmstrom
,
G. E.
Eperon
,
T.
Leijtens
,
R.
Prasanna
,
S. N.
Habisreutinger
,
W.
Nemeth
,
E. A.
Gaulding
,
S. P.
Dunfield
,
M.
Reese
,
S.
Nanayakkara
,
T.
Moot
,
J.
Werner
,
J.
Liu
,
B.
To
,
S. T.
Christensen
,
M. D.
McGehee
,
M. F. A. M.
van Hest
,
J. M.
Luther
,
J. J.
Berry
, and
D. T.
Moore
, “
Enabling flexible all-perovskite tandem solar cells
,”
Joule
3
(
9
),
2193
2204
(
2019
).
76.
Z.
Yang
,
Z.
Yu
,
H.
Wei
,
X.
Xiao
,
Z.
Ni
,
B.
Chen
,
Y.
Deng
,
S. N.
Habisreutinger
,
X.
Chen
,
K.
Wang
,
J.
Zhao
,
P. N.
Rudd
,
J. J.
Berry
,
M. C.
Beard
, and
J.
Huang
, “
Enhancing electron diffusion length in narrow-bandgap perovskites for efficient monolithic perovskite tandem solar cells
,”
Nat. Commun.
10
(
1
),
4498
(
2019
).
77.
M.
Wei
,
K.
Xiao
,
G.
Walters
,
R.
Lin
,
Y.
Zhao
,
M. I.
Saidaminov
,
P.
Todorovic
,
A.
Johnston
,
Z.
Huang
,
H.
Chen
,
A.
Li
,
J.
Zhu
,
Z.
Yang
,
Y. K.
Wang
,
A. H.
Proppe
,
S. O.
Kelley
,
Y.
Hou
,
O.
Voznyy
,
H.
Tan
, and
E. H.
Sargent
, “
Combining efficiency and stability in mixed tin-lead perovskite solar cells by capping grains with an ultrathin 2D layer
,”
Adv. Mater
32
(
12
),
1907058
(
2020
).
78.
Z.
Song
,
D.
Zhao
,
C.
Chen
,
R. H.
Ahangharnejhad
,
C.
Li
,
K.
Ghimire
,
N. J.
Podraza
,
M. J.
Heben
,
K.
Zhu
, and
Y.
Yan
, paper
presented at the 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC)
(
2019
).
79.
Z.
Yu
,
Z.
Yang
,
Z.
Ni
,
Y.
Shao
,
B.
Chen
,
Y.
Lin
,
H.
Wei
,
J. Y.
Zhengshan
,
Z.
Holman
, and
J.
Huang
, “
Simplified interconnection structure based on C60/SnO2-x for all-perovskite tandem solar cells
,”
Nat. Energy
5
(
9
),
657
665
(
2020
).
80.
K.
Xiao
,
R.
Lin
,
Q.
Han
,
Y.
Hou
,
Z.
Qin
,
H. T.
Nguyen
,
J.
Wen
,
M.
Wei
,
V.
Yeddu
,
M. I.
Saidaminov
,
Y.
Gao
,
X.
Luo
,
Y.
Wang
,
H.
Gao
,
C.
Zhang
,
J.
Xu
,
J.
Zhu
,
E. H.
Sargent
, and
H.
Tan
, “
All-perovskite tandem solar cells with 24.2% certified efficiency and area over 1 cm2 using surface-anchoring zwitterionic antioxidant
,”
Nat. Energy
5
(
11
),
870
880
(
2020
).
81.
C.
Li
,
Z.
Song
,
C.
Chen
,
C.
Xiao
,
B.
Subedi
,
S. P.
Harvey
,
N.
Shrestha
,
K. K.
Subedi
,
L.
Chen
,
D.
Liu
,
Y.
Li
,
Y.-W.
Kim
,
C-s
Jiang
,
M. J.
Heben
,
D.
Zhao
,
R. J.
Ellingson
,
N. J.
Podraza
,
M.
Al-Jassim
, and
Y.
Yan
, “
Low-bandgap mixed tin–lead iodide perovskites with reduced methylammonium for simultaneous enhancement of solar cell efficiency and stability
,”
Nat. Energy
5
(
10
),
768
776
(
2020
).
82.
C.-C.
Chen
,
S.-H.
Bae
,
W.-H.
Chang
,
Z.
Hong
,
G.
Li
,
Q.
Chen
,
H.
Zhou
, and
Y.
Yang
, “
Perovskite/polymer monolithic hybrid tandem solar cells utilizing a low-temperature, full solution process
,”
Mater. Horiz.
2
(
2
),
203
211
(
2015
).
83.
Y.
Liu
,
L. A.
Renna
,
M.
Bag
,
Z. A.
Page
,
P.
Kim
,
J.
Choi
,
T.
Emrick
,
D.
Venkataraman
, and
T. P.
Russell
, “
High efficiency tandem thin-perovskite/polymer solar cells with a graded recombination layer
,”
ACS Appl. Mater. Interfaces
8
(
11
),
7070
7076
(
2016
).
84.
Z.
Li
,
S.
Wu
,
J.
Zhang
,
K. C.
Lee
,
H.
Lei
,
F.
Lin
,
Z.
Wang
,
Z.
Zhu
, and
A. K. Y.
Jen
, “
Hybrid perovskite‐organic flexible tandem solar cell enabling highly efficient electrocatalysis overall water splitting
,”
Adv. Energy Mater
10
(
18
),
2000361
(
2020
).
85.
K. A.
Bush
,
A. F.
Palmstrom
,
Z. J.
Yu
,
M.
Boccard
,
R.
Cheacharoen
,
J. P.
Mailoa
,
D. P.
McMeekin
,
R. L. Z.
Hoye
,
C. D.
Bailie
,
T.
Leijtens
,
I. M.
Peters
,
M. C.
Minichetti
,
N.
Rolston
,
R.
Prasanna
,
S.
Sofia
,
D.
Harwood
,
W.
Ma
,
F.
Moghadam
,
H. J.
Snaith
,
T.
Buonassisi
,
Z. C.
Holman
,
S. F.
Bent
, and
M. D.
McGehee
, “
23.6%-efficient monolithic perovskite/silicon tandem solar cells with improved stability
,”
Nat. Energy
2
(
4
),
17009
(
2017
).
86.
E.
Köhnen
,
P.
Wagner
,
F.
Lang
,
A.
Cruz
,
B.
Li
,
M.
Roß
,
M.
Jošt
,
A. B.
Morales-Vilches
,
M.
Topič
,
M.
Stolterfoht
,
D.
Neher
,
L.
Korte
,
B.
Rech
,
R.
Schlatmann
,
B.
Stannowski
, and
S.
Albrecht
, “
27.9% efficient monolithic perovskite/silicon tandem solar cells on industry compatible bottom cells
,”
Sol. RRL
5
,
2100244
(
2021
).
87.
F. H.
Isikgor
,
F.
Furlan
,
J.
Liu
,
E.
Ugur
,
M. K.
Eswaran
,
A. S.
Subbiah
,
E.
Yengel
,
M. D.
Bastiani
,
G. T.
Harrison
, and
S. J. J.
Zhumagali
, “
Concurrent cationic and anionic perovskite defect passivation enables 27.4% perovskite/silicon tandems with suppression of halide segregation
,”
Joule
5
(
6
),
1566
1586
(
2021
).
88.
C.
Case
, “
The path to perovskite performance and production (conference presentation)
,”
Proc. SPIE
10737
,
1073701
(
2018
).
89.
M.
Green
,
E.
Dunlop
,
J.
Hohl‐Ebinger
,
M.
Yoshita
,
N.
Kopidakis
, and
X.
Hao
, “
Solar cell efficiency tables (version 57)
,”
Prog. Photovoltaics
29
(
1
),
3
15
(
2020
).
90.
N. L.
Chang
,
J.
Zheng
,
Y.
Wu
,
H.
Shen
,
F.
Qi
,
K.
Catchpole
,
A.
Ho‐Baillie
, and
R. J.
Egan
, “
A bottom‐up cost analysis of silicon–perovskite tandem photovoltaics
,”
Prog. Photovoltaics
29
(
3
),
401
413
(
2021
).
91.
A.
Richter
,
R.
Müller
,
J.
Benick
,
F.
Feldmann
,
B.
Steinhauser
,
C.
Reichel
,
A.
Fell
,
M.
Bivour
,
M.
Hermle
, and
S. W.
Glunz
, “
Design rules for high-efficiency both-sides-contacted silicon solar cells with balanced charge carrier transport and recombination losses
,”
Nat. Energy
6
(
4
),
429
438
(
2021
).
92.
J.
Zheng
,
H.
Mehrvarz
,
C.
Liao
,
J.
Bing
,
X.
Cui
,
Y.
Li
,
V. R.
Gonçales
,
C.-F. J.
Lau
,
D. S.
Lee
,
Y.
Li
,
M.
Zhang
,
J.
Kim
,
Y.
Cho
,
L. G.
Caro
,
S.
Tang
,
C.
Chen
,
S.
Huang
, and
A. W. Y.
Ho-Baillie
, “
Large area 23%-efficient monolithic perovskite/homo-junction-silicon tandem solar cell with enhanced UV stability using down-shifting material
,”
ACS Energy Lett.
4
(
11
),
2623
2631
(
2019
).
93.
A.
Ho-Baillie
, “
Perovskites cover silicon textures
,”
Nat. Mater.
17
(
9
),
751
752
(
2018
).
94.
M. T.
Hörantner
and
H. J.
Snaith
, “
Predicting and optimising the energy yield of perovskite-on-silicon tandem solar cells under real world conditions
,”
Energy Environ. Sci.
10
(
9
),
1983
1993
(
2017
).
95.
Y. P.
Varshni
, “
Temperature dependence of the energy gap in semiconductors
,”
Physica
34
(
1
),
149
154
(
1967
).
96.
M. A.
Green
,
Y.
Jiang
,
A. M.
Soufiani
, and
A.
Ho-Baillie
, “
Optical properties of photovoltaic organic–inorganic lead halide perovskites
,”
J. Phys. Chem. Lett.
6
(
23
),
4774
4785
(
2015
).
97.
R. A.
Jishi
,
O. B.
Ta
, and
A. A.
Sharif
, “
Modeling of lead halide perovskites for photovoltaic applications
,”
J. Phys. Chem. C
118
(
49
),
28344
28349
(
2014
).
98.
J.
Kim
,
J. S.
Yun
,
Y.
Cho
,
D. S.
Lee
,
B.
Wilkinson
,
A. M.
Soufiani
,
X.
Deng
,
J.
Zheng
,
A.
Shi
,
S.
Lim
,
S.
Chen
,
Z.
Hameiri
,
M.
Zhang
,
C. F. J.
Lau
,
S.
Huang
,
M. A.
Green
, and
A. W. Y.
Ho-Baillie
, “
Overcoming the challenges of large-area high-efficiency perovskite solar cells
,”
ACS Energy Lett.
2
(
9
),
1978
1984
(
2017
).
99.
D.
Li
,
D.
Zhang
,
K. S.
Lim
,
Y.
Hu
,
Y.
Rong
,
A.
Mei
,
N. G.
Park
, and
H.
Han
, “
A review on scaling up perovskite solar cells
,”
Adv. Funct. Mater.
31
(
12
),
2008621
(
2020
).
100.
M. A.
Green
,
E. D.
Dunlop
,
J.
Hohl‐Ebinger
,
M.
Yoshita
,
N.
Kopidakis
, and
X.
Hao
, “
Solar cell efficiency tables (version 58)
,”
Prog. Photovoltaics
29
,
657
(
2021
).
101.
T. D.
Lee
and
A. U.
Ebong
, “
A review of thin film solar cell technologies and challenges
,”
Renewable Sustainable Energy Rev.
70
,
1286
1297
(
2017
).
102.
T.
Todorov
,
T.
Gershon
,
O.
Gunawan
,
C.
Sturdevant
, and
S.
Guha
, “
Perovskite-kesterite monolithic tandem solar cells with high open-circuit voltage
,”
Appl. Phys. Lett.
105
(
17
),
173902
(
2014
).
103.
M.
Jošt
,
A.
Al-Ashouri
,
B.
Lipovšek
,
T.
Bertram
,
R.
Schlatmann
,
C. A.
Kaufmann
,
M.
Topič
, and
S.
Albrecht
, paper
presented at the 2020 47th IEEE Photovoltaic Specialists Conference (PVSC)
(
2020
).
104.
X.
Xu
,
J.
Xiao
,
G.
Zhang
,
L.
Wei
,
X.
Jiao
,
H.-L.
Yip
, and
Y.
Cao
, “
Interface-enhanced organic solar cells with extrapolated T80 lifetimes of over 20 years
,”
Sci. Bull.
65
(
3
),
208
216
(
2020
).
105.
W.
Yang
,
Z.
Luo
,
R.
Sun
,
J.
Guo
,
T.
Wang
,
Y.
Wu
,
W.
Wang
,
J.
Guo
,
Q.
Wu
, and
M.
Shi
, “
Simultaneous enhanced efficiency and thermal stability in organic solar cells from a polymer acceptor additive
,”
Nat. Commun.
11
(
1
),
1218
(
2020
).
106.
C. C.
Stoumpos
,
C. D.
Malliakas
, and
M. G.
Kanatzidis
, “
Semiconducting tin and lead iodide perovskites with organic cations: Phase transitions, high mobilities, and near-infrared photoluminescent properties
,”
Inorg. Chem.
52
(
15
),
9019
9038
(
2013
).
107.
L.
Ma
,
F.
Hao
,
C. C.
Stoumpos
,
B. T.
Phelan
,
M. R.
Wasielewski
, and
M. G.
Kanatzidis
, “
Carrier diffusion lengths of over 500 nm in lead-free perovskite CH3NH3SnI3 films
,”
J. Am. Chem. Soc.
138
(
44
),
14750
14755
(
2016
).
108.
A. M.
Igual-Muñoz
,
J.
Ávila
,
P. P.
Boix
, and
H. J.
Bolink
, “
FAPb0.5Sn0.5I3: A narrow bandgap perovskite synthesized through evaporation methods for solar cell applications
,”
Solar RRL
4
(
2
),
1900283
(
2020
).
109.
J. M.
Ball
,
L.
Buizza
,
H. C.
Sansom
,
M. D.
Farrar
,
M. T.
Klug
,
J.
Borchert
,
J.
Patel
,
L. M.
Herz
,
M. B.
Johnston
, and
H. J. J. A. E. L.
Snaith
, “
Dual-source coevaporation of low-bandgap FA1–xCsxSn1–yPbyI3 perovskites for photovoltaics
,”
ACS Energy Lett.
4
(
11
),
2748
2756
(
2019
).
110.
H.
Choubisa
,
M.
Askerka
,
K.
Ryczko
,
O.
Voznyy
,
K.
Mills
,
I.
Tamblyn
, and
E. H. J. M.
Sargent
, “
Crystal site feature embedding enables exploration of large chemical spaces
,”
Matter
3
(
2
),
433
448
(
2020
).
111.
R.
Sheng
,
M. T.
Hoerantner
,
Z.
Wang
,
Y.
Jiang
,
W.
Zhang
,
A.
Agosti
,
S.
Huang
,
X.
Hao
,
A. W. Y.
Ho-Baillie
,
M. A.
Green
, and
H. J.
Snaith
, “
Monolithic wide band gap perovskite/perovskite tandem solar cells with organic recombination layers
,”
J. Phys. Chem. C
121
(
49
),
27256
27262
(
2017
).
112.
D. P.
McMeekin
,
S.
Mahesh
,
N. K.
Noel
,
M. T.
Klug
,
J.
Lim
,
J. H.
Warby
,
J. M.
Ball
,
L. M.
Herz
,
M. B.
Johnston
, and
H. J.
Snaith
, “
Solution-processed all-perovskite multi-junction solar cells
,”
Joule
3
(
2
),
387
401
(
2019
).
113.
K.
Xiao
,
J.
Wen
,
Q.
Han
,
R.
Lin
,
Y.
Gao
,
S.
Gu
,
Y.
Zang
,
Y.
Nie
,
J.
Zhu
,
J.
Xu
, and
H.
Tan
, “
Solution-processed monolithic all-perovskite triple-junction solar cells with efficiency exceeding 20%
,”
ACS Energy Lett.
5
(
9
),
2819
2826
(
2020
).
114.
J.
Wang
,
V.
Zardetto
,
K.
Datta
,
D.
Zhang
,
M. M.
Wienk
, and
R. A. J.
Janssen
, “
16.8% Monolithic all-perovskite triple-junction solar cells via a universal two-step solution process
,”
Nat. Commun.
11
(
1
),
5254
(
2020
).
115.
J.
Werner
,
F.
Sahli
,
F.
Fu
,
J. J.
Diaz Leon
,
A.
Walter
,
B. A.
Kamino
,
B.
Niesen
,
S.
Nicolay
,
Q.
Jeangros
, and
C.
Ballif
, “
Perovskite/perovskite/silicon monolithic triple-junction solar cells with a fully textured design
,”
ACS Energy Lett.
3
(
9
),
2052
2058
(
2018
).
116.
A. S.
Brown
and
M. A.
Green
, “
Detailed balance limit for the series constrained two terminal tandem solar cell
,”
Phys. E
14
(
1–2
),
96
100
(
2002
).
117.
A. D.
Vos
, “
Detailed balance limit of the efficiency of tandem solar cells
,”
J. Phys. D
13
(
5
),
839
(
1980
).
118.
M. T.
Hörantner
,
T.
Leijtens
,
M. E.
Ziffer
,
G. E.
Eperon
,
M. G.
Christoforo
,
M. D.
McGehee
, and
H. J.
Snaith
, “
The potential of multijunction perovskite solar cells
,”
ACS Energy Lett.
2
(
10
),
2506
2513
(
2017
).
119.
H.
Li
and
W.
Zhang
, “
Perovskite tandem solar cells: From fundamentals to commercial deployment
,”
Chem. Rev.
120
(
18
),
9835
9950
(
2020
).
120.
D. J.
Slotcavage
,
H. I.
Karunadasa
, and
M. D.
McGehee
, “
Light-induced phase segregation in halide-perovskite absorbers
,”
ACS Energy Lett.
1
(
6
),
1199
1205
(
2016
).
121.
W.
Mao
,
C. R.
Hall
,
S.
Bernardi
,
Y.-B.
Cheng
,
A.
Widmer-Cooper
,
T. A.
Smith
, and
U. J. N. m
Bach
, “
Light-induced reversal of ion segregation in mixed-halide perovskites
,”
Nat. Mater.
20
(
1
),
55
61
(
2021
).
122.
A.
Ho-Baillie
,
M.
Zhang
,
C. F. J.
Lau
,
F.-J.
Ma
, and
S.
Huang
, “
Untapped potentials of inorganic metal halide perovskite solar cells
,”
Joule
3
(
4
),
938
955
(
2019
).
123.
J.
Zhang
,
Z.
Wang
,
A.
Mishra
,
M.
Yu
,
M.
Shasti
,
W.
Tress
,
D. J.
Kubicki
,
C. E.
Avalos
,
H.
Lu
, and
Y.
Liu
, “
Intermediate phase enhances inorganic perovskite and metal oxide interface for efficient photovoltaics
,”
Joule
4
(
1
),
222
234
(
2020
).
124.
Y.
Zhou
,
Y. H.
Jia
,
H. H.
Fang
,
M. A.
Loi
,
F. Y.
Xie
,
L.
Gong
,
M. C.
Qin
,
X. H.
Lu
,
C. P.
Wong
, and
N.
Zhao
, “
Composition‐tuned wide bandgap perovskites: From grain engineering to stability and performance improvement
,”
Adv. Funct. Mater.
28
(
35
),
1803130
(
2018
).
125.
S.
Gharibzadeh
,
B.
Abdollahi Nejand
,
M.
Jakoby
,
T.
Abzieher
,
D.
Hauschild
,
S.
Moghadamzadeh
,
J. A.
Schwenzer
,
P.
Brenner
,
R.
Schmager
, and
A. A.
Haghighirad
, “
Record open‐circuit voltage wide‐bandgap perovskite solar cells utilizing 2D/3D perovskite heterostructure
,”
Adv. Energy Mater.
9
(
21
),
1803699
(
2019
).
126.
W.-Q.
Wu
,
Z.
Yang
,
P. N.
Rudd
,
Y.
Shao
,
X.
Dai
,
H.
Wei
,
J.
Zhao
,
Y.
Fang
,
Q.
Wang
, and
Y.
Liu
, “
Bilateral alkylamine for suppressing charge recombination and improving stability in blade-coated perovskite solar cells
,”
Sci. Adv.
5
(
3
),
eaav8925
(
2019
).
127.
M. A.
Mahmud
,
T.
Duong
,
Y.
Yin
,
J.
Peng
,
Y.
Wu
,
T.
Lu
,
H. T.
Pham
,
H.
Shen
,
D.
Walter
, and
H. T.
Nguyen
, “
In situ formation of mixed‐dimensional surface passivation layers in perovskite solar cells with dual‐isomer alkylammonium cations
,”
Small
16
(
49
),
2005022
(
2020
).
128.
W.
Xiang
,
Z.
Wang
,
D. J.
Kubicki
,
X.
Wang
,
W.
Tress
,
J.
Luo
,
J.
Zhang
,
A.
Hofstetter
,
L.
Zhang
, and
L.
Emsley
, “
Ba-induced phase segregation and band gap reduction in mixed-halide inorganic perovskite solar cells
,”
Nat. Commun.
10
(
1
),
4686
(
2019
).
129.
W.
Xiang
,
Z.
Wang
,
D. J.
Kubicki
,
W.
Tress
,
J.
Luo
,
D.
Prochowicz
,
S.
Akin
,
L.
Emsley
,
J.
Zhou
,
G.
Dietler
,
M.
Grätzel
, and
A.
Hagfeldt
, “
Europium-doped CsPbI2Br for stable and highly efficient inorganic perovskite solar cells
,”
Joule
3
(
1
),
205
214
(
2018
).
130.
L.
Wang
,
H.
Zhou
,
J.
Hu
,
B.
Huang
,
M.
Sun
,
B.
Dong
,
G.
Zheng
,
Y.
Huang
,
Y.
Chen
,
L.
Li
,
Z.
Xu
,
N.
Li
,
Z.
Liu
,
Q.
Chen
,
L.-D.
Sun
, and
C.-H.
Yan
, “
A Eu3+-Eu2+ ion redox shuttle imparts operational durability to Pb–I perovskite solar cells
,”
Science
363
(
6424
),
265
270
(
2019
).
131.
F.
Zheng
,
W.
Chen
,
T.
Bu
,
K. P.
Ghiggino
,
F.
Huang
,
Y.
Cheng
,
P.
Tapping
,
T. W.
Kee
,
B.
Jia
, and
X.
Wen
, “
Triggering the passivation effect of potassium doping in mixed‐cation mixed‐halide perovskite by light illumination
,”
Adv. Energy Mater.
9
(
24
),
1901016
(
2019
).
132.
M. A.
Mahmud
,
T.
Duong
,
Y.
Yin
,
H. T.
Pham
,
D.
Walter
,
J.
Peng
,
Y.
Wu
,
L.
Li
,
H.
Shen
, and
N.
Wu
, “
Double‐sided surface passivation of 3D perovskite film for high‐efficiency mixed‐dimensional perovskite solar cells
,”
Adv. Funct. Mater.
30
(
7
),
1907962
(
2020
).
133.
K.
Choi
,
J.
Lee
,
H. I.
Kim
,
C. W.
Park
,
G.-W.
Kim
,
H.
Choi
,
S.
Park
,
S. A.
Park
, and
T.
Park
, “
Thermally stable, planar hybrid perovskite solar cells with high efficiency
,”
Energy Environ. Sci.
11
(
11
),
3238
3247
(
2018
).
134.
H.
Wang
,
S.
Cao
,
B.
Yang
,
H.
Li
,
M.
Wang
,
X.
Hu
,
K.
Sun
, and
Z.
Zang
, “
NH4Cl-Modified ZnO for high-performance CsPbIBr2 perovskite solar cells via low-temperature process
,”
Sol. RRL
4
(
1
),
1900363
(
2020
).
135.
P.
Cui
,
D.
Wei
,
J.
Ji
,
H.
Huang
,
E.
Jia
,
S.
Dou
,
T.
Wang
,
W.
Wang
, and
M.
Li
, “
Planar p–n homojunction perovskite solar cells with efficiency exceeding 21.3%
,”
Nat. Energy
4
(
2
),
150
159
(
2019
).
136.
X.
Zhao
,
C.
Yao
,
T.
Liu
,
J. C.
Hamill
, Jr.
,,
G. O.
Ngongang Ndjawa
,
G.
Cheng
,
N.
Yao
,
H.
Meng
, and
Y. L.
Loo
, “
Extending the photovoltaic response of perovskite solar cells into the near‐infrared with a narrow‐bandgap organic semiconductor
,”
Adv. Mater.
31
(
49
),
1904494
(
2019
).
137.
N. J.
Jeon
,
J. H.
Noh
,
Y. C.
Kim
,
W. S.
Yang
,
S.
Ryu
, and
S. I.
Seok
, “
Solvent engineering for high-performance inorganic–organic hybrid perovskite solar cells
,”
Nat. Mater.
13
(
9
),
897
903
(
2014
).
138.
J. H.
Noh
,
S. H.
Im
,
J. H.
Heo
,
T. N.
Mandal
, and
S. I.
Seok
, “
Chemical management for colorful, efficient, and stable inorganic–organic hybrid nanostructured solar cells
,”
Nano Lett.
13
(
4
),
1764
1769
(
2013
).
139.
S. A.
Kulkarni
,
T.
Baikie
,
P. P.
Boix
,
N.
Yantara
,
N.
Mathews
, and
S.
Mhaisalkar
, “
Band-gap tuning of lead halide perovskites using a sequential deposition process
,”
J. Mater. Chem. A
2
(
24
),
9221
9225
(
2014
).
140.
H.
Tan
,
F.
Che
,
M.
Wei
,
Y.
Zhao
,
M. I.
Saidaminov
,
P.
Todorovic
,
D.
Broberg
,
G.
Walters
,
F.
Tan
,
T.
Zhuang
,
B.
Sun
,
Z.
Liang
,
H.
Yuan
,
E.
Fron
,
J.
Kim
,
Z.
Yang
,
O.
Voznyy
,
M.
Asta
, and
E. H.
Sargent
, “
Dipolar cations confer defect tolerance in wide-bandgap metal halide perovskites
,”
Nat. Commun.
9
(
1
),
3100
(
2018
).
141.
M. J.
Wu
,
C. C.
Kuo
,
L. S.
Jhuang
,
P. H.
Chen
,
Y. F.
Lai
, and
F. C.
Chen
, “
Bandgap engineering enhances the performance of mixed‐cation perovskite materials for indoor photovoltaic applications
,”
Adv. Energy Mater.
9
(
37
),
1901863
(
2019
).
142.
Y.
Lin
,
B.
Chen
,
F.
Zhao
,
X.
Zheng
,
Y.
Deng
,
Y.
Shao
,
Y.
Fang
,
Y.
Bai
,
C.
Wang
, and
J.
Huang
, “
Matching charge extraction contact for wide‐bandgap perovskite solar cells
,”
Adv. Mater.
29
(
26
),
1700607
(
2017
).
143.
Q.
Ye
,
Y.
Zhao
,
S.
Mu
,
F.
Ma
,
F.
Gao
,
Z.
Chu
,
Z.
Yin
,
P.
Gao
,
X.
Zhang
, and
J.
You
, “
Cesium lead inorganic solar cell with efficiency beyond 18% via reduced charge recombination
,”
Adv. Mater.
31
(
49
),
1905143
(
2019
).
144.
X.
Hu
,
X. F.
Jiang
,
X.
Xing
,
L.
Nian
,
X.
Liu
,
R.
Huang
,
K.
Wang
,
H. L.
Yip
, and
G.
Zhou
, “
Wide‐bandgap perovskite solar cells with large open‐circuit voltage of 1653 mV through interfacial engineering
,”
Sol. RRL
2
(
8
),
1800083
(
2018
).
145.
Y.-N.
Zhang
,
B.
Li
,
L.
Fu
,
Y.
Zou
,
Q.
Li
, and
L.-W.
Yin
, “
Enhanced optical absorption and efficient cascade electron extraction based on energy band alignment double absorbers perovskite solar cells
,”
Sol. Energy Mater. Sol. Cells
194
,
168
176
(
2019
).
146.
M.
Chen
,
M.-G.
Ju
,
A. D.
Carl
,
Y.
Zong
,
R. L.
Grimm
,
J.
Gu
,
X. C.
Zeng
,
Y.
Zhou
, and
N. P.
Padture
, “
Cesium titanium (IV) bromide thin films based stable lead-free perovskite solar cells
,”
Joule
2
(
3
),
558
570
(
2018
).
147.
S.
Yang
,
H.
Zhao
,
Y.
Han
,
C.
Duan
,
Z.
Liu
, and
S.
Liu
, “
Europium and acetate Co‐doping strategy for developing stable and efficient CsPbI2Br perovskite solar cells
,”
Small
15
(
46
),
1904387
(
2019
).
148.
H.
Zhao
,
Y.
Han
,
Z.
Xu
,
C.
Duan
,
S.
Yang
,
S.
Yuan
,
Z.
Yang
,
Z.
Liu
, and
S.
Liu
, “
A novel anion doping for stable CsPbI2Br perovskite solar cells with an efficiency of 15.56% and an open circuit voltage of 1.30 V
,”
Adv. Energy Mater.
9
(
40
),
1902279
(
2019
).
149.
C.
Duan
,
J.
Cui
,
M.
Zhang
,
Y.
Han
,
S.
Yang
,
H.
Zhao
,
H.
Bian
,
J.
Yao
,
K.
Zhao
, and
Z.
Liu
, “
Precursor engineering for ambient‐compatible antisolvent‐free fabrication of high‐efficiency CsPbI2Br perovskite solar cells
,”
Adv. Energy Mater.
10
(
22
),
2000691
(
2020
).
150.
H.
Bian
,
D.
Bai
,
Z.
Jin
,
K.
Wang
,
L.
Liang
,
H.
Wang
,
J.
Zhang
,
Q.
Wang
, and
S. F.
Liu
, “
Graded bandgap CsPbI2+xBr1−x perovskite solar cells with a stabilized efficiency of 14.4%
,”
Joule
2
(
8
),
1500
1510
(
2018
).
151.
Y.
Zhao
,
A. M.
Nardes
, and
K.
Zhu
, “
Mesoporous perovskite solar cells: Material composition, charge-carrier dynamics, and device characteristics
,”
Faraday Discuss.
176
,
301
312
(
2014
).
152.
R.
Nie
,
A.
Mehta
,
B. W.
Park
,
H. W.
Kwon
,
J.
Im
, and
S. I.
Seok
, “
Mixed sulfur and iodide-based lead-free perovskite solar cells
,”
J. Am. Chem. Soc.
140
(
3
),
872
875
(
2018
).
153.
Q.
Xue
,
G.
Chen
,
M.
Liu
,
J.
Xiao
,
Z.
Chen
,
Z.
Hu
,
X. F.
Jiang
,
B.
Zhang
,
F.
Huang
, and
W.
Yang
, “
Improving film formation and photovoltage of highly efficient inverted‐type perovskite solar cells through the incorporation of new polymeric hole selective layers
,”
Adv. Energy Mater.
6
(
5
),
1502021
(
2016
).
154.
W.
Zhu
,
Z.
Zhang
,
W.
Chai
,
Q.
Zhang
,
D.
Chen
,
Z.
Lin
,
J.
Chang
,
J.
Zhang
,
C.
Zhang
, and
Y.
Hao
, “
Band alignment engineering towards high efficiency carbon‐based inorganic planar CsPbIBr2 perovskite solar cells
,”
ChemSusChem
12
(
10
),
2318
2325
(
2019
).
155.
T.
Bu
,
X.
Liu
,
R.
Chen
,
Z.
Liu
,
K.
Li
,
W.
Li
,
Y.
Peng
,
Z.
Ku
,
F.
Huang
, and
Y.-B.
Cheng
, “
Organic/inorganic self-doping controlled crystallization and electronic properties of mixed perovskite solar cells
,”
J. Mater. Chem. A
6
(
15
),
6319
6326
(
2018
).
156.
F.
Jiang
,
D.
Yang
,
Y.
Jiang
,
T.
Liu
,
X.
Zhao
,
Y.
Ming
,
B.
Luo
,
F.
Qin
,
J.
Fan
, and
H.
Han
, “
Chlorine-incorporation-induced formation of the layered phase for antimony-based lead-free perovskite solar cells
,”
J. Am. Chem. Soc.
140
(
3
),
1019
1027
(
2018
).
157.
B. W.
Park
,
B.
Philippe
,
X.
Zhang
,
H.
Rensmo
,
G.
Boschloo
, and
E. M.
Johansson
, “
Bismuth based hybrid perovskites A3Bi2I9 (A: Methylammonium or cesium) for solar cell application
,”
Adv. Mater.
27
(
43
),
6806
6813
(
2015
).
158.
F.
Umar
,
J.
Zhang
,
Z.
Jin
,
I.
Muhammad
,
X.
Yang
,
H.
Deng
,
K.
Jahangeer
,
Q.
Hu
,
H.
Song
, and
J.
Tang
, “
Dimensionality controlling of Cs3Sb2I9 for efficient all‐inorganic planar thin film solar cells by HCl‐assisted solution method
,”
Adv. Opt. Mater.
7
(
5
),
1801368
(
2019
).
159.
Y.
Zhang
,
Y.
Liang
,
Y.
Wang
,
F.
Guo
,
L.
Sun
, and
D.
Xu
, “
Planar FAPbBr3 solar cells with power conversion efficiency above 10%
,”
ACS Energy Lett.
3
(
8
),
1808
1814
(
2018
).
160.
J.
Duan
,
Y.
Zhao
,
B.
He
, and
Q.
Tang
, “
High‐purity inorganic perovskite films for solar cells with 9.72% efficiency
,”
Angew. Chem. Int. Ed.
130
(
14
),
3849
3853
(
2018
).
161.
G.
Liao
,
J.
Duan
,
Y.
Zhao
, and
Q.
Tang
, “
Toward fast charge extraction in all-inorganic CsPbBr3 perovskite solar cells by setting intermediate energy levels
,”
Sol. Energy
171
,
279
285
(
2018
).
162.
X.
Wan
,
Z.
Yu
,
W.
Tian
,
F.
Huang
,
S.
Jin
,
X.
Yang
,
Y.-B.
Cheng
,
A.
Hagfeldt
, and
L.
Sun
, “
Efficient and stable planar all-inorganic perovskite solar cells based on high-quality CsPbBr3 films with controllable morphology
,”
J. Energy Chem.
46
,
8
15
(
2020
).
163.
J.
Zhu
,
M.
Tang
,
B.
He
,
W.
Zhang
,
X.
Li
,
Z.
Gong
,
H.
Chen
,
Y.
Duan
, and
Q.
Tang
, “
Improved charge extraction through interface engineering for 10.12% efficiency and stable CsPbBr3 perovskite solar cells
,”
J. Mater. Chem. A
8
(
40
),
20987
20997
(
2020
).
164.
Y.
Zhao
,
J.
Duan
,
Y.
Wang
,
X.
Yang
, and
Q.
Tang
, “
Precise stress control of inorganic perovskite films for carbon-based solar cells with an ultrahigh voltage of 1.622 V
,”
Nano Energy
67
,
104286
(
2020
).
165.
Y.
Zhao
,
J.
Duan
,
H.
Yuan
,
Y.
Wang
,
X.
Yang
,
B.
He
, and
Q.
Tang
, “
Using SnO2 QDs and CsMBr3 (M = Sn, Bi, Cu) QDs as charge‐transporting materials for 10.6%‐efficiency all‐inorganic CsPbBr3 perovskite solar cells with an ultrahigh open‐circuit voltage of 1.610 V
,”
Sol. RRL
3
(
3
),
1800284
(
2019
).
166.
C. H.
Ng
,
T. S.
Ripolles
,
K.
Hamada
,
S. H.
Teo
,
H. N.
Lim
,
J.
Bisquert
, and
S.
Hayase
, “
Tunable open circuit voltage by engineering inorganic cesium lead bromide/iodide perovskite solar cells
,”
Sci. Rep.
8
(
1
),
2482
(
2018
).
167.
M.
Safdari
,
P. H.
Svensson
,
M. T.
Hoang
,
I.
Oh
,
L.
Kloo
, and
J. M.
Gardner
, “
Layered 2D alkyldiammonium lead iodide perovskites: Synthesis, characterization, and use in solar cells
,”
J. Mater. Chem. A
4
(
40
),
15638
15646
(
2016
).
168.
Y.
Zhao
,
H.
Xu
,
Y.
Wang
,
X.
Yang
,
J.
Duan
, and
Q.
Tang
, “
10.34%-efficient integrated CsPbBr3/bulk-heterojunction solar cells
,”
J. Power Sources
440
,
227151
(
2019
).
169.
G.
Murugadoss
,
R.
Thangamuthu
,
S. M. S.
Kumar
,
N.
Anandhan
,
M. R.
Kumar
, and
A.
Rathishkumar
, “
Synthesis of ligand-free, large scale with high quality all-inorganic CsPbI3 and CsPb2Br5 nanocrystals and fabrication of all-inorganic perovskite solar cells
,”
J. Alloys Compd.
787
,
17
26
(
2019
).
170.
L.
Zuo
,
X.
Shi
,
W.
Fu
, and
A. K. Y.
Jen
, “
Highly efficient semitransparent solar cells with selective absorption and tandem architecture
,”
Adv. Mater.
31
(
36
),
1901683
(
2019
).
171.
E.
Greul
,
M. L.
Petrus
,
A.
Binek
,
P.
Docampo
, and
T.
Bein
, “
Highly stable, phase pure Cs2AgBiBr6 double perovskite thin films for optoelectronic applications
,”
J. Mater. Chem. A
5
(
37
),
19972
19981
(
2017
).
172.
T.
Bu
,
J.
Li
,
H.
Li
,
C.
Tian
,
J.
Su
,
G.
Tong
,
L. K.
Ono
,
C.
Wang
,
Z.
Lin
, and
N. J. S.
Chai
, “
Lead halide–templated crystallization of methylamine-free perovskite for efficient photovoltaic modules
,”
Science
372
(
6548
),
1327
1332
(
2021
).