Design and numerical analysis of CIGS-based solar cell with V₂O₅ as the BSF layer to enhance photovoltaic performance

The evolution of renewable and green energy sources to counterbalance the negative impacts of CO₂ emissions caused by the use of fossil resources has been a key goal for scientists and researchers worldwide.^1–4 Photovoltaic (PV) cells are good renewable sources of energy that are critical to addressing the expanding energy requirements and assuring green power, with the net PV power growing at a pace of roughly 8.3% each year.^5,6 Because it is renewable, plentiful, and eco-friendly, solar energy has emerged as the dominant substitute for fossil fuels.^7–10 As solar energy is collected from the sun, it is the most dependable green energy source. PV solar cells create energy from the radiation of the sun by utilizing photoconductivity and are classified into two categories: thin and bulk. Thin-film solar cells (TFSCs) are more popular because they have a lower cost. Dye-sensitized solar cells (DSSCs) are a subset of TFSCs that have been the subject of in-depth study for more than 20 years. However, they have certain stability problems.^11–13 The most widely used and efficient TFSCs are CdTe and chalcopyrite Cu(In, Ga)Se₂ (CIGS)-based solar cells.¹⁴ TFSCs are gaining popularity because of their high efficiency, low price, and enhanced stability. Because of the high cost and power requirement for manufacturing Si in bulk, first-generation thick crystalline Si-based solar cells are less feasible to use,^15–20 and as a result, extensive research on second-generation TFSCs employing semiconductor materials such as CIGS, copper zinc tin sulfide (CZTS), and others has begun.^21–24 

Amorphous silicon (a-Si), quantum dots, polycrystalline CdTe thin-film, and CIGS solar cells make up 13% of the market,²⁵ and lower production costs, higher efficiency, and remarkable stability in a wide range of circumstances are necessary to improve this market share.²⁶ The efficiency of Si-based solar cells can reach about 24.5%, while CdTe-based solar cells can have up to 21% efficiency.²⁷ The theoretical peak efficiency of 30% for a single p-n junction solar cell has been estimated by the Shockley–Queisser limit. The efficiency of CIGS-based solar cells approaches and seeks to cross the Shockley–Queisser limit. CIGS TFSCs have achieved high efficiency and are a viable option for commercially feasible applications on a broad scale. Because of their reliability at high temperatures along with low volume and weight, CIGS-based solar cells can play an important role in aerospace applications.²⁸ 

To produce highly efficient CIGS PV solar cells, the co-evaporation process is typically used.²⁹ The bandgap (E_g) is around 1.04 eV for the copper indium selenium (CuInSe₂) or CIS absorber layer,²⁹ and for the CIGS absorber, the bandgap ranges from 1 to 1.7 eV after incorporating gallium into the CIS absorber.³⁰ Even so, the CIGS absorber layer’s optimal bandgap is around 1.16 eV.³¹ The buffer layer, which is positioned between the layers of the absorber and window, imparts structural stability and controls the internal electrostatic fields of the absorber.³² The buffer layer is commonly used as a focal point in the heterojunction TFSCs. From the front surface layer, photons go through the buffer layer before reaching the absorber layer. Hence, in the buffer layer, the absorption of photons should be minimum, and some properties, such as surface recombination and electrical resistance, are required in the buffer layer. Hence, the buffer layer’s bandgap should be quite large so that the absorber layer may absorb the greatest quantity of photons. On the contrary, the bandgap margins of both absorber and buffer layers must be substantially well-suited. Metal chalcogenides, such as CdS, CdSe, ZnSe, and In₂S₃, exhibit excellent characteristics as buffer layers in heterojunction TFSCs. However, the most commonly used buffer layers, CdS and CdSe, are harmful to the environment.³³ Greener, less harmful components, such as ZnS, ZnSe, ZnO, Zn_1−xMg_xO, and In₂S₃, can be considered as replacements for these toxic buffer layers.³⁴ The impact of different buffer layers on the solar cells can be investigated using numerical simulation to improve the device’s performance.^35–37 Due to its environmental friendliness, ZnSe can be a good replacement for the harmful CdS buffer layer. Because ZnSe has a larger bandgap than CdS, its usual absorption range is around 450 nm, whereas for CdS, it is around 500 nm. As a result, using ZnSe as a buffer layer may help avoid the loss of photons in the visible light range that can produce charge carriers and contribute to photocurrent.³⁸ Furthermore, using ZnSe as a buffer layer in CIGS-based solar cells can improve the performance of the solar cell by reducing recombination losses at the CIGS/buffer interface. The recombination losses occur when the electrons and holes generated in the CIGS absorber recombine at the buffer layer interface, resulting in a loss of power. ZnSe is a promising buffer material for CIGS-based solar cells because it has a bandgap that is higher than that of CIGS and has high electron mobility. This allows for efficient charge transport and reduced recombination losses at the interface. In addition, ZnSe has high thermal stability and chemical resistance, making it suitable for usage during high-temperature processing. Deposition factors, circumstances, and procedures, as well as pre- and post-treatments, have significant effects on the physical characteristics of ZnSe solar films.³⁹ For producing high-quality films and optoelectronic devices, one of the vital steps is thermal annealing.⁴⁰ To develop ZnSe thin films, a variety of growth processes are now available, including electron beam evaporation,⁴¹ sputtering,⁴² chemical bath deposition,⁴³ thermal evaporation,⁴⁴ etc.

Moreover, a back surface field (BSF) is a highly doped area on the solar cell’s back surface. Different inorganic transition metal oxides (TMOs), such as WO₃, CuI, V₂O₅, and NiO, have been included in the heterojunction solar cells as the BSF layer for increasing their performance and stability.^45,46 Among these TMOs, V₂O₅ has multiple distinguishing characteristics, including great ambient stability and good electrical and optical properties. The V₂O₅ film can be fabricated by a very low-cost and simple spin-coating fabrication technique.⁴⁷ The significance of using a novel ZnSe/CIGS/V₂O₅ combination is that the ZnSe buffer layer reduces recombination losses at the CIGS/ZnSe interface while the V₂O₅ BSF layer improves the collection of the generated charge carriers. The combination of ZnSe and V₂O₅ with a CIGS absorber allows for improved charge transport, reduced recombination losses, and improved collection of charge carriers. Hence, ZnSe/CIGS/V₂O₅ heterostructure provides efficient transportation of electrons and holes in photoactive layers, resulting in improved efficiency; this allows the simulated solar cell to perform well under various conditions.⁴⁷ 

In this work, we have investigated a fully inorganic PV device with a heterostructure of SnO₂:F (FTO)/ZnSe/CIGS/V₂O₅/Cu. We have studied the impact of absorber thickness, bulk defect density, acceptor density, buffer layer thickness, interfacial defect density, working temperatures, and series and shunt resistances on the device performance. Furthermore, a comparative study between this work and previous reports has also been carried out. The proposed heterostructure in this simulation study can act as a guide for the experimental fabrication of low-cost and non-toxic CIGS-based thin-film devices utilizing several promising fabrication routes, including spin-coating, co-evaporation,²⁹ sputtering,⁴⁸ physical vapor deposition,⁴⁹ or electro-deposition.⁵⁰ 

During the modeling of the solar cell, simulation parameters have been taken based on theoretical analysis, literature research, and other factors. Figure 1 depicts the proposed FTO/ZnSe/CIGS/V₂O₅/Cu model that includes CIGS as the absorber layer, which is a p-type semiconductor having a bandgap of 1.15 eV.⁵¹ ZnSe is utilized as the n-type buffer layer with a bandgap of 2.9 eV,^33,52 while V₂O₅, with a bandgap of 2.2 eV, acts as the BSF layer to enhance the device’s performance.⁴⁶ Besides, FTO is used as the window layer having a bandgap of 3.6 eV. In the back grid contact, copper (Cu) is employed with a metal surface work function (WF) of 5.1 eV.

The bandgap of each material, electron affinity, dielectric permittivity, electron mobility, hole mobility, and almost all the characteristics of the materials are graded in SCAPS-1D. In Table I, the parameter values utilized in this model are listed.

The initial temperature is taken as 300 K with standard illumination of AM1.5G, and all the simulations are run at 1000 W m⁻² solar power. In addition, initially, the solar cell’s series and shunt resistances are assumed to be zero and infinitely high, respectively, the same as in an ideal PV cell. Furthermore, the band alignment determines how much current will pass through the heterojunction. The recommended solar cell’s energy band diagram is depicted in Fig. 2, which is achieved from the band energy panel of the SCAPS-1D software.

SCAPS-1D software has been used to reveal the impact of various absorber layer thicknesses. The numerical findings also show how the addition of the V₂O₅ BSF layer affects the device’s performance.

The absorber thickness has a noticeable influence on the PV performance of the device as it affects the diffusion lengths of the charge carriers. When the absorber is too thick, the charge carriers might recombine before reaching the charge-collecting electrodes; conversely, an ultrathin absorber layer is unable to absorb a significant part of the incident radiation, thereby reducing the overall device performance. Figure 3(a) depicts the effect of CIGS absorber thickness on the performance of the FTO/ZnSe/CIGS/Cu model without BSF. As the thickness of the CIGS absorber has been changed from 0.1 to 3 µm, the open-circuit voltage (V_OC), short-circuit current density (J_SC), fill factor (FF), and photoconversion efficiency (PCE or η) follow an upward trend. As a larger number of photons coming from solar irradiation get absorbed when the absorber thickness is increased, J_SC and PCE increase. Hence, the PCEs of the absorber with a thickness of 0.1 and 3 µm are 5.3% and 23.81%, respectively. For an absorber of 3 µm thickness, the V_OC, J_SC, and FF are 0.73 V, 40.09 mA/cm², and 80.84%, respectively, which are comparable to the 85% FF,^26,60 0.64–0.69 V V_OC,^28,57,58,61 and 40 mA/cm² J_SC⁶² values reported in the previous studies. It is also noticed that when the absorber thickness is 3 µm, the V_OC, J_SC, FF, and PCE are the highest. However, the cost for the absorber layer also increases at the same time due to the higher thickness.

For BSF, a p⁺-type semiconductor is used. Surface recombination is one of the reasons for getting less performance due to the recombination of the electrons (minority charge carrier) at the back contact region. Hence, the recombination should be limited. To prevent higher recombination, a BSF layer can be added to the backside of the PV cell, which has a higher doping concentration than the p-type absorber.⁶³ Throughout this work, a thin V₂O₅ layer, with a thickness of 0.05 µm and doping concentration of 1 × 10¹⁹ cm⁻³, has been inserted next to the CIGS absorber to work as a BSF layer. The V₂O₅ BSF (p⁺-type) and CIGS absorber (p-type) interface work as a p-n junction. This BSF layer can serve as a barrier to the minority carrier from going to the back surface by creating an electric field and can boost the short-circuit current while lowering the dark current by reflecting the minority carriers. As a result of the BSF layer’s inclusion, the solar cell’s surface recombination rate decreases, and the performance enhances.⁶⁴ 

The effect of the CIGS absorber thickness on the performance of the FTO/ZnSe/CIGS/V₂O₅/Cu model has been illustrated in Fig. 3(b). When the CIGS absorber thickness has been enhanced from 0.1 to 3 µm, J_SC, FF, and PCE follow an upward trend like before, while V_OC follows a downward trend. In addition, after 1 µm optimum absorber thickness, the PCE remains almost unchanged in this model. With an additional BSF layer, even a small valence band offset between the absorber and BSF layer may cause a barrier for the photogenerated carriers to reach the electrodes; hence, V_OC slightly decreased from ∼0.93 to ∼0.87 V with increasing absorber thickness.⁶⁵ The conventional model without a V₂O₅ BSF layer has gained a V_OC, J_SC, and PCE of 0.7 V, 35.48 mA/cm², and 19.46%, respectively, with a 1 µm thick absorber. However, after adding a 0.05 µm thick V₂O₅ BSF layer, the modified model has attained a V_OC, J_SC, and PCE of 0.898 V, 41.34 mA/cm², and 31.86%, respectively, for the same 1 µm CIGS absorber thickness, showcasing a significant increase in performance. The J_SC and V_OC parameters have shown an almost similar increasing tendency in the previous studies.^29,66,67 The key explanation behind this augmentation of PCE is that V₂O₅ and CIGS both function as absorbers, having a 1.05 µm combined thickness, and the V₂O₅ BSF layer is helping to improve the photon energy absorption of the solar cell.⁴⁵ As a result, a huge number of photons can be absorbed, and more electron–hole pairs are created. All these actions significantly boost the PV performance of the modified model over the conventional design.⁶⁸ 

One of the main reasons behind choosing V₂O₅ as a BSF layer is because it has high electron mobility; hence, it can effectively transport electrons from the back surface of the solar cell to the front surface, where they can be collected by the electrodes. This can help increase the J_SC of the solar cell. In addition, V₂O₅ has a high dielectric constant; therefore, it can effectively store electrical charge, which can help increase the device’s V_OC. As V₂O₅ also has a wide bandgap, it can effectively block the recombination of electrons and holes at the back surface of the solar cell. This can help boost the device’s efficiency by reducing the number of electrons and holes that are lost at the back surface of the PV cell. Furthermore, V₂O₅ is an earth-abundant material, and its deposition process is relatively simple and low-cost.⁴⁷ In and Ga are the CIGS-based solar cells’ high-priced components. Therefore, using a very thick CIGS absorber is not advised. The quantity of Ga and In needed to produce these devices is equivalently decreased by reducing the thickness of the CIGS material, which lowers the overall cost of manufacturing such devices. V₂O₅ is less expensive and more accessible than Ga- and In-based semiconductors, and also, the results of this work demonstrate that the updated model is more efficient than the original design. As a result, the findings of this study might point manufacturers in the direction of more lucrative CIGS-based solar cell production. The influence of absorber thickness on the hole–electron carrier concentration and total generation-recombination is shown in Figs. 3(c)–3(f).

When the ZnSe buffer layer thickness has been varied between 0.05 and 0.3 µm, its effect on the performance of both conventional and modified devices is as illustrated in Fig. 3(b). The impact of the modification of the ZnSe buffer layer thickness is less significant for both with and without the BSF layer models. However, for both models, the increase in the thickness of the ZnSe buffer layer slightly reduces J_SC and PCE. This is because when the electron transport layer (ETL) thickness is greater, fewer photons can reach the absorber layer; this reduces the formation of electron–hole pairs (EHPs) due to the parasitic absorption by the ETL itself.³² The optimum thickness of the ZnSe buffer layer can be considered as 0.05 µm, the same as the initial value, for both models as it gives the best performance.

The acceptor density (N_A) of the CIGS absorber layer has been adjusted from 1 × 10¹² to 1 × 10²⁰ cm⁻³ for both conventional and modified devices to see how it affects the device performance, and the observed trends are shown in Fig. 4(a). For this scenario, the acceptor density of V₂O₅ is 1 × 10¹⁹ cm⁻³, while the donor densities of ZnSe and FTO layers are held constant at 1 × 10¹⁸ and 1 × 10²² cm⁻³, respectively. In the modified model, when increasing N_A of the CIGS absorber from 1 × 10¹² to 1 × 10²⁰ cm⁻³, the V_OC increases from 0.79 to 1.03 V. However, from 1 × 10¹² to 1 × 10¹⁸ cm⁻³ N_A of the CIGS absorber, J_SC is nearly constant, ` when the absorber N_A has been enhanced from 1 × 10¹⁸ to 1 × 10²⁰ cm⁻³, J_SC drastically declines from 41.34 to 1.31 mA/cm². V_OC and J_SC have followed these trends because the recombination process is augmented by the higher absorber N_A, which reduces the collection probability of the photo-generated carriers.³² Again, from 1 × 10¹² to 1 × 10¹⁸ cm⁻³ N_A of the CIGS absorber, the FF increases from 78.26% to 85.8%, but after that, it declines suddenly. The PCE is contingent upon V_OC, J_SC, and FF,³² and from 1 × 10¹² to 1 × 10¹⁸ cm⁻³ N_A of the absorber, the PCE increases from 25.39% to 31.86%, and at 1 × 10¹⁹ and 1 × 10²⁰ cm⁻³ N_A, the PCE drops to 4.25% and 0.76%, respectively. Hence, the initially taken 1 × 10¹⁸ cm⁻³ N_A of the absorber can be considered as the optimum value for the model with the BSF layer. On the other hand, without the BSF layer, almost similar trends have been observed, and the same as before, the maximum PCE has been found at 1 × 10¹⁸ cm⁻³ carrier concentration. The effect of absorber N_A on the hole–electron carrier concentration and total generation-recombination is shown in Figs. 4(c)–4(f).

The absorber defect density has been modulated from 10¹² to 10¹⁸ cm⁻³, and Fig. 4(b) depicts its impact on the PV properties of the devices with and without the BSF layer. The enhancement of the CIGS defect density has resulted in a significant reduction in the V_OC, J_SC, FF, and PCE in both structures, which is because of the Shockley–Read–Hall (SRH) recombination. As a result, carrier recombination, lifetime reduction, and device performance declination occur.³² In the modified model, the PCE drops steadily with increasing absorber defect density. Moreover, the maximum PCE has been observed when the absorber defect density is 10¹² cm⁻³. However, too low absorber defect density is impractical, so the optimum absorber defect density has been set to 10¹⁴ cm⁻³, which is the same as the initial value. On the other hand, in the base model, the PCE remains almost constant from 10¹² to 10¹⁶ cm⁻³ absorber defect density, and after that, it declines rapidly. The physics behind the effect of defects in CIGS (copper indium gallium selenide) material is related to the electronic properties of the material. Defects in CIGS can affect the electronic properties of the material in several ways, including the bandgap, the recombination rate of electrons and holes, and the mobility of charge carriers.

One of the main types of defects in CIGS is point defects, which are defects that occur at a single point in the material. Point defects can be either intrinsic, such as vacancies and interstitials, or extrinsic, such as impurities. Intrinsic point defects can affect the electronic properties of the material by changing the recombination rate of electrons and holes, which can lead to a decrease in the open-circuit voltage of the solar cell. Extrinsic point defects can affect the electronic properties of the material by introducing impurities into the material, which can change the bandgap and affect the mobility of charge carriers.

Another type of defect in CIGS is extended defects, which are defects that occur over a larger area of the material. Extended defects can include dislocations, twin boundaries, and grain boundaries. These types of defects can affect the electronic properties of the material by reducing the mobility of charge carriers, which can lead to a decrease in the short-circuit current of the solar cell. In addition, extended defects can act as recombination centers for electrons and holes, which can also lead to a decrease in the open-circuit voltage of the solar cell.

In summary, the physics behind the effect of defects in CIGS material is related to the electronic properties of the material. Defects can affect the electronic properties of the material by changing the recombination rate of electrons and holes, changing the bandgap, and reducing the mobility of charge carriers. These effects can lead to a decrease in the performance of CIGS solar cells.⁶⁹ The effect of hole–electron carrier concentration and total generation-recombination concerning the absorber layer defect density is shown in Fig. 5.

The impact of the defect densities at the V₂O₅/CIGS and CIGS/ZnSe interfaces of the modified model has been shown in Figs. 6(a) and 6(b), respectively. When the interfacial defect density increases, the device performance drops as the interfacial traps at the high-level act as the recombination centers that increase the shunt resistance.³² As the interfacial defect density at the V₂O₅/CIGS interface has been varied from 10¹⁰ to 10¹⁸ cm⁻², V_OC, J_SC, FF, and PCE decrease from 0.898 to 0.751 V, 41.34 to 35.61 mA/cm², 85.8% to 78.97%, and 31.86% to 21.13%, respectively. For the same variation in the interfacial defect density at the CIGS/ZnSe interface, V_OC decreases from 0.898 to 0.569 V, J_SC remains almost constant at 41.3 mA/cm², FF decreases from 85.8% to 64.48%, and PCE decreases from 31.86% to 15.39%. The optimum interfacial defect density for both interfaces has been kept constant at 10¹⁰ cm⁻². The effect of hole–electron carrier concentration and total generation-recombination concerning the absorber layer and BSF interface defect density is shown in Figs. 6(c)–6(f). A solar cell’s interface between various layers, such as the interface between the absorber layer and the back contact, is susceptible to interfacial flaws. These flaws have the potential to function as recombination centers, which means they can promote the recombination of electrons and holes. The solar cell’s open-circuit voltage may drop as a result, and the overall efficiency of the cell may also decline. At the junction of the absorber layer and the window layer, interfacial flaws can also develop. These flaws have the potential to function as recombination centers, which means they can promote the recombination of electrons and holes. Due to this, the solar cell’s short-circuit current and voltage may both decrease. This may result in a reduction in the solar cell’s short-circuit current as well as a reduction in the cell’s overall efficiency. Through Auger recombination, which happens when an electron and a hole recombine and release their energy, driving an electron from the valence band to the conduction band, interfacial imperfections can also boost the rate of electron and hole recombination. As a result of serving as recombination sites and speeding up recombination through Auger recombination, interfacial imperfections can significantly affect the recombination rate of electrons and holes in a solar cell. This may result in a decrease in the solar cell’s open-circuit voltage and short-circuit current, as well as a decrease in the cell’s overall efficiency.⁵⁶ 

The quantum efficiency (QE) of a solar cell or other light-sensitive device is a measurement of how well it converts absorbed light into electrical current. Internal quantum efficiency (IQE) and external quantum efficiency are the two different methods of quantum efficiency analysis (EQE). The external quantum efficiency (EQE) is a measurement of the number of electrons that can be extracted from a PV device per incident number of photons, whereas the quantum efficiency (QE) value of a solar cell specifies how much current the PV cell can generate when exposed to photons of a specific wavelength.⁷⁰ Because a thicker absorber layer collects more photons, the QE of the device increases with increasing absorber thickness. Every material has a particular wavelength range of photons that it can absorb.³² At a certain wavelength, all the QE curves begin to decline toward zero at the band edge of 1.16 eV. Figure 7 shows the QE curves at a wavelength range of 300 (∼4.14 eV) to 1200 (∼1.16 eV) nm of the base CIGS and modified structures at a different absorber thickness of 0.1–2 µm without and with the BSF layer. In comparison to the base structure, it is apparent that the modified structure shows superior QE and spectral response throughout the whole wavelength range for the same absorber thickness. Especially at higher wavelengths, the modified structure with the BSF layer exhibits greater light absorption. Internal quantum efficiency (IQE) is a metric used to assess how effectively solar cells convert absorbed light into internal electrical current. It is described as the quantity of electrons produced to the quantity of photons absorbed. IQE is a measurement of the solar cell’s inherent performance and is unaffected by outside variables such as reflection or transmission losses.

In this work, the impact of the series resistance (R_s) and shunt resistance (R_sh) on the performance of the conventional and modified model has been investigated. The front and rear metallic resistance, bulk resistance, and circuit terminal resistance contribute to R_s.⁶⁷ The main consequence of R_s is to reduce FF, which means that an FF of 100% is impossible to obtain.⁷¹ V_OC and J_SC are also affected by the resistance values. To improve the PCE, lower R_s, and higher R_sh values are desirable. At first,R_sh is set at 10⁵ Ω cm², and the value of R_s is varied from 0 (ideal situation) to 6 Ω cm². Figure 8(a) shows the impact of adjusting the R_s on the conventional and modified PV model. It can be observed for the modified model that increasing R_s reduces the solar cell’s PCE considerably, similar to the findings in the literature.^26,67 While altering the R_s across the specified range, the PCE declines significantly from 31.85% to 22.65%. Similarly, in the base model, FF and PCE decrease continuously when R_s are increased, while V_OC and J_SC remain almost constant.

Now, the value of R_sh is adjusted from 10 to 1 × 10⁷ Ω cm² by setting R_s to 0.5 Ω cm². Figure 8(b) depicts the effects of adjusting the R_sh value on the modified and conventional device. When the value of R_sh of the modified device is increased, the PCE increases from 4.07% to 31.07%. In addition, V_OC, FF, and J_SC improve with increasing R_sh. Furthermore, the performance parameters of the device without the BSF layer also follow a similar trend.

Figures 10(a)–10(c) depict the current–voltage (J–V) characteristic curves of (a) various absorber layer thicknesses, (b) various doping concentrations, and (c) the optimized value of the base model and suggested model. The configuration with the BSF layer shows superior performance compared to the configuration without the BSF layer.

Materials such as MoSe₂, SnS, SnSe₂, Si, BaSi₂, and others have been studied theoretically and practically as the BSF layer of the CIGS-based solar cells. Table II shows the favorable effect of using a V₂O₅ BSF in CIGS-based solar cells, as well as a comparison of similar structures. The V₂O₅ BSF shows excellent performance compared to the other BSF layers. Because of the higher bandgap (2.2 eV) of the V₂O₅ BSF layer, it may assist the device to operate at a higher operating temperature, and also, its performance should be better than that of other BSF materials. Furthermore, based on the results reported in this work and the comparison shown in Table II, V₂O₅ may be chosen as the optimum material for CIGS-based TFSCs’ BSF layer.

The output parameters of a number of experimental and theoretical CIGS-based PV devices are presented in Table III, where the proposed model has been compared with other CIGS-based solar cells. It is noticeable from Table III that the proposed model, with a 1 µm thick CIGS absorber, can be commercially feasible compared to the other CIGS-based models by lowering the price of the absorber material. A CIGS-based solar cell illustrated an experimental PCE of 23.85%, while another showed a theoretical PCE of 26.24% with an 8 µm thick absorber. In this work, only a 1 µm thick CIGS absorber can give 31.86% efficiency, where the thickness of the V₂O₅ BSF layer is only 0.05 µm.

CIGS-based solar cells with potential V₂O₅ BSF and ZnSe buffer layers have been investigated using the SCAPS 1-D simulator. The optimum thickness, doping concentration, and defect density of the CIGS absorber were found at 1 µm, 10¹⁸, and 10¹⁴ cm⁻³, respectively, with a ZnSe buffer layer thickness of 0.05 µm and interfacial defect density of 10¹⁰ cm⁻² for the both ZnSe/CIGS and CIGS/V₂O₅ interfaces. The insertion of a thin, 0.05-µm V₂O₅ BSF layer with the FTO/ZnSe/CIGS(1-µm)/(0.05-µm)V₂O₅/Cu structure offers an improved PCE of 31.86%, which was 18.67% more. Furthermore, simulations have been conducted for determining the effect of series and shunt resistance and operating temperature on the performance of the PV cell. The PCE largely impacted by the working temperature and series resistance increased with a significant decrease in the cell performance to ∼20% from ∼31.0%. Thus, a thin CIGS-absorber layer with potential V₂O₅ BSF and ZnSe buffer layers shows huge potential for manufacturing an efficient, environmentally benign, cost-effective thin-film solar cell for practical applications in the near future.

The authors are thankful to Marc Burgleman and his colleagues at the University of Electronics and Information Systems (ELIS), Department of Electronics and Information Systems, Belgium, for supplying the SCAPS software package, version 3.3.07.

Dr. Md. Ferdous Rahman was partially supported by a special allocation project from the Ministry of Science and Technology, Government of the People’s Republic of Bangladesh [Grant No. SRG-222381(EAS) (2022–2023)].

The authors have no conflicts to disclose.

Md. Ferdous Rahman: Conceptualization (equal); Data curation (equal); Formal analysis (equal); Funding acquisition (equal); Investigation (equal); Methodology (equal); Project administration (equal); Resources (equal); Software (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Nayeem Mahmud: Software (equal); Writing – original draft (equal); Writing – review & editing (equal). Intekhab Alam: Writing – review & editing (equal). Md Hasan Ali: Writing – review & editing (equal). M.M.A. Moon: Writing – review & editing (equal). Abdul Kuddus: Writing – review & editing (equal). G.F. Ishraque Toki: Writing – review & editing (equal). Md. Abdullah Al Asad: Writing – review & editing (equal). M. Khalid Hossain: Formal analysis (equal); Resources (equal); Software (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). M. H. K. Rubel: Writing – review & editing (equal).

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