Surface passivation is essential for high-efficiency crystalline silicon (c-Si) solar cells. Despite the common use of transparent conductive oxides (TCOs) in the field of solar cells, obtaining surface passivation by TCOs has thus far proven to be particularly challenging. In this work, we demonstrate outstanding passivation of c-Si surfaces by highly transparent conductive ZnO films prepared by atomic layer deposition. Effective surface recombination velocities as low as 4.8 cm/s and 11 cm/s are obtained on 3 Ω cm n- and p-type (100) c-Si, respectively. The high levels of surface passivation are achieved by a novel approach by using (i) an ultrathin SiO2 interface layer between ZnO and c-Si, (ii) a sacrificial Al2O3 capping layer on top of the ZnO film during forming gas annealing, and (iii) the extrinsic doping of the ZnO film by Al, B, or H. A combination of isotope labeling, secondary-ion mass spectrometry, and thermal effusion measurements showed that the sacrificial Al2O3 capping layer prevents the effusion of hydrogen from the crystalline ZnO and the underlying Si/SiO2 interface during annealing, which is critical in achieving surface passivation. After annealing, the Al2O3 capping layer can be removed from the ZnO film without impairing the high levels of surface passivation. The surface passivation levels increase with increased doping levels in ZnO, which can be attributed to field-effect passivation by a reduction in the surface hole concentration. The ZnO films of this work are suitable as a transparent conductor, an anti-reflection coating, and a surface passivation layer, which makes them particularly promising for simplifications in future solar cell manufacturing.

1.
W.
Shockley
and
W. T. J.
Read
, “
Statistics of the recombinations of holes and electrons
,”
Phys. Rev.
87
(
5
),
835
842
(
1952
).
2.
R. N.
Hall
, “
Electron-hole recombination in germanium
,”
Phys. Rev.
87
,
387
(
1952
).
3.
L. E.
Black
,
B. W. H.
van de Loo
,
B.
Macco
,
J.
Melskens
,
W. J. H.
Berghuis
, and
W. M. M.
Kessels
, “
Explorative studies of novel silicon surface passivation materials: Considerations and lessons learned
,”
Sol. Energy Mater. Sol. Cells
188
,
182
189
(
2018
).
4.
G.
Krugel
,
A.
Sharma
,
W.
Wolke
 et al, “
Study of hydrogenated AlN as an anti-reflective coating and for the effective surface passivation of silicon
,”
Phys. Status Solidi—Rapid Res. Lett.
7
(
7
),
457
460
(
2013
).
5.
B.
Liao
,
B.
Hoex
,
A. G.
Aberle
 et al, “
Excellent c-Si surface passivation by low-temperature atomic layer deposited titanium oxide
,”
Appl. Phys. Lett.
104
(
25
),
253903
(
2014
).
6.
T. G.
Allen
and
A.
Cuevas
, “
Electronic passivation of silicon surfaces by thin films of atomic layer deposited gallium oxide
,”
Appl. Phys. Lett.
105
(
2014
),
31601
(
2014
).
7.
Y.
Wan
,
J.
Bullock
, and
A.
Cuevas
, “
Tantalum oxide/silicon nitride: A negatively charged surface passivation stack for silicon solar cells
,”
Appl. Phys. Lett.
106
(
20
),
201601
(
2015
).
8.
J.
Cui
,
Y.
Wan
,
Y.
Cui
 et al, “
Highly effective electronic passivation of silicon surfaces by atomic layer deposited hafnium oxide
,”
Appl. Phys. Lett.
110
(
2)
,
021602
(
2017
).
9.
L. E.
Black
and
W. M. M.
(Erwin)
Kessels
, “
POx/Al2O3 stacks: Highly effective surface passivation of crystalline silicon with a large positive fixed charge
,”
Appl. Phys. Lett.
,
112
(
20
),
201603
(
2018
).
10.
B.
Macco
,
L. E.
Black
,
J.
Melskens
 et al, “
Atomic-layer deposited Nb2O5 as transparent passivating electron contact for c-Si solar cells
,”
Sol. Energy Mater. Sol. Cells
184
(
April
),
98
104
(
2018
).
11.
Y.
Wan
,
J.
Bullock
,
M.
Hettick
 et al, “
Zirconium oxide surface passivation of crystalline silicon
,”
Appl. Phys. Lett.
112
(
20
),
201604
(
2018
).
12.
Y.
Wu
,
P. M.
Hermkens
,
B. W. H.
van de Loo
 et al, “
Electrical transport and Al doping efficiency in nanoscale ZnO films prepared by atomic layer deposition
,”
J. Appl. Phys.
114
(
2
),
24308
(
2013
).
13.
D.
Garcia-Alonso
,
S. E.
Potts
,
C. A. A.
van Helvoirt
 et al, “
Atomic layer deposition of B-doped ZnO using triisopropyl borate as the boron precursor and comparison with Al-doped ZnO
,”
J. Mater. Chem. C
3
(
13
),
3095
3107
(
2015
).
14.
B.
Macco
,
D.
Deligiannis
,
S.
Smit
 et al, “
Influence of transparent conductive oxides on passivation of a-Si:H/c-Si heterojunctions as studied by atomic layer deposited Al-doped ZnO
,”
Semicond. Sci. Technol.
29
(
12
),
122001
(
2014
).
15.
N.
Nandakumar
,
B.
Hoex
,
B.
Dielissen
 et al, “
Conductive gallium-doped ZnO films deposited by ultrafast spatial atomic layer deposition for photovoltaic application
,”
in
25th Asia Photovoltaic Solar Energy Conference and Exhibition
(
2015
).
16.
B.
Macco
,
H. C. M.
Knoops
,
M. A.
Verheijen
 et al, “
Atomic layer deposition of high-mobility hydrogen-doped zinc oxide
,”
Sol. Energy Mater. Sol. Cells
173
,
111
119
(
2017
).
17.
R.
Peibst
,
Y.
Larionova
,
S.
Reiter
 et al, “
Building blocks for industrial, screen-printed double-side contacted POLO cells with highly transparent ZnO:Al layers
,”
IEEE J. Photovoltaics
8
(
3
),
719
725
(
2018
).
18.
K.
Kajiyama
and
Y.
Furukawa
, “
Electrical and optical properties of SnO2-Si heterojunctions
,”
Jpn. J. Appl. Phys.
6
,
905
606
(
1967
).
19.
P.
Stradins
,
S.
Essig
,
W.
Nemeth
 et al, “
Passivated tunneling contacts to n-type wafer silicon and their implementation into high performance solar cells preprint
,” in
6th World Conference on Photovoltaic Energy Conversion
,
Kyoto, Japan
,
23–27 November 2014
(NREL,
2014
).
20.
F.
Wang
,
S.
Zhao
,
B.
Liu
 et al, “
Silicon solar cells with bifacial metal oxides carrier selective layers
,”
Nano Energy
39
,
437
443
(
2017
).
21.
J.
Ding
,
Y.
Zhou
,
G.
Dong
 et al., “
Solution-processed ZnO as the efficient passivation and electron selective layer of silicon solar cells
,”
Prog. Photovolt. Res. Appl.
26
,
974
980
(
2018
).
22.
S.
Smit
,
D.
Garcia-Alonso
,
S.
Bordihn
 et al, “
Metal-oxide-based hole-selective tunneling contacts for crystalline silicon solar cells
,”
Sol. Energy Mater. Sol. Cells
120
,
376
382
(
2014
).
23.
J.
Panigrahi
,
S. R.
Vandana
 et al 
Crystalline silicon surface passivation by thermal ALD deposited Al doped ZnO thin films
.
AIP Adv.
7
(
3
),
35219
(
2017
).
24.
C.
Battaglia
,
S. M.
de Nicolás
,
S.
De Wolf
 et al, “
Silicon heterojunction solar cell with passivated hole selective MoOx contact
,”
Appl. Phys. Lett.
104
(
11
),
113902
(
2014
).
25.
L. G.
Gerling
,
S.
Mahato
,
A.
Morales-Vilches
 et al, “
Transition metal oxides as hole-selective contacts in silicon heterojunctions solar cells
,”
Sol. Energy Mater. Sol. Cells
145
,
109
115
(
2016
).
26.
A.
Moldovan
,
F.
Feldmann
,
M.
Zimmer
 et al, “
Tunnel oxide passivated carrier-selective contacts based on ultra-thin SiO2 layers
,”
Sol. Energy Mater. Sol. Cells
142
,
123
127
(
2015
).
27.
S.
Lindekugel
,
H.
Lautenschlager
,
T.
Ruof
, and
S.
Reber
, “
Plasma hydrogen passivation for crystalline silicon thin-films
,” in
23rd EU-PVSEC
,
Valencia, Spain
(
2008
), pp.
2232
2235
.
28.
M. K.
Stodolny
,
M.
Lenes
,
Y.
Wu
 et al, “
n-Type polysilicon passivating contact for industrial bifacial n-type solar cells
,”
Sol. Energy Mater. Sol. Cells
158
,
24
28
(
2016
).
29.
F.
Feldmann
,
M.
Simon
,
M.
Bivour
 et al, “
Carrier-selective contacts for Si solar cells
,”
Appl. Phys. Lett.
104
(
18
),
181105
(
2014
).
30.
B.
Nemeth
,
D. L.
Young
,
M. R.
Page
 et al, “
Polycrystalline silicon passivated tunneling contacts for high efficiency silicon solar cells
,”
J. Mater. Res.
31
(
6
),
671
681
(
2016
).
31.
M.
Schnabel
,
B. W. H.
van de Loo
,
W.
Nemeth
 et al, “
Hydrogen passivation of poly-Si/SiOx contacts for Si solar cells using Al2O3 studied with deuterium
,”
Appl. Phys. Lett.
112
(
20
),
203901
(
2018
).
32.
W.
Kern
, “
Cleaning solutions based on hydrogen peroxide for use in silicon semiconductor technology
,”
RCA Rev.
31
,
187
206
(
1970
).
33.
H. C. M.
Knoops
,
B. W. H.
van de Loo
,
S.
Smit
 et al., “
Optical modeling of plasma-deposited ZnO films: Electron scattering at different length scales
,”
J. Vac. Sci. Technol. A
33
(
2
),
21509
(
2015
).
34.
A.
Richter
,
S. W.
Glunz
,
F.
Werner
 et al, “
Improved quantitative description of Auger recombination in crystalline silicon
,”
Phys. Rev. B
86
(
16
),
165202
(
2012
).
35.
K. R.
McIntosh
and
S. C.
Baker-Finch
, “
OPAL 2: Rapid optical simulation of silicon solar cells
,” in
2012 38th IEEE Photovoltaic Specialist Conference
(IEEE,
2012
), pp.
000265
000271
.
36.
X.
Yang
,
Q.
Bi
,
H.
Ali
 et al, “
High-performance TiO2-based electron-selective contacts for crystalline silicon solar cells
,”
Adv. Mater.
28
(
28
),
5891
5897
(
2016
).
37.
D. L.
Young
,
W.
Nemeth
,
S.
Grover
 et al., “
Carrier-selective, passivated contacts for high efficiency silicon solar cells based on transparent conducting oxides
,” in
2014 IEEE 40th Photovoltaic Specialist Conference
(IEEE,
2014
), Vol. 0, pp.
1
5
.
38.
X.
Yang
,
P.
Zheng
,
Q.
Bi
, and
K.
Weber
, “
Silicon heterojunction solar cells with electron selective TiOx contact
,”
Sol. Energy Mater. Sol. Cells
150
,
32
38
(
2016
).
39.
W.
Beyer
,
U.
Breuer
,
F.
Hamelmann
 et al., “
Hydrogen diffusion in zinc oxide thin films
,”
MRS Proc.
1165
,
1165-M05-24
(
2009
).
40.
G.
Dingemans
,
F.
Einsele
,
W.
Beyer
 et al, “
Influence of annealing and Al2O3 properties on the hydrogen-induced passivation of the Si/SiO2 interface
,”
J. Appl. Phys.
111
(
9
),
93713
(
2012
).
41.
K. G.
Sun
,
Y. V.
Li
,
D. B.
Saint John
, and
T. N.
Jackson
, “
pH-controlled selective etching of Al2O3 over ZnO
,”
ACS Appl. Mater. Interfaces
,
6
,
7028
7031
(
2014
).
42.
G.
Dingemans
,
W.
Beyer
,
M. C. M.
van de Sanden
, and
W. M. M.
Kessels
, “
Hydrogen induced passivation of Si interfaces by Al2O3 films and SiO2/Al2O3 stacks
,”
Appl. Phys. Lett.
97
(
15
),
152106
(
2010
).
43.
G.
Dingemans
,
C. A. A.
van Helvoirt
,
D.
Pierreux
 et al, “
Plasma-assisted ALD for the conformal deposition of SiO2: Process, material and electronic properties
,”
J. Electrochem. Soc.
159
(
3
),
H277
H285
(
2012
).
44.
E.
Burstein
, “
Anomalous optical absorption limit in InSb
,”
Phys. Rev.
93
(
3
),
632
(
1954
).
45.
T. S.
Moss
, “
The interpretation of the properties of indium antimonide
,”
Proc. Phys. Soc. B
67
(
10
),
775
782
(
1954
).
46.
K.
Ellmer
and
R.
Mientus
, “
Carrier transport in polycrystalline ITO and ZnO:Al II: The influence of grain barriers and boundaries
,”
Thin Solid Films
516
(
17
),
5829
5835
(
2008
).
47.
J.
Melskens
,
B. W. H.
van de Loo
,
B.
Macco
 et al, “
Passivating contacts for crystalline silicon solar cells: From concepts and materials to prospects
,”
IEEE J. Photovoltaics
8
(
2
),
373
388
(
2018
).
48.
B.
Macco
,
B. W. H.
van de Loo
, and
W. M. M.
Kessels
, “
Atomic layer deposition for high efficiency crystalline silicon solar cells
,” in
Atomic Layer Deposition in Energy Conversion Applications
, edited by
J.
Bachmann
(
Wiley
,
2017
).

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