High-Efficiency Thin-Film Silicon Solar Cells in Triple Junction

High-Efficiency Thin-Film Silicon Solar Cells in Triple Junction

High-Efficiency Thin-Film Silicon Solar Cells
in Triple Junction Configuration
J.-W. Schüttauf, M. Stuckelberger, S. Hänni, E. Moulin, B. Niesen, F.-J. Haug, F. Meillaud and C. Ballif
Ecole Polytechnique Fédérale de Lausanne (EPFL), Institute of Microengineering (IMT),
Photovoltaics and thin-film electronics laboratory, Rue Maladière 71b, CH-2000 Neuchâtel, Switzerland
Tandem and Triple solar cells
Glass
Glass
Amorphous top cell
n-type a-Si:H
Microcrystalline
middle cell
Int. reflector layer (IRL)
p-type µc-Si:H
Low energy pay-back time of less than 1 year
intrinsic µc-Si:H
Proven reliability >20 years
n-type µc-Si:H
p-type µc-Si:H
All raw materials are abundant and non-toxic
n-type a-Si:H
middle
Amorphous top cell
Low material use (< 2 µm silicon)
top
intrinsic a-Si:H
p-type a-Si:H
intrinsic a-Si:H
Established manufacturing technology
p-type a-Si:H
ZnO
ZnO
top
Thin Film Silicon
=> attractive for large scale deployment
Microcrystalline
bottom cell
intrinsic µc-Si:H
n-type µc-Si:H
Material quality requires thin devices
Microcrystalline
bottom cell
Low absorption coefficient (indirect bandgap)
intrinsic µc-Si:H
bottom
bottom
p-type µc-Si:H
ZnO
=> typical cell thickness below absorption length
n-type µc-Si:H
Design rule: summed current density ≈ 30 mA/cm2
ZnO
- Matched tandem with ≈ 15 mA/cm2 (difficult for a-Si top)
Reflector
- Matched triple with ≈ 10 mA/cm2 (no IRL, similar complexity)
Reflector
Light scattering ZnO substrates
Solar cell performance
Textured front contact of ZnO grown by LP-CVD
1.0
7 mins
15 mins
30 mins
EQE
0.8
Smooth ZnO: good growth template,
=> high Voc and fill factor
Current density (mA/cm )
Rough ZnO: good light scattering
=> high current density
INITIAL
0.6
0.4
0.2
15 min
7 min
30 min
0.0
400
500
600
700
800
900
1000
INITIAL
2
Ar plasma converts from rough to smooth texture
2
0
7 mins
15 mins
30 mins
-2
-4
-6
-8
-10
-0.5
1100
0.0
0.5
1.0
1.5
2.0
2.5
Voltage (V)
Wavelength (nm)
Ar plasma
t (mins)
7
Voc (V)
FF (%)
Jsc, top
Jsc, mid Jsc, btm Jsc, sum Stable eff
(mA/cm2) (mA/cm2) (mA/cm2) (mA/cm2)
(%)
10.1
9.8
10.1
30.1
13.5
1.87
73.6
15
1.89
74.4
10.0
9.8
9.8
29.5
13.7
30
1.91
77.4
9.7
8.7
9.5
27.9
12.8
Trend
1.90
1.0
STABLE
0.8
EQE
1.80
FF (%)
7 mins
15 mins
30 mins
75
Current density (mA/cm )
1.85
2
0.6
0.4
0.2
2
Jsc (mA/cm )
70
10.0
0.0
9.5
initial stable
top
mid
btm
9.0
400
500
600
700
800
900
1000
STABLE
2
Voc (V)
1.95
0
-2
7 mins
15 mins
30 mins
-4
-6
-8
-10
1100
-0.5
0.0
0.5
1.0
1.5
2.0
Voltage (V)
Wavelength (nm)
Efficiency (%)
8.5
Ar plasma
t (mins)
7
Voc (V)
FF (%)
1.84
71.4
12.5
15
1.85
72.5
9.7
9.6
9.6
28.9
12.8
12.0
30
1.86
76.1
9.3
8.6
9.4
27.3
12.2
13.5
initial
stable
13.0
10
20
Jsc, top
Jsc, mid Jsc, btm Jsc, sum Stable eff
(mA/cm2) (mA/cm2) (mA/cm2) (mA/cm2)
(%)
10.1
9.5
9.9
29.5
12.5
30
Plasma treatment time (min)
J.W Schüttauf et al., IEEE J. of PV, 2014
Conclusions
Ar plasma is used to modify the light scattering of textured ZnO films
A Summed current density >30 mA/cm2 is demonstrated
High-efficiency triple cells in p-i-n configuration reach 13.5 %, they stabilize at 12.8 % after 1000 h light soaking
Financial support by OFEN under project SI/500750-01, CCEM-CH and by CTI under project Trigger 13333.1 is gratefully acknowledged.
A part of this work was carried out in the framework of the FP7 project “Fast Track”, funded by the EC under grant agreement no 283501.