3 Solar Cells: Basics
39
Table 3.1 Bandgap energy E g of commonly used semiconductors at temperature T = 25 °C; see
also [5]
Material
Bandgap
References
Value
Nature a
Crystalline silicon (c-Si)
1.12
Indirect
[6, 7]
Hydrogenated microcrystalline silicon (µc-Si:H)
1.12
Indirect
[4]
Hydrogenated amorphous silicon (a-Si:H)
1.7–1.9 Non-direct [4]
Crystalline germanium (c-Ge)
0.67
Indirect
[6, 7]
Hydrogenated amorphous germanium (a-Ge:H)
1.1
Non-direct [4]
Hydrogenated amorphous Si-Ge alloys (a-Si,Ge:H)
1.1–1.8 Non-direct [4]
Indium arsenide
0.36
Direct
[7]
Cadmium telluride (CdTe)
1.49
Direct
[6]
Copper indium selenide CuInSe 2
1
Direct
[8]
Copper-indium-gallium-selenide (CIGS)
(Cu x In y Ga z Se 2 )
1–1.7
Direct
[8]
Kesterite {Cu 2 ZnSn(S,Se) 4 }
1–1.5
Direct
[8]
Cuprous oxide (Cu 2 O)
2
Direct
[9]
Zinc telluride (ZnTe)
2.25
Direct
[6]
Gallium arsenide (GaAs)
1.43
Direct
[6]
Pyrite (FeS 2 )
0.95
Direct
[10]
a See Sect. 3.2.2 for the description of direct, indirect and non-direct bandgaps
Conduction band
E C
Valence band
E V
hv = E
E ph =
g
E g
Fig. 3.3 Absorption of a photon when E ph = E g . Reproduced from [4] with the kind permission
of the EPFL Press
Conduction band
E C
Valence band
E
V
h > E
E ph =
g
E g
thermalisation
Fig. 3.4 Absorption of a photon when E ph > E g ; thermalisation (conversion of excess energy E ph
− E g into heat) takes place very rapidly. Reproduced from [4] with the kind permission of the EPFL
Press