knjiga solarna energija dobra

596 Cu(InGa)Se 2 SOLAR CELLS
Current
[mA/cm 2 ]
20
0
a
b
c
x
0
E g [eV]
1.02
0.24 1.16
0.61 1.40
a b c
−20
−40
−0.3 0.0 0.3 0.6 0.9
Voltage
[V]
Figure 13.16 Current–voltage curves for Cu(InGa)Se 2 /CdS solar cells with different relative Ga
content giving (a) E g = 1.02, (b) 1.16, and (c) 1.4 eV
1.0
Energy
[eV]
3.0 2.0 1.5
1.0
0.8
Quantum efficiency
0.6
0.4
0.2
c b a
0.0
400 600 800 1000 1200 1400
Wavelength
[nm]
Figure 13.17 Quantum efficiency curves for the devices shown in Figure 13.16
To understand the specific diode behavior of Cu(InGa)Se 2 /CdS solar cells, it is
instructive to look at the effect of the Cu(InGa)Se 2 band gap, varied by changing x ≡
Ga/(In + Ga), and temperature. Figures 13.16 and 13.17 show J –V and QE curves for
3 devices with x = 0, 0.24, and 0.61, corresponding to E g = 1.02, 1.16, and 1.40 eV,
respectively. V OC increases and the position of the long-wavelength QE edge shifts to
greater energy as E g increases. Figure 13.18 shows the temperature dependence of V OC for
these devices. In each case, as T → 0, V OC → E g /q. Thus, combining equations (13.7)