Page 63 - Applied Photovoltaics
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§ E g0 ·
Ȗ
I 0 BT exp ¨ ¨ ¸ ¸ (3.10)
© kT ¹
where B is independent of temperature, E g0 is the linearly extrapolated zero
temperature bandgap of the semiconductor making up the cell (Green, 1992) and Ȗ
includes the temperature dependencies of the remaining parameters determining I 0 .
The short circuit current (I sc ) increases with temperature, since the bandgap energy
(E g ) decreases and more photons have enough energy to create e-h pairs. However,
this is a small effect. For silicon
1 dI sc | . 0 0006 q C 1 (3.11)
I sc dT
The main effect of increasing temperature for silicon solar cells is a reduction in V oc ,
the fill factor and hence the cell output. These effects are illustrated in Fig. 3.9.
Figure 3.9. The effect of temperature on the I-V characteristics of a solar cell.
The temperature dependency of V oc and FF for silicon is approximated by the
following equations:
dV oc > V g 0 V oc Ȗ q kT @ | 2 mV/q C (3.12)
dT T
1 dV oc | . 0 003 q C 1 (3.13)
V oc dT
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