I_{L} = photogenerated current density (amperes/cm^{2})
I_{o}= reverse saturation current density (amperes/cm^{2})
V_{oc}= open circuit voltage (volts)
T=temperature
Temperature affects the characteristic equation of a solar cell in two ways: directly, via T in the exponential term, and indirectly via its effect on I_{0}. (Strictly speaking, temperature affects all of the terms, but these two far more significantly than the others.) While increasing T reduces the magnitude of the exponent in the characteristic equation, the value of I_{0} increases in proportion to expT. The net effect is to reduce V_{OC} linearly with increasing temperature. The magnitude of this reduction is inversely proportional to V_{OC}; that is, cells with higher values of V_{OC} suffer smaller reductions in voltage with increasing temperature. For most crystalline silicon solar cells the reduction is about 0.50%/°C, though the rate for the highestefficiency crystalline silicon cells is around 0.35%/°C. By way of comparison, the rate for amorphous silicon solar cells is 0.200.30%/°C, depending on how the cell is made.
The amount of photogenerated current I_{L} increases slightly with increasing temperature because of an increase in the number of thermally generated carriers in the cell. This effect is slight, however: about 0.065%/°C for crystalline silicon cells and 0.09% for amorphous silicon cells.
The overall effect of temperature on cell efficiency can be computed using these factors in combination with the characteristic equation. However, since the change in voltage is much stronger than the change in current, the overall effect on efficiency tends to be similar to that on voltage. Most crystalline silicon solar cells decline in efficiency by 0.50%/°C and most amorphous cells decline by 0.150.25%/°C. The figure to the right shows IV curves that might typically be seen for a crystalline silicon solar cell at various temperatures.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License)
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