Solar-cell collection efficiency and its variation with voltage

Internal collection efficiency of solar cells is calculated as a function of depletion width, minority-carrier diffusion length, solar spectrum, and absorption coefficient. Particular attention is given to the variation of depletion width with voltage, which may reduce collection efficiency by a few percent at operating voltages and may be misinterpreted as a shunting effect. Calculations of collection-efficiency magnitude and voltage dependence, plus comparisons with experiment, are presented for several types of solar cells. Primary emphasis is placed on polycrystalline thin-film cells with relatively short diffusion lengths and hence potentially more pronounced collection efficiency effects.