Theoretical study of the photovoltaic properties of polycrystalline silicon

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Abstract
By considering the variation of grain-boundary space-charge potential barrier height with grain size and doping level, the dependence of polysilicon solar cell parameters on the grain size (d) and substrate resistivity have been theoretically investigated. A new relation is presented for the effective diffusion length of minority carriers in polysilicon which predicts that the effective diffusion length is approximately proportional to dr, where r varies from 0 to 1. Computations show that, as base resistivity decreases, the effect of the grain-boundary recombination process increases, and consequently the polysilicon cell parameters do not vary with resistivity in the same manner as has been observed for a single-crystal cell. Our theory predicts also the dominance of shunting effects of grain boundary at small grain sizes or low base resistivities. The available experimental data are found to be in good agreement with the predictions of the theory.