Thin film polycrystalline silicon solar cells. Quarterly report No. 1, January 1, 1979-March 31, 1979

Abstract

A theory capable of predicting the performance of polycrystalline silicon solar cells is formulated. It relates grain size to mobility, lifetime, diffusion length, reverse saturation current, open circuit photovoltage and fill factor. Only the diffusion lengths measured by the surface photovoltage technique for grains less than or equal to 5 ..mu..m do not agree with our theory. The reason for this discrepancy is presently being investigated. It is concluded that grains greater than or equal to 100 ..mu..m are necessary to achieve efficiencies greater than or equal to 10% at AM1 irradiance. The calculations were performed for the case of no grain boundary passivation. The parameters that best fit the available data are found to be: (1) number of surface states at grain boundaries acting as recombination centers = 1.6 x 10/sup 13//cm/sup 2/; (2) capture cross section = 2 x 10/sup -16/ cm/sup 2/; (3) surface recombination velocity at grain boundary = 3.2 x 10/sup 4/ cm/sec. The following types of solar cells are considered in the model: SnO/sub 2//Si Heterostructure, MIS, and p/n junction. In all types of solar cells considered, grain boundary recombination plays a dominant role, especially for small grains. Though the calculations were originally expectedmore » to yield only order of magnitude results, they have proven to be accurate for most parameters within 10%.« less