Drift fields in photovoltaic solar energy converter cells

Abstract

A theoretical investigation into the effects of electrostatic drift fields in the diffused region and in the base region of photovoltaic solar energy converter cells has been carried out. Expressions for a single-layer and a two-layer model for each of the two regions have been evolved. These expressions have been applied to the study of the semiconductor parameters in the diffused region with and without drift field. The applicability of surface recombination velocities in the normal expected range has been established, and the introduction of a drift field in the diffused region has been found to necessitate only a decrease of the minority carrier lifetime by a factor of 4.4 compared to the field free case. Further, a study of the effect of drift fields in the base region of solar cells upon the rate of their performance degradation due to nuclear particle irradiation has shown that drift fields in the base region can considerably reduce the radiation damage rate and increase the useful life of solar cells in the Van Allen belt environments by about an order of magnitude over that of present "n on p" radiation resistant silicon solar cells. Various configurations of the drift fields in the base layer, including arrangement in one and two layers with drift field, were investigated in order to find the most promising layout for the achievement of the slowest degradation rates, and to lay the groundwork for future device design work. Data for the more promising configurations are given.