Study of the type inversion of the semiconductor in irradiated solar cells

Abstract

Solar cells, used for space applications, are exposed to energetic particles such as protons and electrons. These energetic particles induce severe degradation on the performance of solar cells. This degradation is usually attributed to lattice damage in the active region of the solar cell. One of the phenomena observed in Silicon solar cells exposed to 1 MeV electron irradiation is the anomalous degradation of the short circuit current (Jsc). It initially decreases followed by a recovery before falling again with increasing electron fluence. This behaviour is usually attributed to type inversion of the semiconductor inthe solar cell active region. In order to elucidate this behaviour , a numerical simulation using SCAPS software is carried out. The current voltage (J-V) characteristics of a Si n+-p-p+ structure are calculated under AM0 spectrum with the fluence of 1MeV electrons as a variable parameter. The effect of irradiation on the solar cell is simulated by a set of defects of which the energy levels lie deep in energy gap of Silicon. Although several types of deep levels are induced by irradiation including deep donors,deep acceptors, and generation recombination centres. It was found that the shallower donor trap is responsible for this behaviour and this not related to type in version but to a lateral widening of the space charge region. It is also found that solar cells with smaller thickness have better radiation tolerance.