Optical generation rate of electron-hole pairs in multilayer thin-film photovoltaic cells

Abstract

A technique for calculating the optical generation rate of electron-hole pairs (EHPs) in the absorber layers of a multilayer photovoltaic cell is described, taking into account the multiple internal reflections that typically occur in such multilayer cells. The technique is based on the assumption that all multiply reflected and transmitted light, within the cell, combines incoherently and enables the determination of the EHP generation rate at every position within the absorber layers. This, in turn, yields the optical generation rate profile - a quantity that is needed in one-dimensional computer simulations of solar cells. Calculations pertaining to a typical a-Si:H-based solar cell indicate that ignoring the effect of front layers, such as glass and transparent conducting oxides (TCOs), has a significant effect on the calculated optical generation rate profile. Also, calculations suggest that the TCO in a typical glass/TCO/a-Si:H solar cell should have a real refractive index of ~2.0, in good agreement with the observed fact that ZnO is a good TCO for these types of cells.