Simplified device simulation of silicon solar cells using a lumped parameter optical model

An optical model for solar cell device simulations providing a computational rapid alternative or extension to ray tracing is presented. Its lumped input parameters are mainly the wavelength-dependent external front surface transmission T_ext and pathlength enhancement Z, which can be derived by measurements and/or ray tracing of finished devices. A way to calculate the generation profile G from those inputs is described, showing negligible error for typical silicon solar cell properties compared to G from ray tracing. Including a recently proposed parameterization of Z, it is shown that the lumped input parameters are, to good approximation, independent of 1) the incident spectrum, 2) the device thickness, and 3) the device temperature. The latter mainly assumes that the temperature influence of the silicon bulk dominates over the thin film's one, which is shown experimentally for a few typical thin-film materials. The model is successfully applied to accurately predict optical characteristics of high efficiency laboratory solar cells with two different thicknesses and temperatures. It is thus useful to simplify and speed up optical modeling relative to ray tracing alone, without significant error for typical silicon solar cell properties.