Extended FF and VOC Parameterizations for Silicon Solar Cells

Abstract

This work is concerned with maximal and currently obtained fill factors of crystalline silicon solar cells. Recent research activities have led to a drastically decreased recombination in the volume as well as at the surfaces and interfaces of crystalline silicon solar cells. As a result, open-circuit voltages $({{V}_{\text{OC}}})$ and fill factor $({\textit{FF}})$ values increased significantly. In order to classify how good the achieved improvements are, it is necessary to know the maximum achievable values. Unfortunately, there is no explicit expression for the ${\textit{FF}}$ in terms of other characteristic solar cell parameters. For this reason, the empirical ${\textit{FF}}_{0}$ -relation by Green is widely used to predict upper ${\textit{FF}}$ bounds for a given ${V}_{\text{OC}}$ . In order to evaluate to what extent Green's relation is a good approximation to recently obtained values, we study ${\textit{FF}}$ – ${V}_{\text{OC}}$ relations for ideal resistance-free single junction silicon solar cells limited by intrinsic recombination using state-of-the-art analytical models. The obtained upper bounds are compared with recently published record values showing that all values stay below the intrinsic limit. We provide parameterizations of ${V}_{\text{OC}}$ and ${\textit{FF}}$ as a function of sample thickness w and base dopant density ${N}_{\text{dop}}$ .