Separation of bulk diffusion length and back surface recombination velocity by improved IQE-analysis

Abstract

Key parameters for the quantification of minority carrier recombination in solar cells are the effective bulk diffusion length, the bulk diffusion length and the back surface recombination velocity. As wafer thickness decreases and bulk quality increases the simultaneous determination of these parameters gains importance for cell process optimization in PV industry. Methods for obtaining these parameters have been described in the literature, such as the linear approximation on the inverse IQE vs. light penetration depth. We will formulate the limitations of this approach using numerically and experimentally determined IQE-data. The ambiguity of the older approach is solved by an improved equation, making it possible to obtain these parameters from a fit on the IQE within 820-940 nm. In addition an equation incl. the loss in the emitter is presented. Both methods are ideally suited for fast LBIC scan evaluations.