Automated measurement of the carrier collection length in a-Si:H solar cells

A phenomenological model for fitting a-Si:H solar cell I-V curves using the dependence of photogenerated carrier collection efficiency on bias is proposed. An expression for the collection efficiency based on Crandall's model, taking the P+/i interface recombination into account, is adopted for fitting I-V curves measured under actual solar-cell illumination conditions. Current and voltage are determined by an automated measurement system, and the I-V curves are fitted by the Marquardt method. The carrier collection length can be calculated automatically from the fitting results. The fitting errors are compared to those obtained by J. Smeets et al. (Technical Digest of International PVSEC-3, p.601, 1987). Good agreement between the two sets of results is found.