Determination of effective surface recombination velocity and minority-carrier lifetime in high-efficiency Si solar cells

A mathematical analysis for minority-carrier diffusion in a solar cell base is used to extract bulk lifetime τ and effective back-surface recombination velocity S from measurements of asymptotic decay times of short-circuit current and open-circuit voltage. Since the decay times depend individually on both S and τ, it is necessary to use both current and voltage data for unique results. Experimental measurements of current and voltage transients are presented from variable base resistivity cells, γ-irradiated cells, and cells with intentionally damaged back-surface field regions. Lifetimes determined in these experiments are compared with conventional techniques. The results show that these conventional techniques yield lifetimes in serious error for cells whose diffusion lengths approach base thickness.