Determination of the effective diffusion length of silicon solar cells from photoluminescence

We present a method to determine the effective diffusion length Leff of silicon solar cells from photoluminescence (PL) measurements carried out under two different operating conditions. Measuring the photoluminescence emission under open circuit condition (PL-oc), where the solar cell is not contacted at all, and short circuit condition (PL-sc), where the solar cell is held at zero voltage, Leff directly follows from the ratio of the PL-oc and the PL-sc signals. Detailed knowledge about the optical properties of the experimental setup is not necessary since the optical properties cancel out completely. We explain the theoretical background of our method and derive an analytical description for the PL-oc and the PL-sc luminescence emissions. The applicability of our method is demonstrated by the comparison of effective diffusion lengths from PL measurements with values determined from the analysis of internal quantum efficiency measurements.