Diffusion length determination in solar grade silicon by room temperature photoluminescence measurements

Minority carrier lifetime (tau) and diffusion length (L) are the most important electrical parameters to qualify silicon for photovoltaic applications. Amongst the available techniques for measuring this parameter, photoluminescence has regained interest as it can be done on raw material as well as on completed solar cells in a non destructive way. Although very efficient mapping systems can provide fast information on multicrystalline samples most quantitative measurements require a calibration that is normally achieved by correlation with other techniques like photoconductance decay. In this paper, we show that L may be evaluated in a simple way from the dependence of the room temperature photoluminescence signal on the excitation beam intensity using an analytical model based on 1D carrier diffusion. Using this 1D model, the diffusion length was calculated in photovoltaic grade silicon materials without calibration by external technique. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim