Determination of minority carrier diffusion lengths in silicon solar cells from photoluminescence images

Lately a new luminescence based spatially resolved method to measure minority carrier diffusion lengths on Silicon Solar cells was introduced using Electroluminescence (EL) [1]. The idea of this method is to analyze the reabsorption-shaped form of the emitted luminescence spectrum with optical filters, enabling one to determine the depth distribution of excess minority carriers which is directly related to diffusion length. This article is concerned with the extension of this method to Photoluminescence (PL), allowing for a diffusion length mapping in all stages of cell production. Problems associated with this method - such as filter inhomogeneities, fluorescence of filters, texturing, the nature of surface reflection and surface recombination - are addressed. Different PL measurement setups are discussed theoretically and with respect to measurement results. Diffusion length images measured with the technique are demonstrated.