Two-dimensional resolution of minority carrier diffusion constants in different silicon materials

Hall measurements are a common method to determine the majority charge carrier diffusion constant. But the diffusion constant of the minority carriers Dn, the more interesting parameter in photovoltaics, is rather hard to detect. In this paper we introduce a method to determine Dn locally resolved and mapped in two dimensions. For that purpose the local diffusion length Ldiff, which can be calculated from LBIC (laser beam induced current) measurements, has been combined with the local bulk lifetime τb received by μ-PCD (microwave-detected photo conductance decay) measurements. We evaluated the diffusion constants of the minority charge carriers Dn for different p-type silicon materials with a resolution of 100 μm. The measurements were carried out on solar cells before and after remote plasma hydrogen passivation in order to get an impression of the diffusion constant dependency on hydrogen incorporation.