Diffusion length determination in thin-film Cu<i>x</i>S/CdS solar cells by scanning electron microscopy

Abstract

Minority-carrier diffusion lengths on both sides of the CuxS/CdS heterojunction in polycrystalline thin-film solar cells were determined from the decay of the short-circuit current generated by a 20-keV electron beam traversing the junction. The measured diffusion lengths in the low-field regions of these cells ranged from 0.11 to 0.57 μm for electrons in the p-type cuprous sulfide and from 0.07 to 0.31 μm for holes in the n-type cadmium sulfide. Uncertainties introduced by surface recombination effects, internal fields, and experimental accuracy specified that the actual bulk diffusion lengths could range from 0.09 to 1.71 μm for minority electrons in the cuprous sulfide and from 0.06 to 0.44 μm for minority holes in the cadmium sulfide. Measurement and analysis errors were estimated to cause bulk diffusion lengths to differ from measured values by less than the worst case limits of +200 and −31%.