Carrier-collection efficiencies in amorphous hydrogenated silicon Schottky-barrier solar cells

We report the results of a systematic study of correlations in the collection efficiency, collection length, depletion width, midgap density of states and energy-band gap in sputter and silane-decomposition-produced amorphous hydrogenated silicon Schottky diodes. Films produced by sputtering have a collection length Lc, which is less than the depletion width W, unlike silane-decomposition-produced films for which Lc≃W. We show that the relatively weak variation of the deduced hole-mobility-lifetime product with midgap state density and temperature is consistent with the holes becoming immobilized before recombining. The collection efficiency is found to be controlled dominantly by the field-assisted diffusion of carriers in the depletion region, and not limited by geminate recombination.