On the behavior of p-n junction solar cells made in fine-grained silicon layers

The behavior of polycrystalline p-n-junction solar cells with a grain size in the order of 1 mu m is investigated. The diffusion length appears larger than the average grain size at low doping levels but drastically decreases with increasing doping level, with moderate improvement through hydrogenation. The second diode currents are generally very large, leading to poor open-circuit voltages. We suggest that the zone of enhanced recombination, usually confined to the junction depletion region, extends into the base where very small grains are completely depleted due to carrier trapping at grain boundaries.