Light-induced degradation in undoped hydrogenated amorphous silicon films studied by the surface photovoltage technique: A comparison of lifetime versus space-charge effects

The calculation of the space-charge density under illumination from surface photovoltage measurements has been adapted to analyze light-soaking experiments in intrinsic hydrogenated amorphous silicon (a-Si:H). We find that the positive space-charge densities increase and the space-charge widths decrease with light exposure while very little change occurs in the hole diffusion length. These results indicate that changes in electric field distribution with light soaking are important causes of degradation of amorphous silicon solar cells, rather than changes which may ocur in the hole diffusion length. We also review and discuss results of others regarding application of the surface photovoltage (SPV) to study light-induced phenomena, evidence of two different types of light-induced defects, and potential limitations of SPV in a-Si:H.