Dependence of photoinduced changes in photovoltaic and dark electrical properties of hydrogenated amorphous silicon diodes on changes in the film properties of hydrogenated amorphous silicon

Computer simulation of hydrogenated amorphous silicon (a-Si:H) p-i-n type or n-i-p type diodes has been used to clarify the relationship between the photoinduced changes in photovoltaic and dark electrical properties of a-Si:H diodes and those in a-Si:H film properties. The origins of observed decrease in the short-circuit current and the fill factor are discussed referring to the decrease in carrier lifetimes, the change in electric field distribution in the undoped layer reflecting the increase in the density of ionized gap states, and the increase in interface recombination velcoity. Possible reasons for the observed differences in the photoinduced changes in photovoltaic properties between p-i-n type and n-i-p type a-Si:H diodes are also discussed. The observed changes in dark current-voltage characteristics of a-Si:H diodes can originate from the decrease in carrier lifetime. Some comments are also made on the "bulk or surface problem" of the photo-induced changes in a-Si:H p-i-n or n-i-p diodes.