We present a comprehensive computer simulation of energy conversion process for p-i-n amorphous silicon solar cells. This has been carried out by analyzing the trap quasi-Fermi level, electric field, recombination rate, free carrier, traped charge carrier, and current density profiles for a variety of bias voltage. We also calculate photovoltaic performance as functions of ionized dopant concentration, device thickness, temperature, and intensity. We interpret these results in terms of the asymmetrical density of localized states in the mobility gap.