Large, rapid light induced changes are reported for photoconductivities, electron mobility‐lifetime products, and forward bias currents in hydrogenated amorphous silicon (a‐Si:H) films and Schottky barrier cell structures. The absence of concurrent changes in subgap absorption and quantum efficiencies are clearly inconsistent with the widely held view that the kinetics of degradation ina‐Si:H materials and cells can be quantified solely in terms of neutral dangling bond defects. The self‐consistent analysis of all the results was carried out for films and Schottky barrier structures by including charged defects and using a three‐Gaussian distribution of donorlike and acceptorlike defect states. Such self‐consistent development of ‘‘operational’’ parameters for these gap states offers a method for reliable and quantitative correlations between solar cell performance and stability with the properties of their bulk materials. ©1996 American Institute of Physics.