Forty years of the Staebler-Wronski effect

This article describes highlights of investigations of the Staebler-Wronski effect (SWE), observed in hydrogenated amorphous silicon since its discovery. Some of the basic characteristics of SWE are discussed along with some solved and unsolved puzzles. Particular emphasis is given to a recent model based on long-range potential fluctuations caused by heterogeneities present in the films. Evidence is reviewed for the presence of several kinds of dangling-bond defects produced by light exposure (hv>1.3eV) at different temperatures between 4.2 and 360K. With exposure at lower temperature the defects become less stable, but they possess larger recombination cross-sections. Voids in the material have been identified as the location for light-induced defects most harmful to the efficiency of solar cells. Ways to eliminate them are discussed. We suggest that progress in this field was delayed by lack of sample sharing among laboratories.