Electron trapping by excited microvoids (ETEM) -: an explanation of the Staebler-Wronski effect

The use of amorphous, hydrogenated silicon (a-Si:H) in photovoltaic devices is limited by a severe light-induced degradation which can be reversed by thermal annealing in the dark (Staebler-Wronski effect). Despite a lot of efforts in the past there is no generally accepted idea regarding the mechanism of this process. We present a new proposal relying on the concept of electron trapping by excited microvoids (ETEM). This concept avoids the weaknesses and failings of previous attempts and allows for a reasonable description of the kinetics of the process, yielding a limit value of the photoconductivity in nearly quantitative agreement with the experimental observation. Hydrogen diffusion is not necessary, and the findings of light-induced ESR spectroscopy (LESR) fit into our model quite naturally. Results of quantum-chemical calculations indicate that the essential species appearing in the sequence of reaction steps are actually present in a-Si:H. (C) 2004 Elsevier B.V. All rights reserved.