The major objectives of this subcontract have been (1) to understand the microscopic properties of the defects that contribute to the Staebler-Wronski effect in order to eliminate this effect, (2) to perform correlated studies on films and devices made by novel techniques, especially those with promise to improve stability or deposition rates, (3) to understand the structural, electronic and optical properties of films of hydrogenated amorphous silicon (a-Si:H) made on the boundary between the amorphous and microcrystalline phases, (4) to search for more stable intrinsic layers of a-Si:H, (5) to characterize the important defects, impurities, and metastabilities in the bulk and at surfaces and interfaces in a-Si:H films and devices and in important alloy systems, and (6) to make state-of-the-art plasma enhanced chemical vapor deposition (PECVD) devices out of new, advanced materials when appropriate. All of these goals are highly relevant to the improvement of photovoltaic (PV) devices based on a-Si:H and related alloys. With regard to the first objective, we have identified a paired hydrogen site that may be the defect that stabilizes the silicon dangling bonds formed in the Staebler-Wronski effect.
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