Electronic Processes in Thin-Film PV Materials: Final Report

The electronic and optical processes in an important class of thin-film PV materials, hydrogenated amorphous silicon (a-Si:H) and related alloys, have been investigated using several experimental techniques designed for thin-film geometries. The experimental techniques include various magnetic resonance and optical spectroscopies and combinations of these two spectroscopies. Two-step opticalexcitation processes through the manifold of silicon dangling bond states have been identified as important at low-excitation energies. Local hydrogen motion has been studied using nuclear magnetic resonance (NMR) techniques and found to be more rapid than long-range diffusion as measured by secondary-ion mass spectroscopy. A new metastable effect has been found in a-Si:H films alloyed withsulfur. Spin-one optically excited states have been unambiguously identified using optically detected electron spin resonance. Local hydrogen bonding in microcrystalline silicon films has been studied using NMR.