Spin-Dependent Processes In Thin-Film Silicon Solar Cells

Abstract

ABSTRACTWe report on electrically detected magnetic resonance (EDMR) studies in three different types of thin-film silicon solar cells: (i) c-Si absorbers with epitaxially grown silicon thin-film emitters (ii) c-Si absorbers with hydrogenated amorphous silicon (a-Si:H) emitters, and (iii) microcrystalline silicon (µc-Si:H) pin diodes. Although cells of type (i) and (ii) are of a similar structure their EDMR spectra are completely different. We identify surface recombination via Pb0 centers in cells with c-Si emitters but hopping transport through conduction bandtail states in the 30 nm thin a-Si:H emitter layer. No signals related to interface recombination are detected in either cell. The EDMR signals of cell (iii) are identified as hopping among tail states of the conduction band with a subsequent nonradiative tunneling transition to neutral dangling bonds. At elevated temperature recombination is suggested to be dominated by direct capture. The EDMR signal of the dark current can be described with a simple diode model only involving diffusion and recombination currents.