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Institute Nanospectroscopy

Spin-Dependent Transport in Fully Processed Silicon Solar Cells Studied by Pulsed Multifrequency Electrically Detected Magnetic Resonance below 600 MHz/20 mT and at 263 GHz/ 9.4 T

In both, thin-film silicon and wafer-based crystalline silicon (c-Si) solar cells, a 10 nm thin hydrogenated amorphous silicon (a-Si:H) layer acts as charge selective hetero contact. a-Si:H layers effectively passivate interface defects, still a small sub-ensemble of paramagnetic defects remain and influence the solar conversion efficiency. Since such heterointerfaces are also present in absorberlayers of microcrystalline silicon (μc-Si:H) their detailed understanding is a prerequisite for optimization strategies leading to a-Si/c-Si and TFS solar cells with higher efficiency. To access interface defects in state of the art silicon solar cells, the sensitivity limit of EPR has to be lifted and spectral resolution has to be improved. In the proposed work, we combine recent breakthroughs in the field of pulsed electrically detected magnetic resonance (pEDMR) with the availability of high-field EPR spectrometers to study spin-dependent transport processes by pEDMR at resonance conditions ranging from below 600 MHz/20 mT up to 263 GHz/9.4 T on the same solar cell. This approach will yield the following benefits. 1.) Separation of overlapping resonance signals and the extraction of structural information via g- and hyperfine tensors and their interpretation by density functional theory (DFT) calculations; 2.) Insight into spin-dependent transport and recombination processes by field and temperature induced switching between different transport and recombination regimes.