Infrared modulation spectroscopy of interfaces in amorphous silicon solar cells

We report infrared depletion modulation spectra for near-interface states in a-Si pin solar cells. The effect of additional visible illumination (optical bias) was explored as a means to separate the spectra for n/i and p/i interface states. We found a sharp, optical bias-induced spectral line near 0.8 eV. We attribute this line due to internal optical transitions of dopant-defect complexes in the a-SiC:H:B p-layer of the cells. We discuss the spatial location of the depletion modulation regions, and suggest that this location shifts across the n/i and p/i interfaces for cells with differing deposition and illumination conditions.