Experimental Study of the Factors Governing the Staebler-Wronski Photodegradation Effect in a-Si:H Solar Cells: Annual Subcontract Report, 1 April 1995 - 30 June 1996

This report describes continuing experiments on electroluminescence (EL), field profile, and H-microstructure studies of a-Si:H-based solar cells and materials. By using EL spectroscopy, we observed that both the band-tail width and the defect energy distribution are narrowed by H-dilution. We demonstrated the existence of the 'fast' and 'slow' defects in the cell performance and identified theirenergy positions as a~0.9 eV and a~0.75 eV defect EL band. Our results also reinforced the notion that H-dilution eliminates the microstructure that causes the creation of 'slow' defects and hence stabilizes rapidly under light illumination. We demonstrated that the internal-electric field profile of a-Si:H p-i-n structures can be measured by the transient-null-current method. For the firsttime, hot-wire-deposited a-Si:H films were characterized by 1H nuclear magnetic resonance. Surprisingly, about 90 percent of the H atoms give rise to the 50-kHz line, and only a very small percentage of the H atoms give rise to the 3-kHz-narrower resonance line, which suggests that H-bonding in hot-wire films is very different from that in a-Si:H produced by plasma-enhanced chemical vapordeposition.