Microscopic Mechanism of the Staebler-Wronski Effect in a-Si Films and High-Efficiency Solar Cells: Final Subcontract Report, 1 October 2001--30 September 2004

In high growth rate (= 50 ..ANG../s) HW-CVD a-Si:H films, for the first time, we show gaseous molecules in nanovoids (~2% volume fraction of tube-like nanoscale voids), and demonstrate that confinement on the nanometer scale generates NMR effects that have never been observed in macroscopic systems. In the same system we found the PL peak red shift. We suggest that highly strained bonds on the innersurfaces of the nanoscale voids form broad conduction-band tail states that are responsible for the PL red shift. We characterized the structural transition from a- to nc-Si as function of H-dilution, thickness and Ts of both HW- and PE-CVD films using IR, Raman, PL, CPM/PDS and Ea et al. We found not only the c-Si volume fraction but also the g.b. and microstructures play an important role inthe properties of the i-layer and their solar cell performance. We found a narrow structural transition zone in which the bond-angle variation decreases from 10 deg to 8 deg. For nc-Si samples, we found a characteristic low energy PL peak and proved that is originated from the g.b. regions. Using micro-Raman, we found the structural non-uniformity in the mixed-phase solar cells that showed Vocenhancement after light soaking. Using micro-Raman, we also found the slight increase of crystallinity in M/..mu..c-Si/M devices after current forming.