Epitaxial Crystal Silicon Absorber Layers and Solar Cells Grown at 1.8 Microns per Minute

We have grown device-quality epitaxial silicon thin films at growth rates up to 1.85 μm/min, using hot-wire chemical vapor deposition from silane, at substrate temperatures below 750°C. At these rates, which are more than 30 times faster than those used by the amorphous and nanocrystalline Si industry, capital costs for large-scale solar cell production would be dramatically reduced, even for cell absorber layers up to 10 μm thick. We achieved high growth rates by optimizing the three key parameters: silane flow, depletion, and filament geometry, based on our model developed earlier. Hydrogen coverage of the filament surface likely limits silane decomposition and growth rate at high system pressures. No considerable deterioration in PV device performance is observed when grown at high rate, provided that the epitaxial growth is initiated at low rate. A simple mesa device structure (wafer/epi Si/a-Si(i)/a-Si:H(p)/ITO) with a 2.3 μm thick epitaxial silicon absorber layer was grown at 0.7 μm/min. The finished device had an open-circuit voltage of 0.424 V without hydrogenation treatment.