Evaporated polycrystalline silicon films for photovoltaic applications - grain size effects

Vacuum deposited, polycrystalline silicon films were fabricated into planar photovoltaic diodes by double diffusion techniques. Scanning electron microscopy showed that the crystallites are columnar in shape, with grain lengths several times larger than grain diameters. The dependency of average grain diameter on deposition conditions is discussed. Secondary ion mass spectrometry was used to obtain doping profiles and junction depths. Dark and illuminated I-V curves, spectral responses, and minority carrier diffusion lengths are presented for photovoltaic devices having grain sizes in the range 0.2 to 5 μm. Samples formed on sapphire and on a special alkaline-earth aluminosillcate glass processed under the same conditions had similar photovoltaic characteristics. Data on open-circuit voltage, short-circuit current, and solar cell efficiency are presented as functions of average grain diameter.