Improvement of n-Type Poly-Si Film Properties by Solid Phase Crystallization Method

Polycrystalline silicon (poly-Si) thin films prepared by the solid phase crystallization (SPC) method were investigated for application as photovoltaic materials. To improve the properties of the poly-Si thin film, two methods were developed to control crystallization. One is the partial doping method, in which starting material of a-Si consists of a doped layer and an undoped layer. We have succeeded in controlling nuclei generation using partial doping, and high mobility of 196 cm 2 /V·s was obtained at a carrier concentration of 1×10 18 cm -3 . SPC temperature can also be decreased to 500°C. The other is adoption, for the first time, of a textured substrate which exerted effects on the enlargement of grain size in poly-Si thin films prepared by the SPC method. By combining the partial doping method with the textured substrate, an n-type poly-Si thin-film with the grain size of 6 µm was fabricated which showed the Hall mobility of 623 cm 2 /V·s (n: 3.0\times10 15 cm -3 ). In a solar cell (thickness: 12 µm) applying this film, a conversion efficiency of 6.2% was obtained and a collection efficiency of 50% was achieved at a wavelength of 900 nm.