Solid-phase crystallized Si films on glass substrates for thin film solar cells

We investigate the potential of solid-phase crystallized Si films on glass for use in polycrystalline Si thin film solar cells. Low-pressure chemical vapour deposition serves to form amorphous Si films on borosilicate, SiO2-coated borosilicate, aluminosilicate glass and fused silica substrates. The films are crystallized at temperatures of around 600 degrees C. Using transmission electron microscopy we determine the grain size in the crystallized films. The average grain size strongly depends on the substrate type, increases with the deposition rate of the amorphous film and is independent of the film thickness. The grain size distribution in our films is log-normal. Films crystallized on SiO2-coated borosilicate glass have an average grain size up to 2.3 mu m, while the area weighted average grain size peaks at 4 mu m. Since thin crystalline Si solar cells only require a film thickness of several micron, our films seem to be suitable for application to such devices.