The surface of the applied Al2O3 ceramic substrate consists of small crystals with a maximum grain size of 5 mum. A 40 mum thick layer deposited on this surface shows polycrystalline quality and grain sizes in the order of 10 mum. Silicon layers of different thickness and doping have been deposited on Al2O3 substrates to make thin film silicon solar cells. These structures have been processed to solar cells in a two mask process. From measurements of the spectral response a diffusion length of 8 mum can be extracted.