This paper addresses the influence of the glass/TCO-substrates on the performance of p-i-n thin film silicon solar cells. We investigate various commercially available glass/SnO2-substrates as well as magnetron-sputtered and chemically textured ZnO prepared in-house. In detail, we study differences in type and thickness of the glass substrate, the influence of material and light scattering properties of the TCO as well as measurement aspects when assessing and separating the individual effects.