Surface Modification of LPCVD ZnO-Films for Silicon Thin Film Solar Cells

The influence of the surface morphology of the front contact layer on the properties of amorphous silicon based solar cells is presented. Based on a textured LPCVD substrate, which consists of pyramidal grains emerging out of the surface plane, the surface topology is modified by plasma etching. By varying the gas composition in the plasma at a fixed total flow, we were able to create surface morphologies whose features show deviations from the pyramidal shape, without significantly changing the surface roughness. For the plasma etched samples JSC decreases in comparison to the as-deposited ZnO. The decrease in current is not exclusively caused by a degraded red response but also due to a lowered quantum efficiency in the whole visible spectral range. This is attributed to a degraded light incoupling at the ZnO/ a-Si interface due to the altered pyramidal shape. It could be shown experimentally that the shape of the surface morphology is important for light incoupling as well as light trapping.