Choice of materials for photovoltaic solar cells is discussed, taking into account two factors, viz, conversion efficiency and production costs. Thereby, physical considerations (band gap) and general factors (material availability and toxicity) are developed. Deposition of hydrogenated amorphous silicon (a-Si:H) for solar cells, in a silane glow discharge plasma is discussed in more detail; possibilities (e.g. amorphous alloys, tandem cells) and limitations (e.g. light induced-degradation) are mentioned. The novel 'VHF' plasma deposition process introduced by the authors' laboratory is given special consideration.