Choice of materials for photovoltaic solar cells is discussed, taking into account two factors, viz. conversion efficiency and production COSIS. Thereby, physical considerations (band gap) and general factors (materia! availability and toxicity) are developed. Deposition of hydrogenated amorphous silicon (d-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 "VI-IF plasma deposition prccess introduced by the authors' laboratory is given special consideration.