This volume discusses the photoelectric behavior of three semiconducting thin film materials hydrogenated amorphous silicon (a Si: H), nano porous titanium dioxide, and the fullerene C60. Despite the fundamental structural differences between these materials, their electronic properties are at least on the phenomenological level surprisingly similar, since all three materials have rather low carrier mobilities. In the last decade a Si: H has conquered large market segments in photo voltaics, fiat panel displays and detector applications. It is surely the most advanced and best understood of...