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 the three materials. Nano porous Ti02 is used successfully in a novel solar cell featuring an organic dye absorber. This product is now at the brink of commercialization, while electronic applica tions for C60 still appear to be in the exploration phase. At this stage it appears that some of the insight and many of the exper imental techniques used in the development of a Si:H may prove useful in the on going and yet very basic study of TiO2 and C60 thin films. This idea is the guideline to this book. Without being comprehensive on the part of amorphous silicon, it attempts to outline basic characterization schemes for the nano porous and fullerene materials, and to evaluate their potential for applications with respect to a reference, which is given by a Si:H.