Electron transfer between the electronically excited state of a dye and a semiconductor was discovered in 1887 by James Moser at the University of Vienna. He observed that the photoelectric effect detected on silver plates treated with iodide or bromide was greatly enhanced in the presence of erythrosine. A few years later, H. Vogel in Berlin exploited this phenomenon to render silver halide microcrystals sensitive to visible light, a process which eventually found wide application in color photography. Apart from the fundamental importance for photography and xerography, current investigations are fueled by the recent discovery of dye-sensitized injection solar cells. These cells have already reached an impressive conversion efficiency of 11% under full sunlight, rendering them competitive with commercial silicon-based devices.