The highest efficiency of dye-sensitized solar cells (RuDSC) has been achieved with a Ru complex dye and nano-porous TiO₂. In order to increase the efficiency, novel dyes and matched semiconductors are desired. To date, some dyes have shown comparable short-circuit current with RuDSC, but none of them showed comparable open-circuit voltage (Voc). The lower Voc was attributed to shorter electron lifetime in these DSCs. Besides TiO₂, various semiconductors such as SnO₂, ZnO, and In₂O₃, have been examined, but TiO₂ have been the best. The lower efficiency of some semiconductors has been interpreted with higher electron mobility in the semiconductors, resulting in the faster interfacial recombination. In order to design DSC, it is important to understand the mechanism of the electron transfer processes, especially the transfer from the semiconductor to dye cation and/or I₃^-. The transfer rate is governed by transfer rate in the semiconductors, that is, transport limited, and interfacial transfer rate. To understand the mechanism, the effect of these should be ruled out, and then factors influencing each should be studied. For the purpose, we examined the electron diffusion and lifetime in DSCs prepared with semiconductors having different conduction band edge potentials and electron mobility, and with various dyes including both metal and metal-free dyes. It was found that the effective diffusion coefficients in SnO₂ and In₂O₃ were comparable and higher with that of TiO₂, respectively, and free energy difference has influences on the interfacial charge transfer rate. The degree of the influence of transport rate is discussed.