Dye sensitized solar cells (DSC) prepared with Ru complex dye have shown over 11% energy conversion efficiency. While the efficiency of RuDSC has not improved largely for last decade, the efficiency of DSC prepared with metal-free organic dyes has been improved. Recent organic dyes have shown comparable short-circuit current with that of RuDSC. However, all of them have shown lower values of open-circuit voltage. We have measured the electron lifetime in DSCs with five different organic dyes, two coumarin dyes, and three carbazole dyes, and found that all of them had shorter electron lifetime than in the case of Ru dye. Among the organic dyes, the values of lifetime varied depending on the structure of the dyes. Two tendencies were found: dyes having larger molecular size and alkyl chains showed longer electron lifetime. In order to study the molecular structure dependent electron lifetime, electron diffusion coefficients, electron density, and transient absorption of the DSCs with these dyes were measured under various electrolyte compositions and amount of dye adsorptions. It was found that electron lifetime was increased with the increase of LiI concentrations and leveled off at certain concentrations, and the concentrations depend on the dyes. This suggests that some organic dyes needed more I^- concentrations to be reduced effectively. In view of amount of dye adsorption, dyes having alky chain showed longer lifetime when the amount of adsorbed dye is large, showing that these dyes block the approach of I₃^- to the surface of TiO₂.