We performed a detailed and quantitative spectroscopic study of the electron injection dynamics for porphyrin as one of organic dyes at an adequate level to discuss the dye-sensitized solar cell performance. The electron injection kinetics and the electron injection yield for dye-sensitized TiO 2 electrodes in redox-containing electrolytes were measured by femtosecond transient absorption and picosecond fluorescence spectroscopy. By comparing the dynamics of two of the most studied porphyrins with those of a Ru complex (N719), we have directly elucidated that the short-circuit current for the porphyrin-sensitized solar cells is limited by the presence of excited dyes that are quenched in the subnanosecond time range without competing with the electron injection process, even though both porphyrins shows faster injection processes within the picosecond time range than N719. Therefore, it was clearly indicated the electron injection efficiency was mainly limited by the inhomogeniety, which should be carefully considered for further development of organic dye-sensitized solar cells. © 2011 American Chemical Society.