The factors that limit photocurrent in dye solar cells (DSC) were studied by incident-photon-to-collected-electron efficiency (ηIPCE), optical, and photovoltaic measurements. Nanostructured TiO2 photoelectrodes were prepared by compression technique on glass substrates, and half of them were given an additional heat treatment at 450 °C. The spectral absorbed-photon-to-collected-electron efficiency (ηAPCE) of the cells was determined as a function of the photoelectrode film thickness (d) and direction of illumination and analyzed in terms of electron injection (ηINJ) and collection (ηCOL) efficiency. The cells with pressed-only photoelectrodes gave significantly lower photocurrents yet their ηAPCE, and thus ηCOL, increased significantly with increasing d. To analyze this result quantitatively, methods were formulated based on the standard diffusion model of electron transport in nanostructured photoelectrodes for the factorization of experimental ηAPCE data into ηINJ and ηCOL parts and subsequent estimatio...