Optical simulation has been employed, for the first time, for rigorous evaluation of transmittance into the TiO2 nanocrystalline film, entering from the fluorine-doped SnO2 (F-SnO2) coated glass side, in dye sensitized solar cells. The refractive index of the TiO2 film with various porosities was determined theoretically, and was in agreement with the data obtained by ellipsometric measurements. The simulation clearly indicates that the transmittance into the TiO2 film is 85-90% at 450-800 nm, on adjusting the porosity to 0.5-0.75. In contrast, transmittances experimentally determined for the TiO2 film deposited on F-SnO2 exhibits 70-83% at 450-800nm, underestimating the transmittance by about 10% compared to the simulated results. The simulation method was further substantiated by observing the high IPCE value (similar to 85% at 530nm) for the solar cell using the same TiO2 film sensitized by ruthenium dye. (c) 2006 Elsevier B.V. All rights reserved.