Increasing the light harvesting efficiency (LHE) of photovoltaic devices is important for improving the conversion efficiency of solar light into electricity. The optical properties of mesoporous TiO2 films for Dye-Sensitized Solar Cells (DSCs) were investigated by varying the size of the particles (20 - 150 nm). A four-flux optical model was used to describe the light absorption and scattering within the film. Reflectance and transmittance spectra were recorded by a spectrophotometer equipped with an integrating sphere. The wavelength-dependent absorption coefficient k(λ) and scattering coefficient s(λ) were determined for different films. The absorptance G(λ) (absorbed light flux) for films made of different particle sizes and of varying thicknesses can be calculated from these optical parameters. This study helps in improving the optical design of dye-sensitized solar cells.