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Highly porous nanocrystalline films of TiO 2 sensitized with semiconductor nanocrystals (NCs) are very promising for photovoltaic applications, NCs being more versatile and efficient than organic dyes as sensitizer. In this framework, the visible light absorption of TiO 2 can be improved by the superposition of CdS NC absorption band, that is tunable between 2.5 and 5.2 eV. Here, we report on a novel in situ approach for the synthesis of CdS NCs in mesoporous sol-gel TiO 2 anatase films by using as starting reagent for CdS, [Cd(SBz) 2 ]MI, where MI represents 1-methylimidazole. The precursor has been adsorbed into the TiO 2 pores and then decomposed at 480 °C, the procedure being studied for TiO 2 films with different porosity. The matrices have been investigated by atomic force microscopy. X-ray diffraction measurements on TiO 2 matrix and on the corresponding CdS/TiO 2 nanocomposite material revealed a variation of the NCs size of both TiO 2 and CdS as a function of the matrix porosity. The optical properties of the TiO 2 and CdS/TiO 2 have been studied by UV-Vis transmission spectroscopy. CdS/TiO 2 nanocomposites, having higher absorption efficiency with respect to TiO 2 , are suitable as building blocks for 3rd generation solar cell design.