Synthesis of CdS/TiO2 nanocomposites by using cadmium thiolate derivatives as unimolecular precursors

Highly porous nanocrystalline films of TiO2 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 TiO2 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 TiO2 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 TiO2 pores and then decomposed at 480 8C, the procedure being studied for TiO2 films with different porosity. The matrices have been investigated by atomic force microscopy. X-ray diffraction measurements on TiO2 matrix and on the corresponding CdS/TiO2 nanocomposite material revealed a variation of the NCs size of both TiO2 and CdS as a function of the matrix porosity. The optical properties of the TiO2 and CdS/TiO2 have been studied by UV–Vis transmission spectroscopy. CdS/TiO2 nanocomposites, having higher absorption efficiency with respect to TiO2, are suitable as building blocks for 3rd generation solar cell design.