Growth of CdS nanocrystals within mesoporous TiO2 films by using cadmium thiolates derivatives as unimolecular precursors

In this work we report on the synthesis and the characterization of CdS nanocrystals (NCs) in mesoporous TiO2 anatase films as a first step towards the production of quantum dot sensitized TiO2 based solar cells. A novel in-situ approach has been devised using a unimolecular precursor, containing both the metal and the non-metal part. A [Cd(SR)2]Ln cadmium thiolate complex, where L represents 1-methylimidazole, has been prepared in order to maximize the adsorption into the TiO2 pores. The thiolate complex absorbed in TiO2 can be decomposed at 500°C in argon atmosphere in order to obtain the final CdS/TiO2 composite material. The optical properties of the final product have been monitored by UV-Vis transmission spectroscopy carried out with non polarized light and at normal incidence with respect to the sample surface. The morphology and porosity of the TiO2 matrix have been investigated by scanning electron microscopy. X-ray diffraction and transmission electron microscopy have been performed in order to study the crystalline structure of the samples and to estimate the TiO2 and CdS NCs size. The proposed synthesis strategy allows us to fabricate tailored band gap CdS/TiO2 composite material, with 10 nm to 100 nm diameter for TiO2 anatase crystallite pores and 3.2 nm average diameter for CdS NCs.