Effect of the Nature of Cadmium Salts on the Effectiveness of CdS SILAR Deposition and Its Consequences on the Performance of Sensitized Solar Cells

Nanocrystalline titania films deposited on FTO transparent electrodes were sensitized by CdS nanoparticles synthesized in situ by the SILAR method. Three precursor solutions were employed for adsorption of Cd 2+ ions: nitrate, sulfate, and acetate. The CdS load and the size of CdS nanoparticles varied a lot from one precursor to the other. The highest load and the largest nanoparticles were obtained in the case of cadmium acetate, the smallest in the case of nitrate, while sulfate gave intermediate values. Ultraviolet photoelectron spectroscopy was employed to measure the ionization potential (and valence band potential) for pure titania and for sensitized titania in the three cases. The obtained values were 7.4 eV for pure titania and 6.7, 6.6, and 5.7 eV for CdS-sensitized titania made by using cadmium nitrate, sulfate, and acetate precursors, respectively. The corresponding band gap values ranged between 2.5 and 2.3 eV. The thus characterized photoanodes were employed to make Quantum Dot Sensitized Solar Cells and PhotoFuelCells. Acetate-derived photoanodes were more effective in the case of Quantum Dot Sensitized Solar Cells, while nitrate-derived precursors were more effective in the case of PhotoFuelCells. This reversed behavior is due to the fact that, in the first type of cells, what matters is mainly the extent of sensitization capacity, while in the case of PhoFuelCells, what matters most is the capacity of the combined semiconductor to oxidize the fuel.