Improved performance of CdSe quantum dot-sensitized TiO2 thin film by surface treatment with TiCl4

A TiO2 nanocrystalline thin film, sensitized by CdSe quantum dots, was further modified by a TiCl4 treatment strategy. The CdSe quantum dots with a cubic zinc blende structure were synthesized in situ on the TiO2 nanocrystalline thin films by chemical bath deposition, after which the sensitized TiO2 film was further modified by a TiCl4 treatment strategy. The modification of the amorphous TiO2 thin layer enhanced the photovoltaic performance of the quantum dot-sensitized thin film. This enhancement was detected by fabricating a solar cell based on the sensitized thin film electrode, a polysulfide electrolyte and a platinized electrode. The modified amorphous TiO2 was partly crystallized by heating the film at 200 °C to analyze the effect of crystallization on interfacial recombination and the photovoltaic performance. The enhancement due to the TiCl4 treatment was attributed to the formation of an amorphous TiO2 thin layer, which separated the uncovered surface of TiO2 nanoparticles from the electrolyte, and reduced the surface states of the TiO2 nanocrystals and the quantum dots. The highest conversion efficiency was 2.13%, and it was obtained for the quantum dot-sensitized solar cell after optimizing the CdSe quantum dot deposition and amorphous TiO2 thin layer modification processes.