Photovoltaic Properties of CdSe Quantum Dot Sensitized Inverse Opal TiO₂ Solar Cells: The Effect of TiCl₄ Post Treatment

Abstract

Recently, semiconductor quantum dot (QD) sensitized solar cells (QDSSCs) are expected to achieve higher conversion efficiency because of the large light absorption coefficient and multiple exciton generation in QDs. The morphology of TiO 2 electrode is one of the most important factors in QDSSCs. Inverse opal (IO) TiO 2 electrode, which has periodic mesoporous structure, is useful for QDSSCs because of better penetration of electrolyte than conventional nanoparticulate TiO 2 electrode. In addition, the ordered three dimensional structure of IO-TiO 2 would be better for electron transport. We have found that open circuit voltage Voc of QDSSCs with IO-TiO 2 electrodes was much higher (0.2 V) than that with nanoparticulate TiO 2 electrodes. But short circuit current density Jsc was lower in the case of IO-TiO2 electrodes because of the smaller surface area of IO-TiO 2 . In this study, for increasing surface area of IO-TiO 2 , we applied TiCl 4 post treatment on IO-TiO 2 and investigated the effect of the post treatment on photovoltaic properties of CdSe QD sensitized IO-TiO 2 solar cells. It was found that J sc could be enhanced due to TiCl 4 post treatment, but decreased again for more than one cycle treatment, which indicates excess post treatment may lead to worse penetration of electrolyte. Our results indicate that the appropriate post treatment can improve the energy conversion efficiency of the QDSSCs.