Development of Nonstoichiometric CuInS₂ as a Light-Harvesting Photoanode and Catalytic Photocathode in a Sensitized Solar Cell

Abstract

A simple one-pot approach was developed to obtain nonstoichiometric CuInS₂ nanocrystals. Using this approach, both In-rich and Cu-rich CuInS₂ nanocrystals could be reliably synthesized by tuning stoichiometric combinations of [Cu]/[In] precursor constituents. By designing Cu-rich CuInS₂ heteronanostructures to serve as counter electrodes, quantum-dot-sensitized solar cells (QDSSCs) equipped with In-rich CuInS₂ and CdS cosensitizers delivered a power conversion efficiency of 2.37%, which is significantly more efficient than conventional Pt counter electrodes. To the best of our knowledge, this study represents the first report utilizing nonstoichiometric CuInS₂ nanocrystals as a photon-harvesting sensitizer comprised of a photoanode and photocathode in QDSSCs; also unique to this report, these nonstoichiometric CuInS₂ nanocrystals were formed by simply changing the cationic molar ratios without complicated precursor preparation. Impedance spectroscopy and Tafel polarization indicated that these Cu-rich CuInS₂ heteronanostructures had electrocatalytic activities (used for reducing S^2–/S_<i>n</i>^2–) that were superior to a Pt catalyst. Moreover, we demonstrated that Cu-rich CuInS₂ heteronanostructures were also useful counter electrodes in dye-sensitized solar cells, and this finding revealed a promising conversion efficiency of 6.11%, which was ∼96% of the efficiency in a cell with a Pt-based counter electrode (6.32%)