In situ growth of CuS and Cu1.8S nanosheet arrays as efficient counter electrodes for quantum dot-sensitized solar cells

Abstract

Vertical CuS nanosheet arrays were synthesized in situ for the first time on transparent conducting fluorine-doped tin oxide (FTO) substrates via a facile solvothermal process of seeded FTO glasses in the presence of ethanol solvent only containing thiourea and Cu(NO₃)₂ as a precursor. While choosing CuCl instead of Cu(NO₃)₂ as the copper precursor in the same solvothermal process, porous Cu_1.8S nanosheets, for the first time, were also vertically grown on FTO substrates, suggesting that such a synthesis process is a general approach for the preparation of copper sulfide nanosheet arrays. When used as low-cost counter electrode materials in quantum dot-sensitized solar cells (QDSSCs), CuS (3.95%) and Cu_1.8S (3.30%) nanosheet films exhibited enhanced power conversion efficiencies in comparison with the conventional Pt film (1.99%), which was primarily due to the excellent electrocatalytic activity of copper sulfides for the reduction of the polysulfide electrolyte used in CdSe/CdS QDSSCs. Significantly, the in situ growth strategy largely simplified the fabrication procedure of copper sulfide counter electrodes and, meanwhile, enhanced the adhesion between films and substrates.