Large-scale synthesis of Cu₂SnS₃ and Cu _1.8S hierarchical microspheres as efficient counter electrode materials for quantum dot sensitized solar cells

Exploration of new catalytic semiconductors with novel structures as counter electrode materials is a promising approach to improve performances of quantum dot sensitized solar cells (QDSSCs). In this work, nearly mono-disperse tetragonal Cu₂SnS₃ (CTS) and rhombohedral Cu _1.8S hierarchical microspheres with nanometer-to-micrometer dimensions have been synthesized respectively via a simple solvothermal approach. These microspheres are also demonstrated as efficient counter electrode materials in solar cells using ZnO/ZnSe/CdSe nanocables as photoanode and polysulfide (S_n^2-/S^2-) solution as electrolyte. While copper sulfide is regarded as one of the most effective counter electrode materials in QDSSCs, we demonstrate the CTS microspheres to show higher electrocatalytic activity for the reduction of polysulfide electrolyte than the Cu_1.8S microspheres. This contributes to obvious enhancement of photocurrent density (J_SC) and fill factor (FF). Power conversion efficiency (PCE) is significantly enhanced from 0.25% for the cell using a pure FTO (SnO₂:F) glass as counter electrode, to 3.65 and 4.06% for the cells using counter electrodes of FTO glasses coated respectively with Cu_1.8S and CTS microspheres. © 2012 The Royal Society of Chemistry.