Pt/CuSe: a new counter electrode for polyiodide reduction in quantum dot-sensitized solar cells

The most common structure of a quantum dot-sensitized solar cell (QDSC) employs a metal sulfide counter electrode (CE) combined with a polysulfide electrolyte (S2-/S-n(2-)). Polyiodide electrolytes (I-/I-3(-)) have an advantage over polysulfide because of their high photovoltage output. However, most semiconductor QDs will dissolve in polyiodide. This work presents a new double-layer CE material Pt/CuSe that is compatible with polyiodide. The electrocatalytic activity of three types of CEs: Pt, CuSe and Pt/CuSe, are compared using cyclic voltammetry, Tafel plots and electrochemical impedance spectroscopy. Among the three CEs, the Pt/CuSe CE exhibits the best catalytic activity with low charge transfer resistance and a high current density. Pt/CuSe CEs are then applied in ternary Pb(5)Sb(8)S(17)QDSCs that are stable in polyiodide. The QDSC with the Pt/CuSe CE exhibits a power conversion efficiency (PCE) of 3.71% (with ZnS passivation), which is significantly higher than those of cells with Pt (2.53%) and CuSe (2.68%) CEs. At the reduced intensity of 0.1 sun, the PCE further increases to 5.54%, a respectable efficiency for a QDSC. To the best of our knowledge, Pt/CuSe is the first CE for QDSCs using polyiodide and has the potential for improving performance in QDSCs.