Enhanced Quantum Dot Sensitized Solar Cells Performance with One-Step Synthesized Co0.85Se Counter Electrode

: The counter electrode (CE) with high catalytic activity has been vital to improve photovoltaic performance of quantum dot sensitized solar cells (QDSSCs). Cobalt selenide has been proved to have outstanding electrocatalytic activity among the electrode materials. In this work, Co0.85Se films were directly deposited on the F doped SnO₂ glass (FTO) substrate by one-step solvothermal method. The film phase and microstructure were characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM), respectively. Further, the effects of starting reactant concentration on the uniformity and continuity of Co0.85Se films were determined by scanning electron microscope (SEM) and energy-dispersive spectrometer (EDS). Then, QDSSCs with Co0.85Se film as CE and CdS/CdSe/TiO₂ film as photoanode obtained a power conversion efficiency of 2.4%, which exceeded reported efficiency by 14%. Electrochemical impedance spectra (EIS) and Tafel-polarization measurements indicated that the enhanced performance was attributed to the superior catalytic activity and high diffusion coefficient at the interface between Co0.85Se CE and polysulfide electrolyte.