Sodium Molybdate-Assisted Synthesis of a Cobalt Phosphide Hybrid Counter Electrode for Highly Efficient Dye-Sensitized Solar Cells

Designing efficient and economical dye-sensitized solar cells (DSSCs) free of precious metals is required to replace the platinum counter electrode (Pt CE) for further large-scale development. Herein, we have designed a sodium molybdate-assisted strategy for growing a transition-metal phosphide composite of cobalt phosphide and cobalt molybdenum phosphorus (CoP/CoMoP2) on carbon paper via the hydrothermal reaction and low-temperature phosphating methods. The CoP/CoMoP2 composite with a spherical polyhedral structure has been shown to exhibit better electrochemical and photoelectrochemical properties than the Pt and pure CoP CEs through a series of electrochemical and photoelectrochemical tests. Interestingly, the short-current density of the DSSC with the CoP/CoMoP2 CE has been greatly improved after adding sodium molybdate than that of the DSSC with the CoP CE. Under optimal conditions, the DSSC based on the CoP/CoMoP2 composite CE achieves impressive power conversion efficiency as high as 8.69%, which remarkably exceeds that of the DSSCs with the CoP CE (6.19%) and the Pt CE (7.74%).