Petal-like cobalt selenide nanosheets used as counter electrode in high efficient dye-sensitized solar cells

A petal-like cobalt selenide nanosheets (Co0.85Se) is prepared by hydrothermal method and used as an efficient Pt-free counter electrode (CE) for dye-sensitized solar cells (DSSCs). Field emission scanning electron microscopy observes that the petal-like Co0.85Se possess porous and large specific surface area, which benefits the enhancement of electrocatalytic activity. Cyclic voltammogram measurement indicates that Co0.85Se electrode has larger current density than Pt electrode. Electrochemical impedance spectroscopy shows that the Co0.85Se electrode with optimal condition has low charge-transfer resistance of 0.79 Ω cm2. Under simulated solar light irradiation with intensity of 100 mW cm−2 (AM 1.5), the DSSC based on the Co0.85Se CE achieves a power conversion efficiency of 8.00 %, which is slightly higher than the solar cell based on the Pt CE (7.83 %).