Flower-like nickel cobalt sulfide microspheres modified with nickel sulfide as Pt-free counter electrode for dye-sensitized solar cells

•The NiCo2S4/NiS microspheres are synthesized by a two-step hydrothermal method.•The NiCo2S4/NiS shows flower-like morphology and has a large specific surface area.•NiCo2S4/NiS CE exhibits excellent electrocatalytic activity and conductivity.•The DSSC with NiCo2S4/NiS CE obtains a PCE of 8.80% than that of DSSC with Pt CE.

The nickel cobalt sulfide/nickel sulfide (NiCo2S4/NiS) microspheres which exhibit flower-like morphologies are synthesized by a two-step hydrothermal method. Then the NiCo2S4/NiS microspheres are deposited on a fluorine doped SnO2 substrate by spin-casting the isopropyl alcohol solution of as-prepared microspheres. The cyclic voltammetry, electrochemical impedance spectroscopy and Tafel tests are employed to measure the electrochemical performance of NiCo2S4/NiS counter electrode. The NiCo2S4 and NiS all are used to improve the conductivity and electrocatalytic ability of the films, and the NiS can also increase the specific surface area of microspheres. The dye-sensitized solar cells (DSSCs) with the NiCo2S4/NiS counter electrode exhibite a power conversion efficiency of 8.8%, which is higher than that of DSSC with Pt counter electrode (8.1%) under the light intensity of 100 mW cm−2 (AM 1.5 G).

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