CoNi2S4-reduced graphene oxide nanohybrid: An excellent counter electrode for Pt-free DSSC

Dye sensitized solar cell (DSSC) technology could become a low-cost solution for solar energy harvesting if the use of expensive dyes and Pt can be avoided. This work reports the development of a novel nanohybrid based on CoNi2S4 nanorods embedded on sheets of reduced graphene oxide (RGO), which can serve as excellent counter electrode for DSSC showing great promise to replace Pt. The structural and morphological characterisation of the nanocomposite synthesised using a simple one step hydrothermal method revealed well defined crystalline nanorods of CoNi2S4 (with length 195 nm and diameter 8.34 nm) uniformly embedded on the surfaces of the RGO sheets (similar to 2.55 mu m in size). The morphology and size of the nanorods were found to be dependent on the duration of the hydrothermal reaction. The optimized CoNi2S4/RGO nanohybrid film when used as counter electrode in DSSC, photo conversion efficiency as high as 9.22% was recorded, a value almost equal to that obtained from the DSSC fabricated with Pt as counter electrode and much higher than that with bare CoNi2S4 justifying its potential use in Pt-free DSSC. The improved performance of the electrode have been attributed to the hierarchical nanohybrid structure consisting of catalytically active 1D CoNi2S4 nanorods embedded on electrically conducting 2D RGO sheets that provides fast ion diffusion pathways, large accessible surface area and good chemical and thermal stability.