Efficient dye-sensitized solar cells with CoSe/graphene composite counter electrodes

CoSe/graphene nanocomposites with various graphene content were synthesized via a simple low-temperature hydrothermal method and used as counter electrode (CE) in dye sensitized solar cells (DSSC). SEM shows that CoSe0.85 particles are self-assembled to a potato-chip-like morphology and loaded on graphene sheets. Cyclic voltammetry and electrochemical impedance spectroscopy and Tafel polarization analyses revealed that the CoSe0.85/graphene composite CE with the weight ratio of graphene of 75% exhibited higher electrocatalytic activity for the reduction of triiodide to iodide and lower charge transfer resistance at the CE/electrolyte interface than the other compositions. The DSSC with the optimized CoSe0.85/graphene as composite CE produces a maximum power conversion efficiency of 8.17%, which is better than bare CoSe0.85 CE.