Polyisothianaphthene/graphene nanocomposite as a new counter electrode material for high performance dye sensitized solar cell

We report that a new nanocomposite viz. polyisothianaphene (PITN)/graphene can function as a highly efficient counter electrode (CE), replacing the conventionally used Pt CE in a dye sensitized solar cell (DSSC). The nanocomposite was prepared with varying polymer to graphene ratio in aqueous medium using poly(styrene sulfonate) as dispersing agent and characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy techniques. Cyclic voltammetry studies revealed that the nanocomposite prepared with 1:4 ratio of polymer to graphene (PITN/graphene (1:4)) showed a higher electrocatalytic activity than Pt for the reduction of triiodide ions. Electrochemical impedance spectroscopy and Tafel analysis data for the symmetrical cells indicated a lower charge transfer resistance and higher exchange current density for PITN/graphene (1:4) than Pt. The DSSC assembled with a N719 dye sensitized TiO₂ (P25) photoanode, iodide/triiodide redox electrolyte and PITN/graphene (1:4) CE showed a photovoltaic power conversion efficiency of 5.2% which was found to be higher than that of the DSSCs made with pristine PITN (3.5%), graphene (2.5%) and sputtered Pt (4.5%) as CEs.