2D-Ti3C2 MXenes decorated with WO3 as counter electrode catalysts for iodide redox shuttle in dye-sensitized solar cells

The modification and composite formation of MXenes by doping with transition metal compounds as counter electrode (CE) catalysts is an effective strategy for improving the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs). Herein, Ti3C2@WO3 composites were prepared by the hydrothermal method using two-dimensional titanium carbide MXenes (2D-Ti3C2) doped with tungsten trioxide (WO3) at mass ratios of 3:1, 2:1, 1:1, and 1:2. The effects of WO3 on the electrocatalytic activity of the Ti3C2@WO3 as CE catalysts are evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Tafel polarization. And then, DSSCs with the four different Ti3C2@WO3 catalysts yield PCEs of 6.75 % (3:1), 7.89 % (2:1), 7.56 % (1:1) and 6.40 % (1:2) for the regeneration of I3−/I− shuttles by the photocurrent-photovoltage tests, respectively. The excellent performance of Ti3C2@WO3 can be ascribed to the ordered interlayer structure of 2D-Ti3C2 MXene and the doping of WO3 results in the generation of a larger number of active sites due to changes in the microelectronic and geometric structures. Meanwhile, the two-phase interface between 2D-Ti3C2 and WO3 exist the built-in electric field to accelerate the diffusion of I3−/I− shuttle. Thus, Ti3C2@WO3 composites are expected to become the ideal Pt-free CE catalysts in the assembled DSSCs.