2D/2D-Graphene Functionalized MXene as an Alternative Counter Electrode for Dye-Sensitized Solar Cells

This study investigates a prospective alternative to counter electrodes (CEs) composed of noble metals for dye-sensitized solar cells (DSSCs). By adopting a simplistic acid-etching method and direct blending of MXene and Graphene, we fabricated a novel 2D-2D MXene-graphene (MX-GE CE) counter electrode (MX-GE CE). The formation of a 2D-2D MX-GE structure was confirmed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. In addition, X-ray photoelectron spectroscopy (XPS) disclosed the interaction between MX and GE, resulting in a structure with pronounced electrocatalytic active sites that enabled outstanding catalytic performance with respect to the iodide/triiodide electrolyte. To determine the optimal weight ratio for device fabrication and to evaluate the stability of MX-GE, various distinct weight ratios of MX-GE were used. Using DFT, the computational band structure, electron density profile, and eigenstate values were analyzed. The results showed that the MX-GE composite with a 2:1 weight ratio had high eigenstate profiles and a larger energy spacing between electronic states, making it suitable as a Pt-free counter electrode in DSSCs. The MX-GE CE exhibited minimal resistance for charge transfer, accelerated kinetics of charge transfer, and efficient diffusion of electrons. The DSSC built using a photoanode loaded with N719 dye and MX-GE CE attained a notable power conversion efficiency (PCE) of 6.4%. Significantly, this PCE was comparable to a DSSC constructed with a conventional Pt CE (8%) under identical testing conditions. These results imply that the synthesized material as a counter electrode has considerable potential as a Pt substitute for DSSC counter electrodes.