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

Abstract

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.