Synergistic enhancement of charge transfer and catalytic activity in CNT@rGO@CuS composite counter electrodes for high-performance quantum dot-sensitized solar cells.

Developing cost-effective high-performance counter electrodes (CEs) is critical for improving the efficiency of quantum dot-sensitized solar cells (QDSSCs). In this study, a CNT@rGO@CuS composite CE was synthesized using a hydrothermal method, incorporating carbon nanotubes (CNTs), reduced graphene oxide (rGO), and CuS nanoparticles to enhance the charge transfer and catalytic activity. Structural characterization (XRD, Raman, FESEM, and HRTEM) confirmed the successful integration of the CuS nanoflowers within the rGO matrix. CNTs formed a conductive network that prevented rGO restacking and facilitated electron transport. Electrochemical analysis (CV, EIS, and Tafel polarization) demonstrated the superior electrocatalytic activity of the 6% CNT@rGO@CuS composite, exhibiting the highest exchange current density ( ) and lowest charge transfer resistance ( ), indicating efficient polysulfide redox reactions. When employed in QDSSCs with a CdS/CdSe co-sensitized photoanode, the 6% CNT@rGO@CuS CE achieved a power conversion efficiency (PCE) of 5.965%, surpassing those of rGO@CuS (5.322%) and conventional Pt-based CEs (1.96%). The superior performance is attributed to the optimized Fermi level alignment with the redox couple, enhanced charge mobility due to the CNTs, and improved electrolyte penetration.