Synergistic enhancement of charge transfer and catalytic activity in CNT@rGO@Cu2S composite counter electrodes for high-performance quantum dot-sensitized solar cells

Abstract

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@Cu₂S composite CE was synthesized using a hydrothermal method, incorporating carbon nanotubes (CNTs), reduced graphene oxide (rGO), and Cu₂S nanoparticles to enhance the charge transfer and catalytic activity. Structural characterization (XRD, Raman, FESEM, and HRTEM) confirmed the successful integration of the Cu₂S 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@Cu₂S composite, exhibiting the highest exchange current density (J₀) and lowest charge transfer resistance (R_ct1), indicating efficient polysulfide redox reactions. When employed in QDSSCs with a CdS/CdSe co-sensitized photoanode, the 6% CNT@rGO@Cu₂S CE achieved a power conversion efficiency (PCE) of 5.965%, surpassing those of rGO@Cu₂S (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.