Analysis of charge transport kinetics in photovoltaic based on FTO@TiO2@CdS:Cu²⁺@ZnS photoanode

Abstract

This study examines charge-transport kinetics in TiO₂@CdS:Cu²⁺@ZnS quantum dot-sensitized solar cells, addressing a key research gap regarding how controlled Cu²⁺ incorporation simultaneously affects recombination dynamics and interfacial charge-transfer resistances. While previous works mainly emphasized optical improvements from Cu doping, the coupled effects on impedance characteristics and device performance remain insufficiently clarified. Cu-doped CdS quantum dots with concentrations ranging from 0 to 0.5 mol were synthesized via the SILAR method and protected with a ZnS passivation layer. Electrochemical impedance spectroscopy and I-V characterization were employed to quantify changes in Rct1, Rct2, Jsc, Voc, fill factor, and power conversion efficiency. The optimal Cu(0.2) device achieved 4.69% efficiency with a Jsc of 27.4 mA/cm², reflecting enhanced charge transport, reduced recombination, and improved light absorption. The findings reveal the previously underexplored dual role of Cu doping in tuning both optical and electronic properties. Furthermore, they identify the threshold at which excessive Cu leads to recombination-dominated losses and structural degradation. This work establishes a clearer mechanistic basis for engineering high-performance quantum absorber architectures in next-generation solar cell technologies.