Enhancing Absorption of Photon Using ZnSe Doped Copper as a Passivation Layer for Quantum Dot Solar Cell

In this study, the surface passivation of ZnSe quantum dots is compared with ZnSe quantum dots doped with copper metal at concentrations from 0.2 to 0.7% using chemical methods. They are coated on the TiO₂/CdS/CdSe@Cu²⁺ film to prevent the quantum dots to contact with the polysulfide electrolyte and increase the absorption of photons. The TiO₂/CdS/CdSe@Cu²⁺/ZnSe:Cu²⁺ photoanode were characterized by FESEM, structural studies by EDX mapping and X-ray diffraction, and optical properties by UV–Vis spectroscopy. As a result of the conversion efficiency, all samples with doping concentrations from 0 to 0.7% have a J-V characteristic curve. The highest efficiency corresponding to Cu²⁺– 0.3% doping concentration is 5.29%. Besides, we use semi-empirical formulas to study the absorption spectrum intensity, information about impurity energy levels by the Urbach energy, and the interaction energy between electrons and phonons under illumination. We also use formulas to determine the conduction band and valence band of the material, thereby providing an energy band structure to explain the mechanisms occurring in the devices.