Herein, we report the direct aqueous synthesis of AlSe quantum dots (QDs) via a combination of chemical precipitation and hydrothermal methods. These quantum dots were subsequently deposited onto a TiO₂ nanoparticles substrate via the drop-casting method. Then, the effect of incorporating Mn2⁺ and Co2⁺ ions into the CdS layer on the photovoltaic performance of AlSe quantum dot-sensitized solar cells (QDSSCs) was investigated. Manganese- and cobalt-doped CdS thin films, with doping concentrations of 2%, 4%, and 6%, were prepared using the successive ionic layer adsorption and reaction (SILAR) technique. X-ray diffraction (XRD) analysis of pure CdS, Mn-doped CdS, and Co-doped CdS thin films revealed a cubic crystal structure, indicating that doping does not alter the crystal lattice of CdS. Both Mn2⁺-doped and Co2⁺-doped CdS layers exhibited a red-shift in the absorption edge compared to the undoped CdS layer, extending the light absorption range and enhancing the current density. The doped CdS nanoparticles also modified the photoanode structure, leading to an increase in the short-circuit current density (Jsc) from 15.93 mA/cm2 for the undoped TiO₂/AlSe/CdS/ZnS photoanode to 21.31 mA/cm2 for TiO₂/AlSe/CdS:Mn(4%)/ZnS and 24.62 mA/cm2 for TiO₂/AlSe/CdS:Co(4%)/ZnS photoelectrodes. Consequently, the power conversion efficiency (PCE) of the QDSSCs was improved significantly, reaching 6.00% for TiO₂/AlSe/CdS:Co(4%)/ZnS photoanode, compared to those of 4.69% and 3.85% for TiO₂/AlSe/CdS:Mn(4%)/ZnS and undoped TiO₂/AlSe/CdS/ZnS structures, respectively.
