<p>As the demand for sustainable energy grows, exploring abundant, environmentally friendly materials for high-efficiency solar photovoltaic (PV) technology has become a significant and urgent need in worldwide renewable energy production. In this study, the performance of a novel ZnO/CuO/Cu₂Se heterojunction solar cell was numerically investigated using SCAPS-1D simulation software. The cell’s efficiency was significantly improved through systematic optimization of key parameters, such as bandgap energy, layer thickness, doping concentration, and interface defect density. The output photovoltaic parameters metrics of the designed reference cell, including short-circuit current density of 24.324&#xa0;mA/cm², the open-circuit voltage of 1.132&#xa0;V, the fill factor of 73.15%, and the power conversion efficiency (PCE) of 20.15% were obtained. The maximum PCE of 29.83%, was achieved utilizing a 2&#xa0;μm-thick Cu₂Se absorber layer with bandgap of 1.8&#xa0;eV and doping concentrations of 10¹⁹ cm^-3, 500&#xa0;nm-thick CuO buffer layer with a doping concentration of 10²⁰ cm^-3, and reduced the interface defect density to 10¹⁰ cm^-2. Additionally, the effect of temperature, series and shunt resistance, and contact work functions on the optimized cell’s structure was investigated. These findings demonstrate the potential of ZnO/CuO/Cu₂Se heterojunctions for high-efficiency and eco-friendly thin-film solar cells, providing valuable insights for future research and development in renewable energy technologies.</p>