The rapid growth of the global population and the increasing demand for energy, coupled with the urgent need for environmental conservation, have prompted researchers to explore renewable energy sources as viable alternatives to non-renewable fossil fuels. This study evaluates the performance enhancement of photovoltaic/thermal (PVT) systems using an immersion cooling method with copper oxide nanofluids. The experimental setup included a glass chamber immersing the panel surface, tested at nanofluid volume ratios of 0.025% and 0.05%, and flow rates of 0.01 and 0.02 L s-1. The immersion height was 5 cm within the glass chamber. The tests were conducted under ambient conditions, which included an ambient temperature of 20.6-31.2 ℃ and an irradiance of 343-924 W m-2. Results demonstrate that copper oxide nanofluids at a 0.05% volume ratio and a 0.02 L s-1 flow rate improved thermal efficiency to 31.87% and reduced panel surface temperature by up to 11.8 °C compared to water cooling. Also, the electrical efficiency of the PVT system exceeded that of the reference panel. The overall efficiency of the PVT system reached 41.89%. These findings highlight the potential of nanofluid-based cooling to optimize PVT system efficiency by enhancing thermal management.