<p>The performance of a nanofluid-filtered PV/T system largely depends on the properties of the selected nanofluid. In this study, Fe₃O₄@SiO₂ nanofluid is synthesized via the sol-gel method, and its optical and thermal properties are systematically evaluated. Optical tests show that Fe₃O₄@SiO₂ nanofluid exhibits high transmittance in the 650–1075 nm wavelength range and strong absorbance in the visible spectrum. Thermal stability tests under continuous heating confirm its suitability as an optical filter for PV/T systems. Indoor experiments are conducted to assess the effects of Fe₃O₄@SiO₂ nanofluid on the performance of filtered PV/T systems at varying mass concentrations and optical thicknesses. The results indicate optimal system performance with an optical thickness of 2 cm and a mass concentration of 50×10^–6, achieving an MF (merit function) value of 1.802. Subsequently, flow rate experiments are performed to evaluate thermal efficiency and MF across various flow rates. At a flow rate of 6 mL/min, thermal efficiency reaches 79.4%, and the MF value increases to 2.34. Additionally, the Fe₃O₄@SiO₂ nanofluid optical filter significantly reduces the operating temperature of photovoltaic cells. After one hour of illumination, the PV cell temperature decreases by 36.43%, mitigating thermal-induced performance degradation. These findings provide a solid foundation for the optimization and practical application of filtered PV/T systems.</p>