Abstract: With socioeconomic development and advancements in science and technology, solar energy has garnered widespread attention due to its inherent advantages, such as being clean and renewable; its utilization primarily involves photovoltaic and photothermal conversion. This study employs a combination of the Monte Carlo method and Mie theory to establish a flat-plate transmission model, investigating the impact of TiO2 nanofluid volume fractions—specifically 0.0001%, 0.0005%, 0.001%, 0.005%, 0.01%, and 0.05%—on the system"s radiative characteristics and efficiency. The results indicate that as the nanofluid volume fraction increases, the absorptance of the fluid layer rises continuously, while that of the photovoltaic layer steadily declines. The absorptance reaches its maximum value at a volume fraction of 0.05%, approaching 0.98 within the 1.35–1.50 μm wavelength band. By examining the influence of nanofluid volume fraction on the system"s absorption characteristics and energy distribution, this study provides a valuable reference for selecting appropriate nanofluid concentrations across various application scenarios.