Radiative cooling technology shows promise for improving thermoelectric generator (TEG) efficiency, but challenges in hot-end design and model validation remain. To address this, a Janus moth-eye-inspired device was developed, leveraging microstructure-enhanced absorption/emission. This device combines a SiO₂ radiative cooler with a radiative Si photothermal absorber in a synergistic configuration. When integrated into a commercial TEG for gradient-based power generation, the Janus composite demonstrated exceptional performance: a peak output voltage of 108 mV, an average daytime voltage of 70 mV under summer daylight conditions, and an output power density reaching 41.5 μW/cm². This study systematically investigates the key parameters of the Janus structure and their impact on the voltage output. Furthermore, it experimentally validates the efficacy of both the SiO₂ radiative cooler and Si photothermal absorber in boosting TEG performance. These findings establish a foundation for future research on stable, rigid biomimetic microstructured thin films for advanced thermoelectric applications.