Janus Photothermal\nFilms with Orientated Plasmonic Particle-in-Cavity Surfaces Enabling\nHeat Control in Solar-Thermal-Electric Generators

Solar thermoelectric generators (STEGs) consisting of\nsolar absorbers and thermoelectric generators (TEGs) can utilize solar\nenergy to generate electrical power. However, performances of STEGs\nare limited by the heat losses of solar absorbers in air, which become\nmore and more significant with an increase in the solar absorbing\narea. Herein, we describe the preparation of Au@AgPd nanostructure\nmonolayer/poly(vinyl alcohol) (PVA) Janus photothermal films with\nbroadband plasmonic absorption in the visible and near-infrared regions.\nBy uniaxially stretching the Janus film, Au@AgPd can align along the\nstretching direction, which creates particle-in-cavity structures\non the PVA surface. Benefiting from the oriented plasmonic particle-in-cavity\nconfiguration, the Janus films effectively convert sunlight into heat,\ntrap the heat within their micrometer-depth structure, and facilitate\nits transfer along the direction of the nanostructure orientation.\nIntegration of the Janus films with commercial TEGs allows thermal\nconcentration onto a small thermoelectric surface, yielding an open-circuit\nvoltage of 308 mV under 102 mW/cm<sup>2</sup> natural sunlight illumination.\nHeat losses in commercial TEGs integrated with Janus films are reduced\nby approximately 50% while maintaining the same voltage output. Furthermore,\nincorporating the Janus films into a conventional STEG with carbon-based\nsolar absorbers significantly enhances solar-thermal-electric conversion\nperformance, achieving an output power density of 1.3 W m<sup>–2</sup>. Our design of Janus photothermal films with oriented particle-in-cavity\nsurfaces can be extended to various solar-thermal systems for high-efficiency\nsolar energy conversion and heat management.