0.34 emissivity surface using a hot mirror and directional heat conduction for photothermal energy storage

Photothermal conversion phase-change materials (PCPCMs) effectively harvest and store solar thermal energy but suffer from high radiative losses due to their intrinsic infrared emissivity. Here, we report a bidirectional thermal regulation approach integrating spectrally selective low-infrared-emissivity surfaces with directional thermal transport channels to address this issue. This design achieves a mid-infrared emissivity of 0.34 on the surface and a 65% enhancement in internal heat transfer while maintaining enthalpy with negligible reduction. A photothermal physical model with a cutoff wavelength accurately quantifies the convective and radiative losses induced by the hot mirror. The results reveal that the heat dissipation pathway shifts from radiation dominated to convection dominated, leading to a 76% reduction in radiative loss and a 27% improvement in photothermal conversion efficiency. This work decouples optical absorption from thermal emission, providing an efficient and generalizable route for high-performance solar thermal energy harvesting and storage systems.