Interface‐Engineered Wood‐Based Composite Phase Change Materials Integrating Superhydrophobic, Flame‐Retardant, and Antimicrobial Properties for Sustainable Solar–Electric Energy Conversion

ABSTRACT Efficient and durable solar thermal utilization requires composite phase change materials (CPCMs) that integrate high photothermal efficiency, stable energy storage, and environmental robustness within a scalable architecture. However, most CPCMs rely on energy‐intensive processing or carbon‐based frameworks, hindering the simultaneous realization of multifunctionality and sustainability. Herein, a series of carbonization‐free, interface‐engineered bio‐based CPCMs are developed by functionalizing the anisotropic microchannel structure of delignified balsa wood with black phosphorene and metal‐polyphenol network (tannin‐Fe 3+ ). The hybrid interface is further in situ reduced Ag nanoparticles and post‐grafted octadecyl chains, creating a robust superhydrophobic surface. Interfacial regulation improves wood‐based CPCMs compatibility and stability, delivering a latent heat of ∼175.03 kJ kg −1 with suppressed supercooling. Leveraging directional heat pathways, photothermal–plasmonic coupling, and broadband absorption, the CPCMs achieve a photothermal conversion efficiency of 91.27% and a ∼3.9‐fold increase in axial thermal conductivity. The as‐prepared CPCMs further integrates flame retardancy, superhydrophobicity, and antimicrobial activity, thereby mitigating dust adhesion and microbial colonization that would otherwise deteriorate the outdoor photothermal performance. As a proof of concept, stable solar–thermal–electric conversion is demonstrated with an output voltage of up to 0.65 V under one‐sun irradiation. This work presents a scalable and environmentally friendly wood‐based platform for advanced solar thermal energy harvesting.