Mechanically Durable Rare‐Earth Biopolymer Fibers for High‐Efficiency Solar‐Thermal Management

Abstract Bio‐based photothermal fibers offer sustainable and skin‐friendly solutions for personal thermal management. However, their practical deployment is limited by low solar conversion efficiency and weak mechanical properties under extreme conditions. These challenges are addressed by designing biopolymer photothermal fibers (bioPTFs) integrated with Prussian blue‐NaNdF 4 nanocomplexes (NdNCs). The photothermal conversion is greatly enhanced via a cross‐relaxation mechanism, where Nd 3+ energy levels couple with the dye's continuous energy band, boosting non‐radiative decay. Concurrently, the NdNCs induce biomolecular restructuring via salt bridges and hydrogen bonds, increasing β‐sheet content and densifying the crosslinked network. The bioPTFs achieves high photothermal efficiency ( η = 85%) and tensile strength ( σ = 558 MPa), surpassing conventional photothermal fibers. They also exhibits exceptional thermal fatigue resistance, retaining 92% of their tensile strength after 500 cycles under 5‐sun (0.5 W cm −2 ) irradiation. Thin bioPTF fabrics (0.35 mm) show thermal retention similar to 25‐mm down, maintaining 32.4 °C in cold condition. The strategy represents a new paradigm in fiber engineering, with potential for advanced personal thermal management applications.