Tailoring Interfacial Interactions Enables Ultrafast Construction of Conductive Cellulose Film Toward Superior Solar Steam Generation, Wearable Strain Sensor, and Flexible Thermoelectric Power Generator

Cellulose films are known for their sustainability, high flexibility, and outstanding mechanical strength; however, they often exhibit limited optical, electrical, and thermal properties. Conventional modification strategies, such as carbonization or physical blending with conductive materials, tend to be energy‐intensive and often require specialized equipment or controlled environments. In this study, we report an ultrafast coating of PEDOT:PSS onto a unique cellulose/hydroxyapatite substrate, achieved within just 5 s under ambient conditions without the need for any equipment. The incorporation of hydroxyapatite nanowires between cellulose fibers and PEDOT:PSS enhances the interfacial bonding strength by 2.8 times via multiple interactions, enabling such an ultrafast coating process. The resulting composite films effectively combine the excellent water affinity and mechanical robustness of the cellulose/hydroxyapatite substrate with the superior optical, electrical, and thermal properties of the PEDOT:PSS coating. Based on these advantages, we demonstrate multifunctional devices, including solar‐driven water evaporators, wearable strain sensors, and flexible thermoelectric generators, that exhibit competitive performance metrics: a water evaporation rate of 2.02 kg m −2 h −1 , salt rejection (20 wt.% NaCl), stable and rapid sensing toward varying human movements, an electrical conductivity of 465 S m −1 , and a Seebeck coefficient of 28.21 µV K −1 .