n‐Type Semiconductor Hydrogels for Tunable Organic Electrochemical Transistors Operation and Evaporation‐Driven Synergistic Energy Harvesting and Thermal Management

ABSTRACT n‐type organic semiconductors (n‐OSCs) hydrogels with ion‐electronic conductivity and adjustable mechanical properties are essential for sophisticated bioelectronic systems and evaporative hydrovoltaic/thermoelectric generators. Integrating efficient energy harvesting and low‐power bioelectronics in n‐OSC hydrogels is hindered by an intrinsic conflict between high conductivity and depletion‐mode operation. In this work, a multifunctional n‐OSC hydrogel platform comprising poly(benzodifurandione) (PBFDO)/polyacrylic acid is prepared via solvent exchange and ionic liquid‐mediated phase separation. The porous network enables continuous electron transport and enhanced electrical performance through component modulation. For energy harvesting, the hydrogel achieves evaporation‐driven hydrovoltaic‐thermoelectric power generation utilizing evaporative cooling‐induced temperature gradients and the intrinsic thermopower of the PBFDO backbone. The thermally induced voltage reaches up to 30 mV/K, exceeding its intrinsic thermoelectric response by over three orders of magnitude. Furthermore, a controlled chemical dedoping strategy is employed to mitigate the high static power consumption of organic electrochemical transistors (OECTs). This successfully switches OECTs operation from depletion to accumulation mode, enhancing the on/off ratio by one order of magnitude, shifting the threshold voltage from −0.66 to −0.16 V, and modulating hysteresis. This work advances the tunability of n‐OSC hydrogels, facilitating their future use in sophisticated bioelectronics, thermal management, and self‐powered systems.