Co‐Solvent Strategy Enables High‐Performance Printing Organic Thermoelectric via Synergistic Modulation of Crystallinity and Film Homogeneity

Abstract Organic thermoelectric (OTE) hold great promise in printed electrical generator and portable devices, whereas scalable coating is rarely concerned in fabricating high‐performance OTE for the hurdles of coordinating high crystallization and flow homogeneity. In this work, a co‐solvent strategy assisted blade‐coating achieves power factor (PF) breakthrough for P3HT through synergistically modulating the crystallization kinetics and rheological property. By incorporating orthogonal solvent n‐hexane (HEX) into host solvent chloroform (CF), the solubility and pre‐aggregation of P3HT are effectively modulated to promote nucleation/crystal‐growth during film‐forming. Faster P3HT crystal nucleation/growth and relatively slower co‐solvent evaporation endow better‐matched crystallization rates, leading to improved molecular assembly. Combined with crystallization‐inducing effect of multi‐layer blade‐coating, significantly enhanced crystallinity is obtained. In addition, solubility parameters variation alters the molecular arrangements into mix‐orientation, which is beneficial for doping and alleviating the thermoelectric trade‐off. Meanwhile, the viscosity and surface tension of the solution can be accommodated to restrain capillary flow, reinforcing the film uniformity. Consequently, under the optimal co‐solvent ratio of CF:HEX = 7:3 (vol/vol), a conductivity of 605.39 S•cm −1 and a new record PF of 204.62 µW•m −1 •K −2 are reached for P3HT. The study opens a meaningful path for printing high‐performance OTE, revealing the potential for scalable production of OTE architecture.