Solvent-Mediated Reactivity Control of Lewis-Paired Dopants for Efficient and Stable Doping of Organic Semiconductors

Molecular p-doping is essential for optimizing the electrical properties of organic semiconductors (OSCs) for thermoelectric and organic (opto)electronic devices. Recently, Lewis-paired dopants, formed by coordinating Lewis acids with cyano-functionalized acceptors, have emerged as promising organic dopants owing to their deep LUMO levels, strong oxidation ability, and excellent thermal stability.[1] However, their high reactivity complicates precise doping-level control. Moreover, Lewis-paired dopants are efficiently generated only in non-polar solvents, which readily dissolve pre-coated OSC films during solution sequential doping (SqP), limiting practical applications.

Herein, a solvent-mediated strategy is introduced to regulate Lewis-paired dopant reactivity by controlling the association-dissociation equilibrium between Lewis acids and solvent molecules. Spectroscopic analyses and theoretical calculations reveal that highly polar solvents strongly coordinate with Lewis acids, suppressing Lewis-paired dopant formation, whereas lower-polarity solvents promote controlled dopant generation during film processing. Consequently, moderately polar orthogonal solvents enable efficient doping while preserving the molecular ordering of OSC films.

Using this strategy, finely tunable and efficient doping was achieved across various OSCs, including polymers that are difficult to dope using conventional methods. The optimized films exhibited superior thermoelectric performance, outperforming the conventional FeCl₃ dopant while providing markedly improved thermal and ambient stability. This work provides mechanistic insights into Lewis-paired dopant formation and presents a simple, versatile strategy for controllable and stable molecular doping, paving the way for high-performance organic thermoelectrics and flexible organic electronics.