Solvent-Mediated Reactivity Control of Lewis-Paired Dopants as a Versatile Strategy for Tunable and Stable Doping of...

The Lewis pairing between existing dopant molecules offers great potential for developing new organic dopants with exceptional doping strength and stability. However, the high reactivity of Lewis-paired dopants complicates doping-level control, while the use of non-orthogonal solvents can damage organic semiconductor (OSC) films, hindering device applications. Here, the dopant reactivity is controlled by regulating the association-dissociation kinetics among pairing dopants and solvent molecules, which are strongly influenced by solvent polarity. In highly polar solvents, Lewis acid-solvent adducts predominantly form, suppressing the generation of Lewis-paired dopants. As solvent polarity decreases, the dissociation rate of the Lewis acid-solvent adduct increases, establishing a dynamic equilibrium between the Lewis acid and the solvent and thereby optimizing reactivity. Consequently, the optimally processed Lewis-paired dopant enables efficient doping of various OSCs with finely tunable doping levels, simultaneously achieving a high thermoelectric power factor (170 µW m^-1 K^-2) and Seebeck coefficient (227 µV K^-1). These performances surpass those of the conventional salt-type FeCl₃ dopant and exhibit markedly improved doping stability under ambient and elevated-temperature conditions. This study provides a practical strategy for utilizing Lewis-paired dopants by elucidating their doping mechanisms, paving the way to overcome long-standing limitations in OSC doping.