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.
Kim et al. (Sun,) studied this question.