Cationic species as dopants for organic semiconductors

Organic semiconductors (OSCs) are the potential key materials for future flexible electronics due to their outstanding mechanical and optoelectronic properties1,2 Electronic devices such as organic light emitting diodes have already shown successful progress for flat panel displays, and application of OSCs is gradually expanding to various fields of electronics.1–3 However, OSCs still lag behind inorganic ones due to their poor electrical properties including low charge carrier mobility and conductivity as well as device stability issues.4–7 In order to overcome these issues, several approaches have been developed one of which is doping.5 Doping is one of the most effective methods to improve electrical properties of OSCs through increasing their charge carrier density and mobility.2,8–11 However, the doping of OSCs is different from the doping of inorganic ones. Unlike the latter, doping in organic electronics does not assume the replacement of a host lattice atom by an impurity atom. It is rather a simple charge transfer between two molecules.2,8,9,12–14 A significant number of research groups have reported different kinds of dopants for OSCs. In this review, a summary of the dopants, namely cationic species that can be applied as both pand n-type dopants, is introduced. Cationic dyes as dopants for organic molecules