N-Type Doping of Naphthalenediimide-Based Random Donor-Acceptor Copolymers to Enhance Transistor Performance and Structural Crystallinity.

An integrated strategy of molecular design and conjugated polymer doping is proposed to improve the electronic characteristics for organic field effect transistor (OFET) applications. Here, a series of soluble naphthalene diimide ()-based random donor-acceptor copolymers with selenophene π-conjugated linkers and four acceptors with different electron-withdrawing strengths (named as ///) are synthesized, characterized, and used for OFETs. N-type doping of -based random copolymers using (12,18)-5,6,12,12,13,18,18,19-octahydro-5,6-dimethyl-13,18[1',2']-benzenobisbenzimidazo[1,2-:2',1'-]benzo[][2.5]benzodiazocine potassium triflate adduct () is successfully demonstrated. The undoped , , and samples exhibit ambipolar charge transport, while presents only a unipolar n-type characteristic. Doping with significantly modulates the performance of / OFETs, with a 3- to 6-fold increase in electron mobility (μ) for 1 wt % doped device due to simultaneous trap mitigation, lower contact resistance (), and activation energy (), and enhanced crystallinity and edge-on orientation for charge transport. However, the doping of intrinsic pro-quinoidal / films exhibits unchanged or even reduced device performance. These findings allow us to manipulate the energy levels by developing conjugated copolymers based on various acceptors and quinoids and to optimize the dopant-polymer semiconductor interactions and their impacts on the film morphology and molecular orientation for enhanced charge transport.