Thiazoloisoindigo-based Polymer Semiconductors: Synthesis, Structure-Property Relationship, Charge Carrier Polarity, and Field-Effect Transistor Performance

Developing new polymeric semiconductors with excellent device performance is essential for organic electronics. Herein, we synthesized two new thiazoloisoindigo (TzII)-based polymers, namely, P(TzII-dTh-dTh) and P(TzII-dTh-dTz), by copolymerizing thiophene-flanked TzII with bithiophene and bithiazole, respectively. Owing to the more electron-deficient nature of bithiazole than bithiophene, P(TzII-dTh-dTz) possesses deeper LUMO/HOMO levels of −3.45/−5.47 eV than P(TzII-dTh-dTh) (−3.34/−5.32 eV). The organic field-effect transistor (OFET) devices based on P(TzII-dTh-dTh) exhibited p-type behaviors with an average hole mobility value as high as 1.43 cm 2 ·V −1 ·s −1 , while P(TzII-dTh-dTz) showed typical ambipolar characteristics with average hole and electron mobilities of 0.38 and 0.56 cm 2 ·V −1 ·s −1 . In addition, we compared the performances of both polymers with other TzII-based polymers reported in our previous work, and showed that the charge carrier polarity can be manipulated by adjusting the number of the thiophene units between the acceptor unit. As the increase of the number of thiophene rings, charge carrier polarity shifts from electron-dominated ambipolar transport to hole-dominated ambipolar transport and then to unipolar hole transport in OFETs, which provides an effective molecular design strategy for further optimization of polymer OFET performance.