Effect of polymer chain conformation on field-effect transistor performance: synthesis and properties of two arylene imide based D-A copolymers

Two donor-acceptor (D-A) alternating copolymers (P1 and P2) with phthalimide or thieno[3,4-c] pyrrole-4,6-dione as the electron acceptor and bithiophene as the electron donor have been synthesized by Stille polycondensation. Both polymers showed good thermal stability and a low HOMO level. Organic field-effect transistor (OFET) devices with common architectures were fabricated to evaluate and compare the FET properties of the two polymers. Though P2 exhibits better coplanarity than P1, the FET results revealed that both the hole mobility and current on-off ratio of P1 are more than one order of magnitude higher than P2. Theoretical calculations and AFM were conducted to analyze the reason for this very interesting result, and it was found that polymer chain conformation is another important factor (in addition to coplanarity) for polymers to obtain high FET performance.