Observation of ambipolar field-effect behavior in donor-acceptor conjugated copolymers

Although donor (D)-acceptor (A) conjugated copolymers possess an electron deficient unit, most D-A copolymers exhibit only hole transport properties (p-type). While there are some D-A copolymers that show ambipolarity, n-type behaviour is highly dependent on the type of acceptor used. In this work, ambipolar field-effect behaviour was derived from general D-A conjugated copolymers, believed to be a typical p-type material, by introducing a functional passivation layer between gate dielectric and active layers using polypropylene-co-1-butene (PPcB). The PPcB layer effectively covered the hydroxyl groups and induced a reduction in the energetic disorder at the semiconductor-insulator interface. As a result, the FET devices fabricated using D-A conjugated copolymers, such as PCDTBT, PTBT and Si-PCPDTBT, showed clear ambipolar properties.