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Bi-thieno[3,4-c]pyrrole-4,6-dione (bi-TPD) and oligothiophene copolymer semiconductors P1–P4, with different alkyl side chain densities and orientations, were synthesized. Their physicochemical properties were systematically characterized. With trimethoxy(octadecyl)silane (OTMS) modified SiO2 as substrates, the as-spun thin films of P1, P3 and P4 adopted the face-on packing structure while the P2 films displayed the edge-on packing arrangement. The packing differences of P1–P4 were ascribed to their different alkyl chain densities and orientations. The higher alkyl chain density is favorable to the face-on packing structure. After thermal annealing, the packing orientation of P2 remained and the packing structures of P1, P3 and P4 changed. P1 and P4 based films exhibited the coexistence of the edge-on and face-on packing structures in which the edge-on structure was predominant, and P3 based thin films were converted to the edge-on packing arrangement. The relationship between the aggregation structures and charge carrier transport properties of these films was explored through thin film transistors. All devices exhibited p-channel behavior with a maximum mobility larger than 1.0 cm2 V−1 s−1. Interestingly, the P3 films with face-on packing structures displayed a high mobility up to 1.18 cm2 V−1 s−1 (average mobility of 1.02 cm2 V−1 s−1), very close to the edge-on packed films which showed a maximum mobility of 1.4 cm2 V−1 s−1 (average mobility of 1.16 cm2 V−1 s−1). These results demonstrated, similar to edge-on packing structures, the face-on packing arrangement with π–π interactions facilitated charge carrier transport.

Two novel polymers PDPP3T-CN and PDPPTPT-CN containing nitrile-substituted thienyl and phenyl units were designed and synthesized. The influence of nitrile groups on the electronic properties and charge-carrier transport of the polymers was thoroughly investigated and highlighted by comparing with the corresponding non-nitrile substituted polymers. Experimental results showed that the introduction of nitrile groups lowered the HOMO and LUMO energy levels of polymers by about 0.3 eV and 0.2 eV, respectively. Thin film transistor characteristics displayed that both polymers exhibited electron-dominated ambipolar behavior under ambient conditions. The highest electron/hole mobilities were 0.18/0.0083 cm2 V−1 s−1 for PDPPTPT-CN and 0.09/0.0017 cm2 V−1 s−1 for PDPP3T-CN, one of the highest electron mobilities for DPP-based polymers measured under ambient conditions with bottom-gate/top-contact device configurations.