Enhancing Field-Effect Mobility of Conjugated Polymers Through Rational Design of Branched Side Chains



The design of polymer semiconductors possessing effective π–π intermolecular interactions coupled with good solution processability remains a challenge. Structure-property relationships associated with side chain structure, π–π intermolecular interactions, polymer solubility, and charge carrier transport are reported for a donor–acceptor(1)-donor–acceptor(2) polymer: 5-Decylheptadecyl (5-DH), 2-tetradecyl (2-DT), and linear n-octadecyl (OD) chains are substituted onto a polymer backbone consisting of terthiophene units (T) between two different electron acceptors, benzothiadiazole (B), and diketopyrrolopyrrole (D), pTBTD, to afford pTBTD-5DH, pTBTD-2DT, and pTBTD-OD, respectively. In the 5-DH side chain, the branching position is remote from the polymer backbone, whereas it is proximal in 2-DT. This study demonstrates that incorporation of branched side chains where the branching position is remote from the polymer backbone merges the advantages of improved solubility from branched units with effective π–π intermolecular interactions normally associated with linear chains on conjugated polymers. pTBTD-5DH exhibits superior qualities with respect to the degree of polymerization, solution processability, π–π interchain stacking, and charge carrier transport relative to the other analogs. pTBTD-5DH exhibits a field-effect hole mobility of up to 2.95 cm2 V–1 s–1, a factor of 3–7 times that achieved with pBDT6-DT and pBDT6-OD.