Toward High Performance Ambipolar Transport from Super-exchange Perspective: Theoretical Insights for IID-based Copolymers

High-performance ambipolar charge transport materials can reduce the manufacturing cost of OFET and OPV devices, and simplify circuit design and device structure. In order to obtain ambipolar donor-acceptor (D-A) polymer, many efforts have been made through different donor and acceptor combination, halogenation or heteroatom substitution. However, the influencing factor for charge transport polarity is still much complicated. Based on intra-chain super-exchange mechanism for D-A polymer, we found that the energy alignment of donor and acceptor moiety has large impact on charge transport polarity. When the HOMO-LUMO (H-L) gap of the acceptor moiety is narrow, its HOMO/LUMO energy level both lie between the HOMO and LUMO of the donor moiety (sandwich-type energy alignment), and the corresponding D-A copolymers will be more likely ambipolar transport. And thus, take a narrow H-L gap thiazoleisoindigo (TzIID) acceptor as an example, we demonstrated that a series of TzIID based copolymers combined with wide H-L gap donor moieties can reveal ambipolar transport. We further predict several high performance ambipolar D-A copolymers (TzIID-TT etc.) with balanced electron and hole transport, whose effective mass (me*=0.146 and mh*=0.128) is one of the smallest effective masses among ambipolar materials.