n-Doped conjugated polymers usually show low electrical conductivities and low thermoelectric power factors, limiting their applications in n-type organic thermoelectrics. Here, we report the synthesis of a new diketopyrrolopyrrole (DPP) derivative, pyrazine-flanked DPP (PzDPP), with the deepest LUMO level in all the reported DPP derivatives. Based on PzDPP, a donor−acceptor copolymer, P(PzDPP-CT2), is synthesized. The polymer displays a deep LUMO energy level and strong interchain interaction with a short π−π stacking distance of 3.38 Å. When doped with n-dopant N-DMBI, P(PzDPP-CT2) exhibits high ntype electrical conductivities of up to 8.4 S cm −1 and power factors of up to 57.3 μW m −1 K −2 . These values are much higher than previously reported n-doped DPP polymers, and the power factor also ranks the highest in solution-processable n-doped conjugated polymers. These results suggest that PzDPP is a promising high-performance building block for n-type organic thermoelectrics and also highlight that, without sacrificing polymer interchain interactions, efficient n-doping can be realized in conjugated polymers with careful molecular engineering.

Doping has been widely used to control the charge carrier concentration in organic semiconductors. However, in conjugated polymers, n-doping is often limited by the tradeoff between doping efficiency and charge carrier mobilities, since dopants often randomly distribute within polymers, leading to significant structural and energetic disorder. Here, we screen a large number of polymer building block combinations and explore the possibility of designing n-type conjugated polymers with good tolerance to dopant-induced disorder. We show that a carefully designed conjugated polymer with a single dominant planar backbone conformation, high torsional barrier at each dihedral angle, and zigzag backbone curvature is highly dopable and can tolerate dopant-induced disorder. With these features, the designed diketopyrrolopyrrole (DPP)-based polymer can be efficiently n-doped and exhibit high n-type electrical conductivities over 120 S cm−1, much higher than the reference polymers with similar chemical structures. This work provides a polymer design concept for highly dopable and highly conductive polymeric semiconductors.

Doping of polymeric semiconductors limits the miscibility between polymers and dopants.A lthough significant efforts have been devoted to enhancing miscibility through chemical modification, the electrical conductivities of n-doped polymeric semiconductors are usually below1 0Scm À1 .W e report adifferent approach to overcome the miscibility issue by modulating the solution-state aggregates of conjugated polymers.Wefound that the solution-state aggregates of conjugated polymers not only changed with solvent and temperature but also changed with solution aging time.M odulating the solution-state polymer aggregates can directly influence their solid-state microstructures and miscibility with dopants.A s ar esult, both high doping efficiency and high charge-carrier mobility were simultaneously obtained. The n-doped electrical conductivity of P(PzDPP-CT2) can be tuned up to 32.1 Scm À1 .T his method can also be used to improve the doping efficiency of other polymer systems (e.g. N2200) with different aggregation tendencies and behaviors.