Molecular Design of Diketopyrrolopyrrole-Based Donor-Acceptor Copolymers via Backbone and Polar Side Chain Engineering for Enhanced Thermoelectric Properties

Achieving high thermoelectric performance in conjugated polymers remains a critical challenge because chemical doping often disrupts molecular packing and induces electronic disorder, limiting the simultaneous enhancement of electrical conductivity and the Seebeck coefficient. In this presentation, we introduce a rational molecular design strategy for diketopyrrolopyrrole (DPP)-based donor-acceptor copolymers based on systematic modulation of the conjugated backbone and polar side-chain architecture. The introduction of polar side chains and electron-rich donor units enables the modulation of energy levels, dopant-polymer interactions, and interchain packing, which collectively facilitates efficient charge generation and transport. However, the doped microstructures are highly dependent on the specific balance between backbone structure and side-chain polarity. Excessive dopant interactions can lead to structural disorder and unfavorable doping behavior, highlighting the importance of optimizing both doping efficiency and microstructural robustness. Among the investigated copolymers, the optimized molecular structure achieved an optimized balance between dopant accessibility and ordered charge-transport pathways, resulting in concurrent improvements in electrical conductivity and seebeck coefficient. Consequently, a high power factor of 561.9 µW m⁻¹ K⁻² is achieved, representing one of the highest values reported for DPP-based conjugated polymers. These findings establish backbone and polar side-chain engineering as an effective molecular design strategy for addressing the intrinsic trade-off between doping efficiency and structural order. This approach provides molecular-level design principles for high-performance organic thermoelectric materials.