Molecular conformational modulation via intramolecular non-covalent interactions enables a good balance of crystallinity and doping efficiency in DPP-based polymer thermoelectrics

Abstract

The electrical conductivity (σ) of polymeric thermoelectric materials is severely constrained by the trade-off between optimizing crystallinity and achieving high doping efficiency. Conventional tactics for addressing this issue tend to adopt the side-chain engineering or backbone rigidification, which frequently compromise σ. Herein, we proposed a conformational modulation strategy to leverage the intramolecular non-covalent interactions for decoupling the crystallinity from the doping kinetics. A dual-acceptor copolymer, P(2ThDPP-BTZ), was designed and synthesized by integrating a benzothiadiazole (BTZ) acceptor unit into a thiophene-substituted diketopyrrolopyrrole (2ThDPP)-based backbone. Although the BTZ incorporation slightly deepened the HOMO energy level, it would induce the directional intramolecular S···N interactions with the adjacent 2ThDPP segments, resulting in a slightly curved S-shaped planar conformation. Compared with the rigid linear homopolymer P(2ThDPP), such a conformational modulation enhanced the dopant permeation and the diffusion kinetics with no significant compromise in the polymeric crystallinity for charge transport. Consequently, the FeCl₃-doped P(2ThDPP-BTZ) achieved the superior doping kinetics and a higher doping level, thereby enhancing its thermoelectric performance. This work provides a new insight into molecular design strategies in advanced electronic materials through conformational modulation.