Rational backbone and ion exchange design for charge stabilization in donor–acceptor polymer thermoelectrics
Journal
Journal of Materials Chemistry A
ISSN
2050-7488
2050-7496
Date Issued
2026
Author(s)
Chang, Chi
Hsiao, Yi-Tso
Lee, Jo-Wei
Chen, Guan-Lin
Tseng, Chi-Chun
Yeh, Li-Lun
Lin, Jhih-Min
Cheng, Yen-Ju
Abstract
Diketopyrrolopyrrole (DPP)-based donor–acceptor copolymers are regarded as promising p-type organic thermoelectrics (OTEs) owing to their high crystallinity and efficient charge transport. However, optimizing their power factor (PF) requires precise control over microstructural ordering, doping efficiency (ηd), and charge carrier stability. Herein, we demonstrate that conjugated breaker units, namely strategically incorporated unfused 2,7-dithienylfluorene (TF) and carbon-bridged fused 2,7-dithienylfluorene, serve as versatile structural motifs for systematically tuning the semicrystalline morphology, dopant accessibility, and energy-level alignment in DPP-based copolymers. Post-doping treatments were performed via FeCl3 oxidation, followed by anion exchange using ionic species of varying ionic radii and coordination characteristics, including lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and 1-ethyl-3-methylimidazolium tetrafluoroborate. This anion-exchange process effectively replaces reactive FeCl4− counterions with more stable ionic species to enhance charge stabilization. Among the tested systems, the TF backbone combined with TFSI− anions exhibited the most favorable structural and electronic compatibility, preserving chain ordering and promoting polaron delocalization. Notably, the LiTFSI-exchanged TF film achieved a PF of 3.31 ± 0.51 µW m−1 K−2 and maintained good stability over 24 h storage. These findings position conjugated breaker design and post-doping ion exchange as synergistic strategies for microstructural optimization and charge carrier stabilization, providing general design principles for the development of stable and processable OTEs.
Publisher
Royal Society of Chemistry (RSC)
Type
journal article