Publication date: 15th December 2025
Thermoelectrics offer the ability to harvest ubiquitous waste heat to power small wearables and Internet of Things (IoT) devices, and they can also function as self-powered heat sensors. However, traditional thermoelectric materials rely on toxic, scarce, or critical raw elements. Organic thermoelectrics (OTE) based on doped conjugated polymers could address this issue, but their performance remains insufficient for most practical applications. Although recently aligned polymers such as PBTTT and DPP have shown great promise, achieving ultra-high power factors, the poor doping stability of conjugated polymers still prevents their reliable operation under ambient conditions. This lack of stability forces researchers to fall back on PEDOT:PSS for any application resembling real-life scenarios, as it remains the only ambient-stable conducting polymer. This reliance slows progress in the field because PEDOT:PSS is already a mature material that appears close to reaching its performance ceiling. Unlocking new breakthroughs in OTEs therefore, requires identifying doping strategies that are preferably not material-specific but instead compatible with a broad range of polymer chemistries, enabling fuller exploitation of the possibilities offered by organic synthesis.
In this presentation, we introduce a doping molecule that provides higher conductivity as well as improved ambient and thermal stability compared to typical molecular dopants—and does so across many prototypical conjugated polymers. We explain the mechanism behind this universal combination of high conductivity and stability using P3HT as a benchmark, supported by Gibbs free-energy simulations of the dopant–polymer system and experimental evidence from GIWAXS (nanostructure evolution) and UV–Vis spectroscopy (doping-state evolution over time). Power factors as high as 65 μW/(m·K2) for PDPP3T and 35 μW/(m·K2) for PBTTT are achieved, remaining as high as 40 μW/(m·K2) and 15 μW/(m·K2), respectively, after 25 days of storage in a glovebox. This represents an order-of-magnitude improvement in stability over state-of-the-art dopants, pointing toward the feasibility of using encapsulated, molecularly doped conjugated polymers in real thermoelectric applications.
The research was further supported by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program: grant agreement 948922 – 3DALIGN. S.G. also acknowledges the support of KU Leuven internal funding for excellent research Interdisciplinary Network (ID-N/21/012).
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