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Page 22 of 33 Girase et al. Energy Mater. 2025, 5, 500132 https://dx.doi.org/10.20517/energymater.2025.14

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7.8 S cm having been reported [129,139,165] . Its volatility renders it difficult to manage doping, and doped
[166]
systems are found to be unstable even under inert conditions, thereby limiting long-term application . In
contrast, tetrabutylammonium salts (TBAX, X = F , OH , CH COO , etc.) provide a more solution-
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processable and stable pathway. For instance, tetrabutylammonium fluoride (TABF) reacts with electron-
deficient polymers such as chloro-benzodifurandione-phenylenevinylene (ClBDPPV) to give (polymer-F )
-
complexes that act as electron donors . Annealing 25 mol% TBAF-doped ClBDPPV films at 130 °C for 12
[167]
h produced σ of 0.62 S cm , demonstrating exceptional air stability, maintaining greater than 0.1 S cm after
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one week. Among them, N-DMBI remains the most effective and versatile dopant, especially in doping
DPP-based thermoelectric polymers. Recent studies have demonstrated the ability of DPP-based polymers
such as P(PzDPP-CT2), PTz-5-DPP, ThDPP-CNBTz, and pDFSe, all of which were doped effectively with
N-DMBI. These polymers have exhibited superior TE performance due to their electron-deficient
backbones, strong intermolecular interactions, and good doping compatibility. For instance, P(PzDPP-CT2)
has pyrazine and cyano-functionalized bithiophene moieties, which provide σ = 8.4 S cm and PF = 57.3 μW
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m K . PTz-5-DPP, synthesized via oxidative direct arylation polycondensation, provides a very high PF
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value of ~106.0 μW m K . Even more impressively, ThDPP-CNBTz with a thiophene-flanked DPP
backbone provides σ = 50.6 S cm and PF = 126.8 μW m K upon N-DMBI doping. But the most
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surprising performance comes with pDFSe, a noncovalently fused-ring-designed polymer, that facilitates
charge transport in disordered films with a record-high value of σ at 62.6 S cm and PF of 133.1 μW m K .
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The results show that it is the cooperation of well-designed polymer architectures and good n-dopants such
as N-DMBI that provide the solution for further improving organic TE devices.
The air stability of n-type CP remains a challenge for its practical application in OTEs. Unlike their p-type
counterparts, the majority of n-type polymers are stable under inert atmospheres only since organic anions,
particularly carbanions, are susceptible to oxidative degradation. The reaction rapidly quenches mobile
[128,168]
electrons and decreases σ . One of the potential approaches for preventing this problem is the synthesis
of polymers with deep levels of LUMO (typically lower than -4.7 eV), reducing energy offset to oxidative
degradation [169,170] . In order to get over this, strategies such as locating electron-deficient groups on the
polymer backbone and employing dopants that form stable charge-transfer complexes have proven useful.
For instance, recently, PTz-DPP-based TE polymers have shown deepened LUMO levels with higher
nitrogen content which directly affect the DOS, making it easier for polaron formation and leading to
improved charge transport properties . In addition, designing a thicker dopant or film layer enriched on
[151]
the surface might utilize a self-encapsulation effect, preventing physical oxygen and moisture entry. For
example, 3-8 μm thick ClBDPPV films doped with 25 mol% TBAF retained over 0.1 S cm conductivity
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even after exposure to air for one week, showing the potential of combinations of low-LUMO polymers
with stable dopants . In combination, synergistic polymer chemistry design, dopant selection, and film
[167]
morphology are required to achieve both high performance and stable durability for n-type OTE materials.

COMPARATIVE STUDY ON DPP-BASED THERMOELECTRIC POLYMERS
Comparative study in p-type DPP-based thermoelectric polymers
In a comparative study of p-type DPP-based thermoelectric polymers, PDPP-4T-EDOT, PDPPSe-12 and
P29DPP-BTOM emerge as potential candidates, each excelling in different performance metrics. PDPP-4T-
EDOT realizes a remarkably high PF of 298.2 μW m K at an optimal doping concentration of 0.5 mM.
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This work highlights that the incorporation of electron-rich EDOT moiety into a DPP framework results in
significant enhancement of the electronic characteristics of the polymer, significantly outpacing other
contenders such as PDPP-3T and P29DPP-BTOM. The EDOT incorporation increases the HOMO levels,
allowing efficient p-doping without sacrificing high coplanarity and charge carrier transport characteristics.
PDPPSe-12 is a selenium-substituted DPP-selenophene copolymer with strong intermolecular forces and
stable morphology due to the larger atomic radius of selenium. PDPPSe-12 exhibited high hole mobility