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Page 6 of 33 Girase et al. Energy Mater. 2025, 5, 500132 https://dx.doi.org/10.20517/energymater.2025.14

P-type thermoelectric polymers
Conventional p-type TE polymers
[67]
[68]
[69]
The TE performance of various p-type conventional CP including PANI , PPy , polythiophene (PTH) ,
poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) [70-73] , polyacetylene (PA) [74,75] ,
[76]
polycarbazoles (PC) , and their derivatives have been investigated, with their performance metrics
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summarized in Table 1 [20,68,70,76-87] . Generally, the intrinsic conductivities of these CPs range from 10 to
10 S cm , while their k are typically between 0.11 and 0.4 W m K , which contributes positively to their
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[88]
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ZT values . Currently, PF for most polymer-based TE materials falls within the range of 10 μW m K to
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10 μW m K , significantly lower than those of traditional inorganic TE materials [89-92] . Among all these
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conventional TE polymers, PEDOT:PSS is a well-researched p-type TE material notable for its ease of
processing and stability when heavily doped. Despite its promise, excess PSS acts as an insulator, hindering
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charge carrier transport and limiting its TE performance, with σ ranging from 0.012 S cm to 17 S cm and
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PF values from 0.0016 μW m K to 0.9 μW m K -2[70] . Numerous studies have sought to enhance the
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electrical properties of PEDOT:PSS, employing methods such as the introduction of polar solvents such as
dimethylsulfoxide (DMSO) to encourage phase segregation and improve σ. Various post-treatment
techniques have also been developed to optimize the structure and performance of PEDOT:PSS, such as the
use of ionic liquids, reducing agents, and sequential acid-base treatments [72,93,94] .
Research efforts have led to significant improvements in TE performance of PEDOT:PSS. However, PEDOT
derivatives remain promising; challenges such as hygroscopicity and insulating counterions have driven
researchers to explore new p-type TE polymers that may exhibit superior charge-transport characteristics.
Diketopyrrolopyrrole based p-type TE polymers.
DPP has gained considerable attention due to its unique electronic properties and versatility in molecular
design. Its strong electron-accepting features, combined with its high planarity and robust thermal stability,
make it an ideal candidate for enhancing the performance of organic TE devices. Recent advancements in
DPP-based materials have led to significant improvements in charge carrier mobility and thermoelectric
efficiency, paving the way for innovative applications in organic electronics. Figure 4 displays the chemical
structures of several DPP-based p-type D-A polymers and Table 2 summarizes their optimal doped TE
performance.

In 2017, Jung et al. synthesized poly(diketopyrrolopyrrole-terthiophene) (PDPP3T) due to its excellent
performance in field of OFET. The study compares the thermoelectric efficiency of the DPP semiconductor
PDPP3T against conventional thermoelectric polymer poly(3-hexylthiophene) (P3HT). By finely doping
with FeCl , PDPP-3T has higher than 200 μW m K PFs and peaks at 276 μW m K , which is far more
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than the 56 μW m K PF of P3HT. High mobility PDPP3T increases σ without having a high dopant
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volume. It can be highly transparent due to a low band gap in electronic devices. In general, PDPP3T has all
the attributes of high mobility, low band gap and well-controlled doping, to be a new gold standard for
thermoelectric semiconducting polymers . Besides, Liang et al. investigated the doping effects on
[95]
PDPP-4T; they employed the strong oxidative compound Mo(tfd-CO Me) and compared its performance
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to that of FeCl . While Mo(tfd-CO Me) exhibits greater oxidative strength, its larger size as a dopant leads
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to significant disorder within the crystalline portion of the PDPP-4T. This disruption negatively affects the
charge transport pathways, causing poor σ. Consequently, Mo(tfd-CO Me) -doped PDPP-4T exhibited σ of
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approximately 0.3 S cm and a PF of around 15 μW m K . In contrast, FeCl -doped PDPP-4T
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demonstrated much higher conductivity of about 10 S cm and a PF of approximately 23.5 μW m K . This
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comparison highlights that despite the potential advantages of using more powerful oxidants such as
Mo(tfd-CO Me) , the effective doping of CP such as PDPP-4T may rely heavily on the dopant’s size and its
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ability to maintain the integrity of the polymer’s crystalline structure, which is critical for facilitating