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Girase et al. Energy Mater. 2025, 5, 500132 https://dx.doi.org/10.20517/energymater.2025.14 Page 15 of 33

orientations. This would imply more space where the dopants could reside, capable of ensuring more
effective and even doping within the film. As a result of these structural advantages, PDPF demonstrated
much higher σ and PF values compared to PDPH. The TE performance resulted in a maximum σ of 1.30 S
-2
-1
cm with a PF of 4.65 μW m K for PDPF. In contrast, the less effective doping profile allowed for only a σ
-1
of 1.01 × 10 S cm with a PF of 5.11 × 10 μW m K for PDPH. Later, Yan et al. designed and synthesized
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-4
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a more electron-deficient structural backbone based on DPP, entitled PzDPP and its polymer P(PzDPP-
CT2) . The polymer was designed by substituting the bithiophene units in P(TDPP-CT2) with pyrazine
[123]
moieties and copolymerizing it with a cyano-functionalized bithiophene as an electron-deficient moiety.
The resultant polymer P(PzDPP-CT2) exhibited a much lower E LUMO of -3.45 eV compared to -2.85 eV for
dibenzothiophene and -3.06 eV for pyridine flanked-DPP (PyDPP). The introduction of the pyrazine unit
gave rise to considerable intramolecular hydrogen bonding, which helped the polymers gain additional
rigidity and planarity in their backbones. Such structural enhancements resulted in efficient charge
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2
transport along the chains, leading to 0.79 cm V s electron mobility (μ ) for P(PzDPP-CT2), which was
e
significantly higher than the above-mentioned 0.32 cm V s for P(TDPP-CT2). This enabled P(PzDPP-
2
-1 -1
CT2) to achieve an excellent maximum σ of 8.4 S cm and PF of 57.3 μW m K , marking the highest
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performance reported for DPP-based n-type TE materials. Furthermore, Yan et al. computationally
designed a new pyrazine-based polymer, P(PzDPP-2FT), which features fluorine substitutions at the
thiophene sites . This novel structure benefits from the presence of intrachain noncovalent hydrogen
[145]
bonding interactions between the DPP, pyrazine, and fluorine units. One of the many interesting features of
P(PzDPP-2FT) is that it tolerates disorder caused by doping. In fact, the original paracrystalline structure
was retained when up to 60% concentration was reached with N,N-dimethylbenzimidazole (N-DMBI). This
remains a highly relevant characteristic as it enhances the stability and performance of the polymer through
heavy doping conditions. Furthermore, when P(PzDPP-2FT) is doped with cobalt cyclopentadienyl (CoCp )
2
, its σ significantly improves, achieving a value of 129 S cm .
-1
Recently, Wang et al. designed and synthesized new n-type TE polymers using novel approach that is
development of A-A polymers designed strategy. This A-A strategy will help reduce intramolecular charge
transfer (ICT) properties that influence the performance of semiconductors achieved with low FMOs.
Therefore, they synthesized two A-A polymers based on this strategy namely, PDCNBT-DPP and
PDCNBSe-DPP by integrating DPP with coplanar building block and cyano-functionalized
benzothiadiazole (DCNBT) and benzoselenadiazole (DCNBSe) possessing high electron deficiency . The
[146]
synthesized polymers demonstrated very narrow bandgaps (~1.0 eV) and deep-lying LUMO energy levels of
~-3.90 eV, thus leading to n-type behavior within the OTE devices. The highest electrical conductivities,
11.78 and 12.36 S cm , are displayed by PDCNBT-DPP and PDCNBSe-DPP following N-DMBI-H doping,
-1
respectively, contributing to high PFs of 7.96 and 9.22 μW m K . Relatively higher PF value obtained for
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the PDCNBSe-DPP than PDCNBT-DPP attributed to decrease in aromaticity and increase in quinodal
nature of the acceptor unit when S was replaced with Se. Moreover, the PDCNBSe-DPP has low LUMO
energy levels and high electron mobility than PDCNBT-DPP. These results highlight the fact that cyano-
substituted benzoselenadiazole insertion into A-A-type polymers is a successful strategy for building high-
performance n-type OTEs.

Shi et al. synthesized a new high-performance n-type homopolymer PTz-5-DPP, using firstly adopted C-H/
C-H oxidative direct arylation polycondensation method using newly developed monomer 3,6-di(thiazol-5-
yl)-diketopyrrolopyrrole (Tz-5-DPP). The polymer has demonstrated significant potential as an n-type OTE
application. The PTz-5-DPP polymer displays both edge-on and face-on orientations in thin films with
stable lamellar (22 Å) and π-π stacking (3.62 Å) distances prior to and after doping. After doping with
N-DMBI, the crystallinity of the polymer was enhanced considerably as revealed through stronger and