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Page 16 of 33 Girase et al. Energy Mater. 2025, 5, 500132 https://dx.doi.org/10.20517/energymater.2025.14

sharper X-ray diffraction (XRD) peaks and larger lamellar coherence length from 68.9 Å (undoped) to 132.0
Å (50 wt% doped). From the AFM, they observed smooth surface in the undoped film (RMS 0.62 nm), while
doped films exhibit granular morphology and a moderate roughness increase (up to 1.69 nm), indicating
more ordered molecular packing without the formation of large aggregates. However, in general polymers
with low crystallinity tend to have more disordered or flexible structures, which makes it easier for dopant
molecules to mix in within the polymer matrix, but in the case of PTz-5-DPP, the polymer shows bimodal
packing orientations. These mixed orientations naturally create transitional regions or interfaces between
the two packing types. These regions can act as flexible zones that help to accommodate dopant molecules.
Upon doping with N-DMBI, PTz-5-DPP achieved an impressive electron conductivity exceeding
-1
-1
8.38 S cm . Moreover, it achieved a PF reaching up to 106.0 μW m K -2[147] .
For thermoelectric applications, Tu et al. developed a novel class of structurally easy, low-cost, and easily
available electron-deficient structural moiety for n-type polymers. They have come up with 3,6-
dibromopyrazine-2-carbonitrile (CNPz) and 3,6-dibromopyrazine-2,5-dicarbonitrile (DCNPz), two cyano-
functionalized pyrazine electron-deficient building blocks. Their great planarity is a major advantage for
their use in n-type systems since the steric hindrance effect on the cyano-functionalized pyrazine building
blocks has been theoretically studied. Two A-A type polymers, P(DPP-CNPz) and P(DPP-DCNPz), were
synthesized from CNPz and DCNPz through incorporating them with the DPP unit . The planar
[148]
backbones and deep-lying LUMO levels of these polymers aid in the achievement of high n-type
-1
performance. The polymers exhibited unipolar electron mobilities of up to 1.85 cm V s for P(DPP-
2
-1
-1
2
-1
DCNPz) and 0.85 cm V s for P(DPP-CNPz). When doped with the molecular dopant N-DMBI, they
revealed high PFs of 41.4 μWm K and 30.4 μWm K , along with outstanding electrical conductivities of
-2
-1
-2
-1
-1
25.30 S cm and 33.93 S cm , respectively. The results point to CNPz and DCNPz as promising and
-1
cost-effective building blocks for the development of high-performance n-type polymer semiconductors.
Low crystallinity conjugated polymers have been considered to be potential candidates for OTEs, especially
for flexible devices, since their disordered structure provides an efficient means of introducing dopants and
retains high flexibility innately. Therefore, Gao et al. designed and synthesized two n-type conjugated
polymers, ThDPP-BTz and ThDPP-CNBTz, low crystallinity polymers with dual acceptor backbone
featuring a thiophene-flanked DPP and cyano-substituted benzothiadiazole . Due to its low LUMO
[149]
energy level of below -4.20 eV and low crystallinity, ThDPP-CNBTz achieved high doping efficiency and
better polaron delocalization. After doping with N-DMBI, ThDPP-CNBTz realized high σ of 50.6 S cm and
-1
-2
-1
a PF of 126.8 μW m K at the best, which is among the highest values reported for solution-processed n-
doped polymers. A flexible OTE device also fabricated based on 20 mol% doped polymer; exhibits a
-2
maximum PF of 70 μW m K and excellent bending stability with almost no change in conductivity after
-1
600 cycles. This finding provided a pathway for the development of high-performance n-type materials
suitable for flexible OTE devices.
Recently, Shen et al. made a significant approach to enhance the performance of TE polymer by
incorporation of noncovalently fused-ring strategy. They synthesized pDFSe conjugated polymer using
unique acceptor-triad structure containing DPP and difluorobenzoselenadiazole with noncovalently
fused-ring design, which improves the backbone rigidity . Additionally, an axisymmetric
[150]
thiophene-selenophene-thiophene donor was also incorporated in order to facilitate development of nearly
amorphous microstructures, promoting effective intrachain charge-carrier mobility. The research confirms
that pDFSe is of a close-to-amorphous nature, as supported by XRD and AFM results. XRD reveals a
shorter crystalline correlation length (CCL) of 26.4 Å (~7 layers of π-stacking) for pDFSe compared to 36.3
Å (~10 layers) for more crystalline pDSe. In addition, the paracrystalline disorder parameter (g) of pDFSe is