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Shen et al. Soft Sci 2023;3:20 https://dx.doi.org/10.20517/ss.2023.10 Page 3 of 14
(PEDOT:PSS) can be prepared using a commercially available material and a simple dilution filtration
[34]
method . Li et al. have successfully obtained PEDOT:PSS thin films with a power factor (PF) as high as 133
-2
-1
μW·m ·K using this method . Since the discovery of classic conductive polymers, π-conjugated polymers
[35]
have been a focus of attention in various organic electronic device fields due to their convenient structural
modification and the close relationship between their structure and properties. However, modifying π-
conjugated polymers often involves developing larger π-conjugated planar systems, which requires
consideration of the poorer solution processability and film-forming performance caused by the
introduction of large rigid structures. Hence, researchers must continue to explore a straightforward,
dependable, and practical approach for producing polymer films from precursors with high rigidity
structures. This requires continuous research and comprehension of the correlation between polymer
molecular structure and performance, along with persistent exploration of advanced material preparation
technology. As a result, the dimensionless figure of merit (ZT) value of organic TE materials has
significantly expanded. However, earlier studies failed to consider the impact of microstructural aggregation
state of polymer molecules on TE performance, leading to fragmented understanding of the relationship
between polymer structure, properties, and microstructural aggregation state. Due to this lack of clarity,
organic TE materials are currently unable to achieve large-scale commercial applications.

We have synthesized three monomers, according to the H NMR spectra in Supplementary Figures 1-3,
1
namely 2,2',3,3'-tetrahydro-5,5'-bithieno[3,4-b][1,4] dioxine (BED), 2,5-bis(2,3-dihydrothieno [3,4-
b][1,4]dioxin-5-yl)thiophene (BED-T), and 2,5-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl) thieno[3,2-b]
thiophene (BED-TT) by integrating the building units Th and TT into the EDOT block. The detailed
synthesis procedures are presented in the Supplementary experimental section. We investigated the effects
of changing the backbone conjugated structure of precursors on the preparation of polymer films,
morphology, band gap, and TE performance. Our findings suggest that the introduction of Th units
expands the conjugate plane of precursor molecules, which effectively promotes the ordered stacking of
polymer molecules. This leads to decoupling between the σ and S, ultimately significantly improving the TE
properties of the material.

RESULTS AND DISCUSSION
As our understanding of the relationship between structure and performance continues to advance, the
synthesis of low-solubility, highly rigid polymers are becoming increasingly prevalent. However, this has
presented a significant challenge in terms of film formation during polymer preparation, and conventional
methods may not be sufficient to achieve high-quality polymer films. The rigidity of BEDs molecules
[Supplementary Scheme 1] further complicates this task, making it even more difficult to obtain high-
quality polymer films [36,37] .To overcome the film quality problem for conjugated polymers, we propose a
novel method for preparing high-quality films using the spray-spin coating method for polymerization , as
[38]
illustrated in Figure 1. In this method, the monomer solution is atomized by an extremely fine atomizer and
uniformly deposited on a substrate coated with a thin film of oxidizing agent. The monomer solution
immediately reacts with the oxidizing agent, and high-quality polymer films are obtained after ethanol
rinsing. Detailed film preparation steps are presented in the polymerization of BEDs monomers and
polymer films preparation section of the Supplementary Material. By using a precursor with a large π-
conjugate structure, we are able to achieve high-quality polymer preparation through a simple and low-cost
solution treatment method. This opens potential applications in the field of photoelectricity.

To determine the coupling mode during precursor polymerization, we conducted Fourier transform
infrared (FTIR) spectroscopy on the PBEDs films [Here, we define PBEDs as a group of polymer PBED,
P(BED-T) and P(BED-TT)]. Supplementary Figure 4 shows that there are hardly any absorption peaks near
3,000-3,100 cm (which were not depicted in the graph), corresponding to the C-H bond vibration at the 2
-1

1

H

NMR

spectra

in

Supplementary Figures 1-3

,

namely

2,2',3,3'-tetrahydro-5,5'-bithieno[3,4-b][1,4]

dioxine

(BED),

2,5-bis(2,3-dihydrothieno

[3,4-

b][1,4]dioxin-5-yl)thiophene

(BED-T),

and

2,5-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)

thieno[3,2-b]

thiophene

(BED-TT)

by

integrating

the

building

units

Th

and

TT

into

the

EDOT

block.

The

detailed

synthesis

procedures

are

presented

in

the

Supplementary

experimental

section.

We

investigated

the

effects

of

changing

the

backbone

conjugated

structure

of

precursors

on

the

preparation

of

polymer

films,

morphology,

band

gap,

and

TE

performance.

Our

findings

suggest

that

the

introduction

of

Th

units

expands

the

conjugate

plane

of

precursor

molecules,

which

effectively

promotes

the

ordered

stacking

of

polymer

molecules.

This

leads

to

decoupling

between

the

σ

and

S

,

ultimately

significantly

improving

the

TE

properties of the material.