共轭体系中多尺度电荷输运的高分子物理
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本文是由Gu和Loo等人在2019年发表于《聚合物科学杂志B部分：聚合物物理学》的一篇研究论文，标题为“共轭系统中多尺度电荷传输的聚合物物理”。该研究主要关注的是在共轭聚合物中的电荷传输现象，这是一个在材料科学、电子学和光电子学领域非常重要的主题，特别是对于开发高性能的有机电子器件，如有机太阳能电池、有机场效应晶体管等。
电荷运输是共轭聚合物的核心特性之一，它决定了这些材料在电子设备中的应用潜力。共轭聚合物，因其独特的电子结构，具有良好的电荷载流子迁移能力。在多尺度电荷传输的研究中，作者可能探讨了从分子到宏观不同层次上的电荷移动机制，包括电子或空穴在单个分子间的跳跃、在纳米尺度的聚集态结构中的扩散以及在微米级别的宏观薄膜中的输运。
文章可能涵盖了以下几个关键知识点：
1. **共轭体系与电荷传输**：共轭聚合物的π电子系统允许电子在多个碳原子之间自由移动，形成离域π键，这种结构使得电荷可以在聚合物链上有效地传输。
2. **多尺度理解**：研究可能涉及了从原子级的电子结构到聚合物薄膜的宏观性能的多层次分析，揭示了电荷传输的复杂性，包括分子排列、结晶度、缺陷状态以及界面性质等因素的影响。
3. **电荷载流子的产生和捕获**：在共轭聚合物中，电荷载流子（电子和空穴）的产生和捕获过程对器件性能至关重要。作者可能讨论了光照、电场或其他激励方式如何影响这些过程。
4. **聚合物的聚集态结构**：聚合物的聚集态结构，如晶区和非晶区的存在，会显著影响电荷的扩散和迁移率。研究可能分析了不同结构对电荷传输效率的贡献。
5. **实验方法与表征技术**：为了研究电荷传输，作者可能采用了多种实验技术，如电荷注入和提取实验、光谱学（如吸收光谱、荧光光谱、拉曼光谱等）、电化学测量以及电子显微镜等。
6. **理论模拟与计算**：除了实验数据，理论模拟也可能被用来解释和预测电荷在共轭聚合物中的行为，例如使用密度泛函理论（DFT）和分子动力学模拟。
7. **器件性能与优化**：最后，研究可能讨论了如何通过调整聚合物的设计、合成条件和加工方法来优化电荷传输性能，以提升有机电子器件的性能。
由于原始文件的具体内容未给出，以上分析基于标题和描述中的信息进行推测。实际论文可能详细阐述了这些概念，并提供了实验数据和详细的分析结果。对于想要深入了解共轭聚合物电荷传输特性的读者，这篇论文将是一个宝贵的资源。
microstructural origin for mechanical and electrical properties.
17
For example, moderately crystalline P3HT is more flexible and
ductile than highly crystalline PBTTT. The field-effect mobility
ratio of transistors comprising these two polymers is very simi-
lar to their elastic modulus ratio, shown in Figure 1.
18
In light
of the success in engineering desired mechanical properties of
polyolefins, we believe that many opportunities exist not only to
establish empirical correlations between mechanical and electri-
cal properties, like the mobility–modulus relationship men-
tioned above, but also to shed light on the underlying structural
origin and polymer physics for charge transport.
17
This review
highlights how these ideas and frameworks have been
leveraged—and in some other cases extended—to gain insights
on how polymer microstructure impacts charge transport in
conjugated polymers. For instance, long polymer chains have
the ability of bridging adjacent crystallites; such chains are
known as polymer tie chains. The presence of tie chains
strongly influences the resistance to slow crack growth in poly-
ethylene resins.
19,20
By extension, the presence of tie chains that
connect neighboring crystallites has been recently shown to also
play a critical role on charge transport in P3HT. Although direct
visualization of tie chains remains challenging, this extension
allows estimation of tie-chain fraction in P3HT, establishing the
concept of a critical threshold of tie-chain connectivity that is
required for macroscopic charge transport in P3HT.
21
In this review, we aim to assess the polymer physics of multi-
scale charge transport in conjugated systems. We first describe
the microstructural features of conjugated polymers across mul-
tiple length scales that can influence charge transport. We then
assess a plethora of literature that has examined the structure–
electrical property relationships of conjugated polymers,
highlighting both empirical and theoretical studies aimed at
identifying the governing molecular characteristics and struc-
tural features for charge transport. We seek to draw insights
from these collective studies to understand the underlying
charge-transport mechanisms in such complex systems and pro-
pose design rules accordingly. Although there exist transistors
comprising many other more exotic polymers whose mobilities
are higher than those of P3HT transistors, the abundance of
literature on this model polymer system allows for a more in-
depth analysis of structure–property relationships. Many impor-
tant physical parameters, which are not available for most other
conjugated polymers, have been characteri zed for P3HT, includ-
ing its persistence length (3 nm),
22
monomer length
(0.39 nm),
23
equilibrium melting temperature (272
C),
24,25
and
enthalpy of fusion of a perfect crystal (49 J g
−1
),
25
and so on. As
a result, much of our discussion will be focused on P3HT. None-
theless, we point out differences between P3HT and other con-
jugated polymers where appropriate. Finally, we discuss
materials design rules and processing guidelines that have sur-
faced from these collective works for improving charge trans-
port and propose opportunities for further progress. This
review focuses on charge transport in homopolymers. We refer
the readers to other reviews for a comprehensive discussion of
polymer blends and block copolymers explored for their
FIGURE 1 Comparison of the field effect mobility and elastic
modulus of P3HT, as-cast pBTTT (pBTTT-AC), and annealed
pBTTT (pBTTT-AN) films. Inset, the mobility and elastic modulus
of a semicrystalline polymer with increasing percent
crystallinity, based on composite theories of charge transport
and elastic modulus with two distinct values for the amorphous
(μ
M
, E
M
) and crystalline (μ
C
, E
C
) portions of the films. Reprinted
with permission from (ACS Nano 2010, 4, 7538–7544). Copyright
(2010) American Chemical Society.
Kaichen Gu received his B.A. and M.Eng. in Chemical Engineering from the University of
Cambridge in 2015. He is currently a Ph.D. candidate, advised by Prof. Yueh-Lin Loo, in the
Department of Chemical and Biological Engineering at Princeton University. His research
work focuses on the elucidation of charge-transport mechanisms in semiconducting conju-
gated polymer thin films.
Yueh-Lin Loo is the Theodora D. ’78 and Willliam H. Walton III ’74 Professor in Engineering
and director of the Andlinger Center for Energy and the Environment at Princeton Univer-
sity. Her group is interested in the processing and structural development of materials for
lightweight and flexible solar cells and circuits, the combination is explored for self-powered
“smart” windows to increase occupant comfort, building and energy efficiencies. She is a
Fellow of the American Physical Society.
JOURNAL OF POLYMER SCIENCE, PART B: POLYMER PHYSICS 20192
JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERPHYSICS.ORGREVIEW
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