Voss Matthew G, Challa J Reddy, Scholes D Tyler, Yee Patrick Y, Wu Eric C, Liu Xiao, Park Sanghyun J, León Ruiz Omar, Subramaniyan Selvam, Chen Mengdan, Jenekhe Samson A, Wang Xiaolin, Tolbert Sarah H, Schwartz Benjamin J
Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA, 90095-1569, USA.
Department of Chemical Engineering and Department of Chemistry, University of Washington, Seattle, WA, 98195-1750, USA.
Adv Mater. 2021 Jan;33(3):e2000228. doi: 10.1002/adma.202000228. Epub 2020 Dec 9.
Molecular dopants are often added to semiconducting polymers to improve electrical conductivity. However, the use of such dopants does not always produce mobile charge carriers. In this work, ultrafast spectroscopy is used to explore the nature of the carriers created following doping of conjugated push-pull polymers with both F TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) and FeCl . It is shown that for one particular push-pull material, the charge carriers created by doping are entirely non-conductive bipolarons and not single polarons, and that transient absorption spectroscopy following excitation in the infrared can readily distinguish the two types of charge carriers. Based on density functional theory calculations and experiments on multiple push-pull conjugated polymers, it is argued that the size of the donor push units determines the relative stabilities of polarons and bipolarons, with larger donor units stabilizing the bipolarons by providing more area for two charges to co-reside.
分子掺杂剂通常被添加到半导体聚合物中以提高电导率。然而，使用此类掺杂剂并不总是能产生移动电荷载流子。在这项工作中，超快光谱被用于探究用F TCNQ（2,3,5,6 - 四氟 - 7,7,8,8 - 四氰基对苯二醌二甲烷）和FeCl对共轭推挽聚合物进行掺杂后所产生的载流子的性质。结果表明，对于一种特定的推挽材料，掺杂产生的电荷载流子完全是不导电的双极化子而非单极化子，并且在红外激发后的瞬态吸收光谱能够很容易地区分这两种类型的电荷载流子。基于密度泛函理论计算以及对多种推挽共轭聚合物的实验，有人认为供体推单元的大小决定了极化子和双极化子的相对稳定性，较大的供体单元通过为两个电荷提供更多共居面积来稳定双极化子。
