Polymorphism controls the degree of charge transfer in a molecularly doped semiconducting polymer
Polymorphism controls the degree of charge transfer in a molecularly doped semiconducting polymer
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DOI：
10.1039/c8mh00223a
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发表时间：
2018-07-01
影响因子：
13.3
通讯作者：
Moule, Adam J.
中科院分区：
文献类型：
--
作者：
Jacobs, Ian E.;Cendra, Camila;Moule, Adam J.
当有机半导体（OSC）与可以充当p型掺杂剂的电子受体分子共混时，理想地应该存在电荷从OSC到掺杂剂的完全（整数）转移。然而，一些掺杂剂-OSC共混物反而形成电荷转移复合物（CTC），其特征在于两个分子之间的部分电荷转移（CT）和强轨道杂化。分数CT掺杂不能有效地产生自由电荷载流子，但尚不清楚什么条件导致不完全电荷转移。在这里，我们表明，通过改变薄膜的处理条件，在掺杂剂-掺杂剂对聚（3-己基噻吩）：2，3，5，6四氟-7，7，8，8-四氰基醌二甲烷（P3 HT：F4 TCNQ），我们可以选择性地获得近纯的整数或分数CT相。分数阶CT薄膜的电导率比相应的整数阶CT薄膜低约2个数量级，并且光学吸收光谱显著不同。掠入射广角X射线衍射（GIXD）表明，分数CT电影显示出异常致密和有序的晶体结构。这些薄膜表现出较低的paracrysticity和较短的层状和p-堆叠的距离比未掺杂的薄膜在类似的条件下处理。使用平面波DFT，我们得到的结构与GIXD所观察到的密切匹配的晶胞参数。在单一OSC掺杂剂系统中首次观察到分数和整数CT，证明了结构效应对OSC掺杂的重要性，并为进一步研究打开了大门。
When an organic semiconductor (OSC) is blended with an electron acceptor molecule that can act as a p-type dopant, there should ideally be complete (integer) transfer of charge from the OSC to the dopant. However, some dopant-OSC blends instead form charge transfer complexes (CTCs), characterized by fractional charge transfer (CT) and strong orbital hybridization between the two molecules. Fractional CT doping does not efficiently generate free charge carriers, but it is unclear what conditions lead to incomplete charge transfer. Here we show that by modifying film processing conditions in the semiconductor-dopant couple poly(3-hexylthiophene): 2,3,5,6tetrafluoro- 7,7,8,8,-tetracyanoquinodimethane (P3HT: F4TCNQ), we can selectively obtain nearly pure integer or fractional CT phases. Fractional CT films show electrical conductivities approximately 2 orders of magnitude lower than corresponding integer CT films, and remarkably different optical absorption spectra. Grazing incidence wide-angle X-ray diffraction (GIXD) reveals that fractional CT films display an unusually dense and well-ordered crystal structure. These films show lower paracrystallinity and shorter lamellar and p-stacking distances than undoped films processed under similar conditions. Using plane-wave DFT we obtain a structure with unit cell parameters closely matching those observed by GIXD. This first-ever observation of both fractional and integer CT in a single OSC-dopant system demonstrates the importance of structural effects on OSC doping and opens the door to further studies.