Structural Insight into Aggregation and Orientation of TPD-Based Conjugated Polymers for Efficient Charge-Transporting Properties
作者:Dae-Hee Lim、Yeon-Ju Kim、Yeong-A Kim、Kyoungtae Hwang、Jong-Jin Park、Dong-Yu Kim
DOI:10.1021/acs.chemmater.8b04605
日期:2019.7.9
In this study, we obtained a new structural insight into the charge-transporting properties in TPD-based polymers that cannot be solely explained in terms of the type of orientation. We synthesized two types of copolymers comprising mono-TPD or bis-TPD as the accepting unit. Although the planarity and energy levels are similar with the mono-TPD unit, the aggregation state is quite different, and the X-aggregation tendency seems to be stronger when the bis-TPD unit is incorporated. In the case of TPD1, an effective π–π orbital overlap is found to originate from the H-aggregates, and 3D charge transport pathways are formed with a bimodal orientation of edge-on and face-on, resulting in an efficient charge transportation (1.84 cm2·V–1·s–1 of hole and 0.31 cm2·V–1·s–1 of electron). In contrast, despite the well-aligned edge-on orientation of TPD2, it exhibited a relatively very low mobility and splitted emission characteristics in photoluminescence spectra because of the tilted intermolecular stacking pattern with an X-shape (0.015 cm2·V–1·s–1 for hole and 0.16 cm2·V–1·s–1 for electron). An overall characterization of the semiconducting polymers was performed, and it was found that the type of aggregation in the final thin films, such as H- or X-aggregation, is indeed important and perhaps more important than the orientation to obtain polymers with a high charge carrier mobility.
在本研究中,我们对基于TPD的聚合物中的电荷传输性质获得了新的结构洞察,这些性质不能仅从取向类型来解释。我们合成了两种类型的共聚物,分别包含单TPD或双TPD作为接受单元。尽管单TPD单元的平面性和能级相似,但其聚集状态有显著差异,且当引入双TPD单元时,X型聚集趋势似乎更强。在TPD1情况下,有效的π-π轨道重叠源自H型聚集,形成了三维电荷传输路径,具有边缘-顶面和顶面-顶面的双峰取向,实现了高效的电荷传输(空穴迁移率为1.84 cm²·V⁻¹·s⁻¹,电子迁移率为0.31 cm²·V⁻¹·s⁻¹)。相比之下,尽管TPD2具有良好的边缘-顶面取向,但由于倾斜的分子间堆积模式呈X形(空穴迁移率为0.015 cm²·V⁻¹·s⁻¹,电子迁移率为0.16 cm²·V⁻¹·s⁻¹),其表现出相对较低的迁移率和光致发光光谱中的分裂发射特性。对半导体聚合物进行了全面的表征,发现最终薄膜中的聚集类型,如H型或X型聚集,确实非常重要,甚至可能比取向更重要,以获得具有高电荷载流子迁移率的聚合物。