Institut für Physik und Astronomie, Universität Potsdam , Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany.
J Am Chem Soc. 2014 Mar 19;136(11):4245-56. doi: 10.1021/ja4118736. Epub 2014 Mar 11.
We investigated the correlation between the polymer backbone structural regularity and the charge transport properties of poly{[N,N'-bis(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} [P(NDI2OD-T2)], a widely studied semiconducting polymer exhibiting high electron mobility and an unconventional micromorphology. To understand the influence of the chemical structure and crystal packing of conventional regioregular P(NDI2OD-T2) [RR-P(NDI2OD-T2)] on the charge transport, the corresponding regioirregular polymer RI-P(NDI2OD-T2) was synthesized. By combining optical, X-ray, and transmission electron microscopy data, we quantitatively characterized the aggregation, crystallization, and backbone orientation of all of the polymer films, which were then correlated to the electron mobilities in electron-only diodes. By carefully selecting the preparation conditions, we were able to obtain RR-P(NDI2OD-T2) films with similar crystalline structure along the three crystallographic axes but with different orientations of the polymer chains with respect to the substrate surface. RI-P(NDI2OD-T2), though exhibiting a rather similar LUMO structure and energy compared with the regioregular counterpart, displayed a very different packing structure characterized by the formation of ordered stacks along the lamellar direction without detectible π-stacking. Vertical electron mobilities were extracted from the space-charge-limited currents in unipolar devices. We demonstrate the anisotropy of the charge transport along the different crystallographic directions and how the mobility depends on π-stacking but is insensitive to the degree or coherence of lamellar stacking. The comparison between the regioregular and regioirregular polymers also shows how the use of large planar functional groups leads to improved charge transport, with mobilities that are less affected by chemical and structural disorder with respect to classic semicrystalline polymers such as poly(3-hexylthiophene).
我们研究了聚合物主链结构规整性与聚{[N,N'-双(2-辛基十二烷基)-1,4,5,8-萘二酰亚二胺-2,6-二基]-交替-5,5'-(2,2'-联噻吩)}[P(NDI2OD-T2)]电荷输运性质之间的相关性，P(NDI2OD-T2)是一种广泛研究的半导体聚合物，具有高电子迁移率和非常规的微形态。为了了解常规规正聚[N,N'-双(2-辛基十二烷基)-1,4,5,8-萘二酰亚二胺-2,6-二基]-交替-5,5'-(2,2'-联噻吩)][RR-P(NDI2OD-T2)]的化学结构和晶体堆积对电荷输运的影响，我们合成了相应的规不正聚[N,N'-双(2-辛基十二烷基)-1,4,5,8-萘二酰亚二胺-2,6-二基]-交替-5,5'-(2,2'-联噻吩)][RI-P(NDI2OD-T2)]。通过结合光学、X 射线和透射电子显微镜数据，我们对所有聚合物薄膜的聚集、结晶和主链取向进行了定量表征，并将其与电子二极管中的电子迁移率相关联。通过仔细选择制备条件，我们能够获得 RR-P(NDI2OD-T2)薄膜，这些薄膜在三个晶轴上具有相似的结晶结构，但聚合物链相对于基底表面的取向不同。尽管 RI-P(NDI2OD-T2)的 LUMO 结构和能量与规正对应物相当相似，但它表现出非常不同的堆积结构，其特征在于沿层状方向形成有序堆叠，而没有可检测的π堆叠。垂直电子迁移率是从单极器件中的空间电荷限制电流中提取的。我们证明了电荷在不同结晶方向上的各向异性以及迁移率如何取决于π堆叠，但对层状堆积的程度或相干性不敏感。规正和规不正聚合物的比较还表明，使用大的平面官能团如何导致电荷输运的改善，与聚(3-己基噻吩)等经典半晶聚合物相比，迁移率受化学和结构无序的影响较小。
