Yang Yongfan, Silva de Moraes Lygia, Ruzié Christian, Schweicher Guillaume, Geerts Yves Henri, Kennedy Alan R, Zhou Hengyu, Whittaker St John, Lee Stephanie S, Kahr Bart, Shtukenberg Alexander G
Department of Chemistry and Molecular Design Institute, New York University, New York, NY, 10003, USA.
Laboratoire de Chimie des Polymères, Faculté des Sciences, Université Libre de Bruxelles (ULB), Boulevard du Triomphe, CP 206/01, Brussel, 1050, Belgium.
Adv Mater. 2022 Sep;34(38):e2203842. doi: 10.1002/adma.202203842. Epub 2022 Aug 19.
Many molecular crystals (approximately one third) grow as twisted, helicoidal ribbons from the melt, and this preponderance is even higher in restricted classes of materials, for instance, charge-transfer complexes. Previously, twisted crystallites of such complexes present an increase in carrier mobilities. Here, the effect of twisting on charge mobility is better analyzed for a monocomponent organic semiconductor, 2,5-bis(3-dodecyl-2-thienyl)-thiazolo[5,4-d]thiazole (BDT), that forms twisted crystals with varied helicoidal pitches and makes possible a correlation of twist strength with carrier mobility. Films are analyzed by X-ray scattering and Mueller matrix polarimetry to characterize the microscale organization of the polycrystalline ensembles. Carrier mobilities of organic field-effect transistors are five times higher when the crystals are grown with the smallest pitches (most twisted), compared to those with the largest pitches, along the fiber elongation direction. A tenfold increase is observed along the perpendicular direction. Simulation of electrical potential based on scanning electron microscopy images and density functional theory suggests that the twisting-enhanced mobility is mainly controlled by the fiber organization in the film. A greater number of tightly packed twisted fibers separated by numerous smaller gaps permit better charge transport over the film surface compared to fewer big crystallites separated by larger gaps.
许多分子晶体（约三分之一）从熔体中生长为扭曲的螺旋带状物，在特定类型的材料中，这种情况更为常见，例如电荷转移复合物。此前，此类复合物的扭曲微晶会使载流子迁移率增加。在此，针对单组分有机半导体2,5-双（3-十二烷基-2-噻吩基）-噻唑并[5,4-d]噻唑（BDT），能更好地分析扭曲对电荷迁移率的影响。BDT会形成具有不同螺旋间距的扭曲晶体，从而能够将扭曲强度与载流子迁移率关联起来。通过X射线散射和穆勒矩阵偏振测量法对薄膜进行分析，以表征多晶集合体的微观组织。与沿纤维伸长方向具有最大间距（扭曲程度最小）的晶体相比，当晶体以最小间距（扭曲程度最大）生长时，有机场效应晶体管的载流子迁移率高出五倍。在垂直方向上观察到载流子迁移率提高了十倍。基于扫描电子显微镜图像和密度泛函理论对电势进行的模拟表明，扭曲增强的迁移率主要受薄膜中纤维组织的控制。与由较大间隙分隔的较少大晶粒相比，由大量较小间隙分隔的大量紧密堆积的扭曲纤维能使电荷在薄膜表面更好地传输。
