Organic field-effect transistors (OFETs) are considered almost purely interfacial devices with charge current mainly confined in the first two semiconducting layers in contact with the dielectric with no active role of the film thickness exceeding six to eight monolayers (MLs). By a combined electronic, morphological, structural, and theoretical investigation, it is demonstrated that the charge mobility and source–drain current in 2,20-(2,20-bithiophene-5,50-diyl)bis(5-butyl-5H-thieno[2,3-c]pyrrole-4,6)-dione (NT4N) organic transistors directly correlate with the out-of-plane domain size and crystallite orientation in the vertical direction, well beyond the dielectric interfacial layers. Polycrystalline films with thickness as high as 75 nm (≈30 MLs) and 3D molecular architecture provide the best electrical and optoelectronic OFET characteristics, highlighting that the molecular orientational order in the bulk of the film is the key-enabling factor for optimum device performance. X-ray scattering analysis and multiscale simulations reveal the functional correlation between the thickness-dependent molecular packing, electron mobility, and vertical charge distribution. These results call for a broader view of the fundamental mechanisms that govern field-effect charge transport in OFETs beyond the interfacial 2D paradigm and demonstrate the unexpected role of the out-of-plane domain size and crystallite orientation in polycrystalline films to achieve optimum electronic and optoelectronic properties in organic transistors.

中文翻译：

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超越分子薄膜晶体管中的二维场效应电荷传输范例

有机场效应晶体管 (OFET) 被认为几乎是纯界面器件，其充电电流主要限制在与电介质接触的前两个半导体层中，膜厚度超过六到八个单层 (ML) 时没有任何积极作用。通过结合电子学、形态学、结构和理论研究，证明了 2,20-(2,20-bithiophene-5,50-diyl)bis(5-butyl-5) 中的电荷迁移率和源漏电流H -噻吩并[2,3- c]pyrrole-4,6)-dione (NT4N) 有机晶体管与面外畴尺寸和垂直方向的微晶取向直接相关，远远超出介电界面层。厚度高达 75 nm（≈30 MLs）和 3D 分子结构的多晶薄膜提供了最佳的电气和光电 OFET 特性，突出表明薄膜主体中的分子取向顺序是实现最佳器件性能的关键因素。X 射线散射分析和多尺度模拟揭示了厚度相关的分子堆积、电子迁移率和垂直电荷分布之间的函数关系。