Electrostatic Interactions Shape Molecular Organization and Electronic Structure of Organic Semiconductor Blends
Electrostatic Interactions Shape Molecular Organization and Electronic Structure of Organic Semiconductor Blends
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DOI：
10.1021/acs.chemmater.9b04763
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发表时间：
2020-02-11
影响因子：
8.6
通讯作者：
Salzmann, Ingo
中科院分区：
文献类型：
--
作者：
D'Avino, Gabriele;Duhm, Steffen;Salzmann, Ingo
共轭分子的卤化是一种通过诱导效应和长程分子间静电相互作用来调节分子薄膜电子结构的有效方法。卤化分子与其原始对应物的混合最近被证明成功地改变了混合物的能级，以通过混合比来调节有机太阳能电池的开路电压。在这里，我们表明，这种效果的普遍理由是不同样有效的不同的分子取向。我们提供了一个全面的实验和理论分析的原型共混物形成的并五苯和全氟并五苯与电子性质的结构。我们发现了一个混合堆叠结构的基序，在站立和躺着的方向取决于基板的性质。在站立的方向上，电离势位于纯组分的值之间，与建立的平均分子四极矩的图像一致。然而，对于躺着的方向，我们在实验中观察到电离势低于两个原始值，这似乎与这个简单的理由不一致。静电模拟的基础上的知识的原子结构的薄膜捕获的复杂的实验方案的两个方向。特别是，超低电离电位的薄膜形成的说谎分子被确定为一个签名的单层结构，其中四极相互作用是负责的差异ca。0.4 eV的最高占据分子轨道能量相比，具有相同的分子取向的较厚的膜。
Halogenation of conjugated molecules represents a powerful approach to tune the electronic structure of molecular thin films through inductive effects and long-range intermolecular electrostatic interactions. The mixing of halogenated molecules with their pristine counterparts has recently proven successful in altering the blend's energy levels to adjust the open-circuit voltage of organic solar cells by the mixing ratio. Here, we show that the prevailing rationale for this effect is not equally valid for different molecular orientations. We provide a comprehensive experimental and theoretical analysis of the prototypical blend formed by pentacene and perfluoropentacene to relate structure with electronic properties. We find a mixed-stack structural motif in standing and lying orientations depending on the substrate nature. In the standing orientation, the ionization potential lies in between the values of the pure components, in line with the established picture of averaged molecular quadrupole moments. For the lying orientation, however, we experimentally observe an ionization potential lower than both pristine values, which seems at odds with this simple rationale. Electrostatic simulations based on the knowledge of the atomistic structure of the films capture the complex experimental scenario for both orientations. In particular, the ultralow ionization potential of films formed by lying molecules is identified as a signature of the monolayer structure, where quadrupolar interactions are responsible for a difference of ca. 0.4 eV in the highest occupied molecular orbital energy as compared to thicker films with the same molecular orientation.