Orientation-dependent ionization energies and interface dipoles in ordered molecular assemblies
Orientation-dependent ionization energies and interface dipoles in ordered molecular assemblies
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DOI：
10.1038/nmat2119
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发表时间：
2008-03-01
期刊：
影响因子：
41.2
通讯作者：
Koch, Norbert
中科院分区：
文献类型：
--
作者：
Duhm, Steffen;Heimel, Georg;Koch, Norbert
虽然一个孤立的单个分子显然只有一个电离电位，但在有序的分子组合中发现了多个电离电位。金属衬底上典型π共轭有机化合物的光电子能谱结合第一性原理计算和静电模型揭示了分子层表面偶极子的存在。在概念上不同于金属表面的表面偶极子，它的起源在于分子电子结构的细节，它的大小取决于分子相对于有序组装表面的取向。在随后生长的薄膜中，适当的基底预图图化以诱导特定的分子取向，从而允许通过控制单层形态来调节一种分子的电离电位，最高可达0.6 eV。除了提供对这一现象的深入理解外，我们的研究还为改进有机-有机异质结、空穴或电子阻挡层以及减少有机电子器件中载流子注入障碍提供了设计指导。
Although an isolated individual molecule clearly has only one ionization potential, multiple values are found for molecules in ordered assemblies. Photoelectron spectroscopy of archetypical pi-conjugated organic compounds on metal substrates combined with first-principles calculations and electrostatic modelling reveal the existence of a surface dipole built into molecular layers. Conceptually different from the surface dipole at metal surfaces, its origin lies in details of the molecular electronic structure and its magnitude depends on the orientation of molecules relative to the surface of an ordered assembly. Suitable pre-patterning of substrates to induce specific molecular orientations in subsequently grown films thus permits adjusting the ionization potential of one molecular species over up to 0.6 eV via control over monolayer morphology. In addition to providing in-depth understanding of this phenomenon, our study offers design guidelines for improved organic-organic heterojunctions, hole- or electron-blocking layers and reduced barriers for charge-carrier injection in organic electronic devices.