Crispin Xavier, Geskin Victor, Crispin Annica, Cornil Jérôme, Lazzaroni Roberto, Salaneck William R, Brédas Jean-Luc
Department of Physics and Measurement Technology, Linköping University, S-58183 Linköping, Sweden.
J Am Chem Soc. 2002 Jul 10;124(27):8131-41. doi: 10.1021/ja025673r.
In organics-based (opto)electronic devices, the interface dipoles formed at the organic/metal interfaces play a key role in determining the barrier for charge (hole or electron) injection between the metal electrodes and the active organic layers. The origin of this dipole is rationalized here from the results of a joint experimental and theoretical study based on the interaction between acrylonitrile, a pi-conjugated molecule, and transition metal surfaces (Cu, Ni, and Fe). The adsorption of acrylonitrile on these surfaces is investigated experimentally by photoelectron spectroscopies, while quantum mechanical methods based on density functional theory are used to study the systems theoretically. It appears that the interface dipole formed at an organic/metal interface can be divided into two contributions: (i) the first corresponds to the "chemical" dipole induced by a partial charge transfer between the organic layers and the metal upon chemisorption of the organic molecules on the metal surface, and (ii) the second relates to the change in metal surface dipole because of the modification of the metal electron density tail that is induced by the presence of the adsorbed organic molecules. Our analysis shows that the charge injection barrier in devices can be tuned by modulating various parameters: the chemical potential of the bare metal (given by its work function), the metal surface dipole, and the ionization potential and electron affinity of the organic layer.
在基于有机物的（光）电子器件中，有机/金属界面处形成的界面偶极子在决定金属电极与活性有机层之间电荷（空穴或电子）注入势垒方面起着关键作用。本文根据一项基于π共轭分子丙烯腈与过渡金属表面（铜、镍和铁）之间相互作用的联合实验和理论研究结果，对这种偶极子的起源进行了合理的解释。通过光电子能谱对丙烯腈在这些表面上的吸附进行了实验研究，同时采用基于密度泛函理论的量子力学方法对这些体系进行了理论研究。结果表明，在有机/金属界面处形成的界面偶极子可分为两个部分：（i）第一部分对应于有机分子化学吸附在金属表面时，有机层与金属之间通过部分电荷转移诱导产生的“化学”偶极子；（ii）第二部分与由于吸附的有机分子的存在而导致的金属电子密度尾部变化所引起的金属表面偶极子变化有关。我们的分析表明，器件中的电荷注入势垒可通过调节各种参数来调整：裸金属的化学势（由其功函数给出）、金属表面偶极子以及有机层的电离势和电子亲和势。
