Metal screening effect on energy levels at metal/organic interface: Precise determination of screening energy using photoelectron and inverse-photoelectron spectroscopies
Metal screening effect on energy levels at metal/organic interface: Precise determination of screening energy using photoelectron and inverse-photoelectron spectroscopies
复制标题
DOI：
10.1103/physrevb.104.085305
复制
发表时间：
2021-08-11
影响因子：
3.7
通讯作者：
Yoshida, Hiroyuki
中科院分区：
文献类型：
--
作者：
Aihara, Takumi;Abd-Rahman, Syed A.;Yoshida, Hiroyuki
在有机半导体器件中，金属/有机界面处的能级对准极大地影响电极的电荷注入/提取效率。金属表面附近的电荷载流子应通过金属表面的屏蔽效应而稳定，从而导致能隙（最高占据分子轨道（HOMO）-最低未占据分子轨道（LUMO）能隙）变窄并改变金属/有机界面处的能级排列。然而，这种金属屏蔽效应尚未完全阐明，因为一直没有精确的方法来定量评估实验值。本研究利用紫外光电子能谱（UPS）、亚稳原子电子能谱（MAES）和低能逆光电子能谱（LEIPS）研究了苝-3，4，9，10-四羧酸二酐（PTCDA）在Ag（111）和Au（111）原子级平坦金属表面上的准逐层生长膜。通过应用我们最近建立的程序，我们精确地评估了金属屏蔽效应的能量。结果表明，屏蔽效应的金属表面修改的电荷注入/收集势垒在金属/有机界面高达0.25 eV。我们发现，PTCDA的厚度依赖的屏蔽效应是精确地再现的图像电荷模型。
The energy level alignment at the metal/organic interface greatly affects the charge injection/extraction efficiency of electrodes in organic semiconductor devices. The charge carrier in the vicinity of the metal surface should be stabilized by the screening effect of the metal surface, thereby resulting in the narrowing of the energy gap (highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap) and modifying the energy level alignment at the metal/organic interface. However, this metal screening effect has not been fully clarified because there has been no precise way to quantitatively evaluate the experimental values. In this study, we employed ultraviolet photoelectron spectroscopy (UPS), metastable atom electron spectroscopy (MAES), and low-energy inverse photoelectron spectroscopy (LEIPS) to examine the quasi-layer-by-layer grown film of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) on the atomically flat metal surface of Ag(111) and Au(111). By applying a procedure we established recently, we precisely evaluated the energy of the metal screening effect. The results demonstrate that the screening effect of the metal surface modifies the charge injection/collection barrier at the metal/organic interface by as much as 0.25 eV. We found that the PTCDA thickness dependent screening effect is precisely reproduced by the image charge model.