Park Sang-Geon, Mori Tatsuo
Division of Smart Electrical and Electronic Engineering, Silla University 46958, Korea.
Department of Electrical Engineering and Computer Science, Nagoya University, 464-8601, Japan.
J Nanosci Nanotechnol. 2018 Sep 1;18(9):6010-6013. doi: 10.1166/jnn.2018.15575.
In this study, we investigated the photoelectric effect and optimization of an organic light-emitting diode (OLED) depending on the presence or absence of a fluorinated self-assembled monolayer (FLSAM) and by varying the thickness of N,N'-Di (1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (α-NPD) from 0 nm to 50 nm. The large distinction in electronegativity between the carbon and the fluorine replacing hydrogen in the alkyl chain of FLSAM generates a strong dipole moment to elevate the vacuum level, resulting in a change of the work function. This eliminates the injection barrier between the work function of the ITO modified by FLSAM and the highest occupied molecular orbital (HOMO) level of the hole-transport layer, thus leading to excellent driving voltage characteristics. Devices without FLSAM had a driving voltage more than twice that of devices using with FLSAM. The introduction of α-NPD as the hole-transport layer enhanced the electrical conductivity by facilitating the transport of holes. However, due to the inherent insulating film properties of α-NPD, the increase in its thickness resulted in a decrease in current density.
在本研究中，我们研究了基于含氟自组装单分子层（FLSAM）的有无以及通过将N，N'-二（1-萘基）-N，N'-二苯基-（1，1'-联苯）-4，4'-二胺（α-NPD）的厚度从0纳米变化到50纳米时有机发光二极管（OLED）的光电效应及优化情况。FLSAM烷基链中取代氢的碳和氟之间的电负性存在很大差异，产生了很强的偶极矩以提高真空能级，从而导致功函数发生变化。这消除了经FLSAM修饰的氧化铟锡（ITO）的功函数与空穴传输层的最高占据分子轨道（HOMO）能级之间的注入势垒，进而带来优异的驱动电压特性。没有FLSAM的器件的驱动电压是使用FLSAM的器件的两倍多。引入α-NPD作为空穴传输层通过促进空穴传输增强了导电性。然而，由于α-NPD固有的绝缘膜特性，其厚度增加导致电流密度降低。
