有机发光器件界面与器件稳定性的研究

【作者】 谢作提；

【导师】 侯晓远； 丁训民；

【作者基本信息】 复旦大学 ， 凝聚态物理， 2008， 博士

【摘要】 随着有机半导体工业的飞速发展,人们对有机功能器件中基础物理、化学问题的研究越来越深入。在以有机光发射二极管（OLED）、有机场效应晶体管（OFET）及有机光伏电池（OPVC）等典型多层膜结构器件中,提高界面载流了注入效率以及器件寿命一直是人们努力的重点。界面载流子的注入效率最主要的是受注入势垒的影响。在Schottky-Mott模型下,金属/有机界面电子（空穴）注入势垒取决于金属费米能级到LUMO（HOMO）的能量大小,但实际的多数金属/有机界面和部分有机/有机界面,由于界面偶极子的存在而偏离该模型。因此,研究有机半导体界面的电子能级结构和界面偶极子对有机光电器件的优化具有基础指导意义。光电子能谱技术（UPS/XPS）已经被证实是研究有机半导体表面与界面能级排列及界面化学的一种行之有效的实验方法。本文利用同步辐射光电子能谱技术,在超高真空环境中采取分步沉积的原位薄膜制备方法,对有机/金属界面的形成过程与电子结构进行了大量的研究。另外,在有机发光器件的恒压特性和器件空穴传输控制方面也进行了研究。具体如下:1、我们利用高分辨同步辐射光电子能谱,仔细研究了LiF/Al/Alq₃、Al＼LiF和LiF＼Al界面的电子结构特性。清楚地看到在Al/LiF界面的电子转移过程,为LiF作为缓冲层在Al/Alq₃器件界面的化学反应机制提供了直接的实验证据。2、我们对C₆0修饰过的Al金属表面进行同步辐射光电子能谱研究,仔细测量分析了Al＼C₆₀和Al＼C₆₀＼NPB界面的价带,观察到了C₆₀修饰的Al金属表面功函数提高,以及C₆₀的插入导致Al＼NPB界面空穴注入势垒从1.55eV降低到0.57eV的价带信息。3、我们研究了典型OLEDs（ITO＼NPB＼Alq＼LiF＼Al）的恒压工作特性,对器件在恒压开启之时的稳定性进行了探讨。另外,我们将电离性质不同的金属如Li,Al,Ag和Au与NPB进行掺杂,分析金属有机掺杂体系对空穴传输阻挡作用,并认为金属掺杂对空穴的阻挡与他们的电离性有关。我们在电子传输层中,利用金属掺杂对空穴的阻挡作用来降低器件的漏电流,可以有效地提高器件的稳定性。更多还原

【Abstract】 With up-growing development in the organic semiconductor industry,more and more insights have been put into the fundamental physics and chemistry about the operations of the organic microelectronic devices.In those typical layer-based organic devices,including organic light-emitting diode（OLED）,organic field effect transistor（OFET） and organic photovoltaic cell （OPVC）,the most focused work are to improve the injection efficiency through the interfaces and the lifetime of the devices.Mostly,the major factor to control carrier injection is the interface barrier height.At metal/organic semiconductor interface,the electron（hole） injection barrier depends on the position of the LUMO（HOMO） with respect to the metal Fermi level under the Schottky-Mott rule.Most of the actual metal/organic or some of the organic/organic interfaces, however,deviate from the rule due to the existence of interface dipoles.Therefore,the studies of energy level alignment and dipoles at organic interfaces would play a key role on the optimization of organic electronic devices,it has been demonstrated that photoemission（UPS/XPS） is one of the most successful experimental methods to research the interface energy alignment and chemistry.In this thesis,a series of interfaces,including organic/metal,organic/organic and organic/inorganic semiconductors,were investigated systematically to elucidate the interface formations and electronic structures by synchrotron radiation photoemission（SRPES） method.All the molecules or metal atoms were deposited step-wised in situ onto substrate under ultra high vacuum system.In addition,we also study the feature of the device operated at constant voltage and control the transportation of hole of the OLEDs.The detail subject and results are showed as below:1 We have employed the high-resolution synchrotron radiation photoemission to investigate the electronic structure of the interfaces of LiF/AI/Alq,AI/LiF and LiF/Al,the detailed process and product of the reaction between LiF and Al was investigated clearly.The chemical reaction model of the role of LiF at Al/Alq interface was well demonstrated. 2 The synchrotron radiation photoemission spectroscopy study showed that the energy level of the interface between the hole transport material NPB and Al could be varied by adjusting the thickness of pre-coved C₆₀ on the metal substrate.The interface dipole induced shifts of the highest occupied molecular orbital（HOMO） level and the cut-off of the NPB layer by inserting thin C₆₀ layer were investigated and lower the barrier height for hole injecting from Al to NPB by as much as 0.98eV.The optimize thickness of the inserted C₆₀ layer was found to be 8-12（?） which could increase the work function of the Al from 4.22eV to 4.92eV.3 We have studied the turn-on stability of aging OLEDs by constant voltage measurement.The characteristics of OLEDs which operated by constant voltage was discussed.In addition,we have studied the different hole block effect of different metal（Au、Ag、Al、Li） doped into hole transport layer NPB.We proposed that the hole blocking ability depends on the metal’s ionizability. Transient photo-voltage spectra shows the different injection ability of holes of different ITO\NPB:metal interfaces.Utility of the hole blocking effect of the metal doped system in the electron transport layer to reduced the leakage of holes across the Alq layer to the cathode and gained the more stability than the device that without this layer.更多还原