【作者】 张福俊；

【导师】 徐叙瑢；

【作者基本信息】 北京交通大学 ， 光学， 2007， 博士

【摘要】 本论文主要研究了提高固态阴极射线发光亮度的几种途径，并针对界面问题利用紫外光电子谱研究了有机／有机材料界面的能级结构，利用原子力显微镜研究了有机分子在不同的衬底上的表面形貌。针对提高固态阴极射线发光亮度的工作是从上游、本身、下游三个方面深入的。上游的工作主要包括两部分：初电子来源和选择电子加速能力强的材料。从瞬态光谱上通过比较四种电致发光器件的正负半周期的亮度的变化，证明了分层优化发光中初电子的来源主要是从电极的隧穿。从瞬态光谱中比较了正负半周期内最大亮度的变化，证明了SiO₂的电子加速能力比ZnS的电子加速能力强。本身的工作主要是从影响发光的内在因素开展的。在固态阴极射线发光中找到了场致发光中分子理论与能带理论适用的条件，它们的分水岭是激子的场离化。激子场离化之前是激子发光，符合分子理论。激子场离化之后出现辐射复合发光，符合能带理论。考虑到有机电致发光中激子的发光寿命在ns量级上，我们选择了具有长寿命的无机材料，研究了不同激发频率下寿命对发光亮度和效率的影响，得到了一个非常重要的结论。吸收是发光的前提条件，吸收变了，发光的其它特性也会跟着改变。然而发光寿命的长短会反过来影响吸收的次数多少，因此发光寿命将影响发光亮度及效率。下游的工作主要从对有机材料实现混合激发来提高发光亮度的思想开始深入的。首先在纯有机电致发光中，证明了实验中用到的三种稀土配合物电致发光的机理是：配体直接俘获载流子，再经分子内能量传递将能量从配体传递给稀土离子，得到了稀土离子的发光。我们将ZnS引入到有机电致发光器件中作电子功能层和空穴阻挡层，利用了ZnS层对电子的一次特性（电子传输）和二次特性（获得过热电子），提高了器件的发光亮度。在这种有机／无机复合的电致发光器件中实现了对稀土材料的混合激发：注入复合及碰撞激发。由于稀土离子特殊的电子分布，5d电子很难直接从外界吸收能量，因此稀土配合物中稀土离子的激发过程只能通过分子内的能量传递来敏化稀土离子。当配体上的电子到稀土离子的能量传递不充分时，配体激发态上的电子就可能通过别的方式去激发，这种去激发过程所引起的发光将影响稀土离子发光的色纯度。在Eu（o-BBA）₃（phen）的电致发光中出现了一个新的发光峰位于494nm的发光，经过各种实验验证，我们认为这个发光就是由于配体激发态上的电子到基质材料基态上的跃迁发光。为了获得色纯度高的红色电致发光，将Eu（o-BBA）₃（phen）与高效红光染料（DCJTB）共掺增强了红色发光，同时抑制了由于配体与稀土离子间能量传递不完全而引起的发光，得到了高亮度红色的电致发光器件，在20V的驱动电压下，发光亮度达到了650cd／m²。界面是有机电致发光研究中一个最基本的关键问题。在有机电致发光中，载流子的注入与输运是影响电致发光器件性能的关键因素。材料界面处的能级结构直接影响了载流子输运的全过程。实验发现C₆₀／PEDOT：PSS的空穴注入势垒是0.3eV，然而对于C₆₀/P3HT／PEDOT：PSS而言空穴注入势垒为1.7eV，这主要是由于在P3HT与PEDOT：PSS界面处存在一个-1.0eV的偶极层。P3HT／PEDOT：PSS的空穴注入势垒是0.2eV，而对于P3HT／pentacene／PEDOT：PSS而言空穴注入势垒为0.55eV，空穴注入势垒的变化主要是因为P3HT在不同衬底上的分子排布及pentacene／PEDOT：PSS界面偶极层引起的。从AFM图上我们也可以看到P3HT分子在这两种衬底上分子排布完全不同。P3HT在PEDOT：PSS衬底上无规则的分布，而在pentacene／PEDOT：PSS衬底上形成了沿pentacene晶粒上有规则的分布。对于pentacene／PEDOT：PSS和pentacene／P3HT／PEDOT：PSS而言，从PEDOT：PSS到pentacene的空穴注入势垒基本上没有变化，说明pentacene和P3HT界面的电荷转移非常弱，它们与PEDOT：PSS界面处的偶极层大小也很接近。Pentacene分子在硅片上的生长方式是分子长轴垂直于硅衬底，并形成了金字塔式的晶粒。这个结果与文献中报道的pentacene分子在金属衬底上生长的方式类似。当pentacene薄膜的厚度大于10nm以后，它的表面形貌基本上没有变化。本论文中共有图69幅，参考文献154篇。更多还原

【Abstract】 The main researches focus on the several methods to improve the intensity of solid state cathodoluminescence. The interfaces between small molecular and polymer were studied by using ultraviolet photoemission spectroscopy （UPS）. Investigations by atomic force microscopy （AFM） revealed morphology of organic materials on different substrates. The detailed researches on improvement of intensity and efficiency of solid state cathodoluminescence can be divided into three steps:The first step includes two research topics: the source of primary electrons and materials for accelerating electrons. From the transient spectra, we analyzed the source of the primary electrons and electrons acceleration ability of ZnS and SiO₂. These experimental results show the fact that primary electrons come from electrode, the electrons acceleration ability of SiO₂ is stronger than that of ZnS.The second step starts from the research on intrinsic factors which influence the intensity and efficiency of luminescence. We find out the applicable condition of molecular theory and band model for electroluminescence from solid state cathodoluminescence. The demarcation is the appearance of field ionization of excitons. The excitons emission obeys molecular theory and the recombination emission obeys band model. After consideration of luminescence lifetime of organic materials is on ns scale, we chose inorganic material with longer luminescence lifetime to study the effect of lifetime on intensity and efficiency under different driving frequency. Absorption is the underlying reason for the change of luminescent traits. And the lifetime influences on the absorption in turn. So the lifetime should influence the luminescent intensity and efficiency.The third work originates from our one idea about mixed exciation on organic materials. Firstly, we demonstrate that the electroluminescence mechanism of our studied rare earth complex is charge carriers captured by the ligand and then energy transferring from the ligand to rare earth ions. We introduce the ZnS into organic electroluminescence devices as electrons functional layer and hole blocking layer. The luminescence intensity and efficiency was improved by using the first and second electric properties of ZnS. For the inorganic-organic combined devices, there are two kinds of excitation mechanisms: injected recombination and impacted excitation. Due to the 5d electrons of rare earth ions shielded by 4f electrons, it is very difficult to absorb energy from environment for 5d electrons. The intramolecular energy transfer from the ligand to rare earth ions is sole way to excite rare earth ions. However, if the energy transfer from the ligand to rare earth ions is not very efficient, the electron on the excited state of ligand may transfer to the ground state of host molecular. In the case of electroluminescence of Eu（o-BBA）3（phen）, there is a new emission peak at 494nm. After detailed analysis, this emission should be attributed to electrons transition from the excited state of ligand to the ground state of host materials. This emission influences the color purity of emission from rare earth ions. In order to restrain this emission and obtain high intensity of red electroluminescence, a high efficient red dye （DCJTB） and Eu（o-BBA）3（phen） were co-doped into PVK. In the co-doping system, we obtained high intensity of red emission without PVK emission and 494nm emission. The EL intensityarrived to 650cd/m² when driving voltage is 20V.Interface energy alignment is one basic and key problem for organicelectroluminescence. It directly influences the injection and transporting of charge carriers. We found that the hole injection barrier for C₆₀ was drastically larger on P3HT pre-coated PEDOT:PSS （1.7 eV） compared to pristine PEDOT:PSS （0.3 eV）. This was facilitated by a large dipole （-1.0 eV） formed at the P3HT/PEDOT:PSS interface underneath the C₆₀ layer. This effect of deposition-sequence-dependent energy level alignment needs to be considered when using multi-heterolayers in organic functional devices. We attribute this to the fact that pentacene shows virtually the same interfacial dipole when deposited on PEDOT:PSS as does P3HT, and to a similar growth of PEN on both polymeric substrates. However, the valence band onset of P3HT was closer to EF on PEDOT:PSS （0.2 eV） compared to PEN pre-covered PEDOT:PSS （0.55 eV）. The ionization energy of P3HT on PEN/PEDOT:PSS was increased by almost the same amount. This was explained by different P3HT inter-molecular packing on the two substrates, which was corroborated by the observation by AFM of a disordered P3HT film on PEDOT:PSS and nanoscopic P3HT-related crystallites on PEN/PEDOT:PSS.Long axis of pentacene molecular is vertical with the surface of Si wafer. When the thickness of pentacene thin film goes beyond 10nm, the morphology keeps constant.更多还原