【作者】 王欢；

【导师】 马於光；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2011， 博士

【摘要】 有机晶体中分子排列的高度有序以及低的杂质含量,保证了晶体本身具有高的载流子迁移率和高的热稳定性；同时晶体明确的分子堆积结构,为我们研究材料-些本征的特性,如分子间基本的相互作用力、分子排列方式对光电性质(分子聚集体的发光效率和载流子迁移率)的影响规律等提供了模型。发展具有高发光效率高载流子迁移率、低光泵激光阈值的有机晶体材料对于电注入发光与激光的研究具有十分重要的意义。物理气相传输(PVT)法是生长大尺寸、高质量有机晶体的常用方法,而且得到的晶体通常具有厚度薄、表面平滑的特点,非常适合于器件的制备；本论文结合PVT法生长晶体的特点,选择反式二苯乙烯基苯(trans-DSB)作为主体、并四苯(tetracene)和并五苯(pentacene)分别作为客体,考虑了主客体材料在分子结构和堆积方式上的兼容性,利用能量转移制备了具有高发光效率的掺杂晶体,详细讨论了掺杂晶体的光物理性质和载流子迁移性质。主要内容如下：1.以PVT法生长的具有薄片状外形的有机晶体作为模型,分析了在晶体形成过程中的结构和热动力学因素；并且基于trans-DSB、tetracene、pentacene这三种分子相似的线性构型和晶体中“鱼骨刺”(herringbone)形排列方式,分别制备了从蓝光到红光波段颜色可调及白光发射的有机掺杂晶体。2.掺杂晶体通过能量转移实现高发光的同时降低了自吸收,展现了优异的放大自发射性质；同时主客体分子间相互垂直的偶极排列方式导致了取向因子κ2和Forster临界能量转移半径R0都较小,因此在掺杂晶体中较高浓度的掺杂才能保证有效地能量转移；而PVT法正是在高温条件下生长晶体,并且主客体分子在结构上的兼容性保证了较小的晶格失配,具有较高动能的客体分子有利于嵌入到主体晶格中,从而实现了高浓度掺杂。3.掺杂晶体与未掺杂的主体晶体相比,载流子迁移率处于同一数量级,这是因为客体分子掺杂到主体晶体中没有破坏其晶格结构的完整性；掺杂晶体利用能量转移实现高发光效率的同时保持了晶体高迁移率的特征,即在掺杂晶体的体系中实现了高发光和高迁移的统一,是有希望用于电注入发光与激光研究的材料。更多还原

【Abstract】 Organic crystal with highly ordered molecular arrangement and low impurity content has the high carrier mobility and high thermal stability, and with clear crystal structure also has provided a model to investigate the intrinsic properties of material, such as the basic intermolecular interactions, the relationship between the molecular stacking modes and the optoelectronic properties (luminescent efficiency and carrier mobility).Organic crystals with high luminescent efficiency, high carrier mobility and low amplified spontaneous emission (ASE) threshold could be as promising materials for the electrically pumped laser which has not yet been achieved. The molecular stacking mode could be adjusted by introducing the special intermolecular interactions, to improve the luminescent efficiency and carrier mobility of the crystal, but in the view of supramolecular chemistry and crystal engineering, designing the intermolecular interaction by the chemical synthesis to control the molecular stacking mode in the crystal is more complicated. As we know, physical doping is a very effective approach to realize the high solid-state luminescent efficiency. However, in terms of the organic crystal, the lattice mismatch and the weak intermolecular interaction which are the reasons for the difficulties of large-size doping crystal growth should be considered.The three molecules of trans-1,4-Distyrylbenzene (trans-DSB), tetracene and pentacene have similar linear configurations and’herringbone’intermolecular arrangements in the crystals. The emission spectrum of trans-DSB overlaps well with the absorption spectra of tetracene and pentacene, and thus the three materials are ideal for preparing the large-size doping crystals by choosing the appropriate crystal growth conditions.Physical vapor transport (PVT) is the common method to grow the large-size and high-quality organic crystal which usually has the characteristics of thin thickness and smooth surface and is suitable for the fabrication of the device. Because the crystal growth process is carried out under the high temperature condition, the molecules in vapor have the high kinetic energy and are conducive to a more stable stacking mode during the formation of the crystal. Based on the characteristics of PVT method to crystal growth, trans-DSB as the host, tetracene and pentacene as the guest, respectively, have been chosen, and the guest molecules with high kinetic energy benefit to embed into the host lattice which has been intensely disturbed due to the high-temperature growth condition. Meanwhile the host and guest molecules are structural compatibility to ensure the smaller lattice mismatch that the high doping concentration could be achieved in the crystal. Atomic force microscopy (AFM) and X-ray diffraction (XRD) results show that the ordered structures of doped crystals are retained but a slight increase of layer spacing compared with the undoped trans-DSB crystal, indicating that the guest molecules embedded into the host lattice occupy the original location of host molecules in the crystal growth process. As tetracene and pentacene molecules in the doped crystals avoid the self-aggregation induced luminescence quenching, and the luminescent efficiencies of tetracene-doped trans-DSB and pentacene-doped trans-DSB crystals reach to 74% and 28% by the energy transfer, respectively. The ASEs are also observed due to the decrease of the self-absorption in the doped crystals. The mutually perpendicular host-guest molecular dipole arrangements result in that the orientation factorκ2 (0.004-0.008) and the Forster distance R0 (1.5-1.8 nm) are small, and thus higher doping concentration in doped crystals compared with amorphous doped films are necessary to ensure the energy transfer efficiently. Further, the white-emission doped crystal could be obtained by controlling the molar ratio of host and guest molecules (tetracene:pentacene:trans-DSB = 1:1.35:23.1). There are the energy transfers not only from trans-DSB to tetracene and pentacene, but also from tetracene to pentacene by the analysis of time-resolved fluorescence spectra of the white-emission doped crystal.Then the field-effect transistors and diodes based on doped crystals with high luminescent efficiency are fabricated to investigate the influence of guest doping concentration and crystal thickness on the carrier mobility. In the FETs devices, the hole mobility for the undoped trans-DSB crystal is about 6.67×10-3 cm2/Vs and those for the doped crystals with almost entire energy transfer are about 1.41×10-3 cm2/Vs (molar ratio, tetracene:trans-DSB= 1:15) and 1.17×10-3 cm2/Vs (molar ratio, pentacene:trans-DSB= 1:13), respectively. Although the mobility of doped crystal decreases slightly, it is still in the same order of magnitude with that of the undoped crystal, because the guest molecules embedded in doped crystals don’t destroy the whole crystal ordered structure. Doped crystals by energy transfer achieve high luminescent efficiency while maintain the characteristics of high mobility, which are promising materials for the electrical injection luminescence and laser research. In the diodes devices, the mobility increases with the crystal thickness at the same electrical field because the relatively thicker crystal can reduce the influence of interface contact between the ITO/PEDOT electrode and the crystal on the charge injection. Further, taken cyano substituents oligo (para-phenylene vinylene) (CN-DPDSB) crystal with low ASE threshold (23 KW/cm2), high luminescent efficiency (-95% ) and bipolar carrier transport balance (μelectron≈0.9-1.3×10-2 cm2/Vs;μhol≈2.5-5.5×10-2 cm2/Vs) for example, the diode device structure can endure the current density of～5 KA/cm2, which still has a great gap with the threshold current required to the organic electrically pumped laser (～102-103 KA/cm2). However, it is analyzed that the requirements to organic crystals applied in electrically pumped laser include:i) developing crystal materials with high luminescence, high mobility and low ASE threshold; ii) improving the interface contact of crystal device to increase the effective charge injection.更多还原