【作者】 李爱源；

【导师】 彭俊彪；

【作者基本信息】 华南理工大学 ， 材料物理与化学， 2010， 博士

【摘要】 有机电致发光作为近年来的研究热点,一方面在科研方面有着重要意义,在有机材料合成以及器件物理上遇到许多新问题,创造了许多新知识,另一方面,作为液晶显示后的新一代平板显示技术,以及作为新型白光照明技术,具有诱人的应用前景。目前,部分的有机电致发光的技术已经进入商业化的阶段,如索尼公司已经推出了基于蒸镀小分子材料的OLED显示器,Lumiotec公司也推出了用于照明的OLED白光光源。但有机电致发光仍然存在着许多问题,诸如寿命和发光效率仍需要进一步的提升。PLED是“双载流子注入”型器件,在正向偏压的作用下电子和空穴分别从阴极和阳极注入,并由于电场的作用向对面电极迁移,在发光层中复合成激子,激子的辐射衰减得到发光。因此,器件的效率很大程度上取决于载流子的平衡与否。基于此思想,人们可以通过增加器件内少数载流子或者减少多数载流子的办法实现器件效率的提高。聚芴及其衍生物由于具有较低的三线态能级,其作为主体材料时候,若客体磷光材料的三线态能级高于主体三线态能级,会造成能量回转从而导致器件的发光淬灭。因此一般情况下,聚芴及其衍生物并不适合作为绿色磷光材料的主体。本论文中第3章中,我们通过在空穴注入层PEDOT:PSS和发光层中插入一层具有高三线态能级的PVK作为缓冲层,能成功的抑制发光层内的能量回转导致的发光淬灭,从而实现高效白光发射。通过插入电子注入材料PFN,器件效率进一步提高,实现在电流密度10 mA/cm2下色坐标为(0.262,0.310),最高电流效率为15.1 cd/A的白光发射。OLED的制备工艺主要有溶液加工和真空蒸镀两种,前者可以实现任意比例的精确掺杂,缺点是难以形成多层结构,成膜厚度比较难精确控制,后者可以实现厚度的精确的控制以及形成多层结构,但难以实现精确的微量掺杂。在本论文的第4章中,我们结合了两种制备工艺,在高效蓝光聚芴衍生物中掺杂红光材料MEH-PPV,在旋涂此发光层的基础上,再蒸镀绿光材料Alq3,通过调节Alq3的厚度,从而调节器件的发光颜色,并获得非常接近色坐标(0.33,0.33)的白光发射,通过加入缓冲层,实现了最高电流效率为7 cd/A,在10m A/cm2下色坐标为(0.35,0.37)的白光发射。通过掺杂的办法使得器件工作时候内部的载流子数趋于平衡是实现器件发光效率提高的一种行之有效的办法。在各种掺杂的办法中,掺入一维纳米线的办法属于一种比较少人涉足的领域。在Jian Wang的工作基础上,在本论文的第5章中,我们在含有不同BT含量的n型发光材料PFO-BT中掺入不同质量浓度的有机可溶液加工p型纳米线,在掺入比例为1%时候实现发光效率的最大提高。我们进一步采用交流阻抗的方法对此体系进行表征,从Cole-Cole图的结果,我们推断器件可以等效成一个固定小电阻和一个RC并联电路的串联,其中的小电阻对应于衬底的方块电阻和接触电阻的和,RC并联电路代表发光层,我们发现随着纳米线掺杂浓度微小增大,R值呈2到3个数量级的增大。说明纳米线在体系中起到阻碍电子电流的作用,这跟器件的J-V-L有很好的吻合。有机电致发光的效率的提高可以通过增加器件内少数载流子的办法实现。在本论文第6章中,我们在Xuihui Zhu的工作基础上,通过更换阴离子的办法,重新制备了3种新型可溶性有机小分子电解质作为电子注入材料。通过跟纯A1器件和以溴离子为阴离子的电子注入材料作对比,我们发现新制备的电子注入材料同样具有很好的电子注入能力,其中阴离子为四氟硼酸根的电子注入材料跟溴离子的注入能力相当,并且器件在高电流密度下仍然保持有较高的电流效率。通过OPV测试考察器件的内建电场,我们发现四氟硼酸根具有最大的内建电场,即具有最好的电子注入能力。更多还原

【Abstract】 Organic Light-Emitting Diode has raised focus in scientific research since it encountered many new problems both in chemical synthesis and device physics, it also created much new knowledges. On the other hand, as a new generation display techonology after liquid crystal display and new technology in white light illumination, it shows attractive prospect. For example, Sony has its flat panal display product based on OLED and Lumiotec has its white light source product based on OLED. However, there still have many things to be improved, such as the lifetime and the efficiency of the devices.PLEDs are "dual injection" devices with electrons and holes injecting from the cathode and anode, respectively, under forward bias. Then, the carriers move in the emissive layer toward the opposite electrode, and form exciton with pairs of electron and hole. The radiant decay of exciton gives out light. So it is a key element wheather the carriers are balance for the efficiency of the devices. Based on this mechanism, people can enhance the efficiency of the devices by increasing the minority carriers or decreasing the majority carriers.Polyfluorene and its derivatives have relatively lower triplet level, when it is used as the host in phosphorescent OLED, if the gust materials has triplet level higher than the host, emission quench happened in the form of back energy transfer from the guest to host. This is why Polyfluorene and its derivatives are not suitable to be the host of the green phosphorescent materials. In chapter3 of this thesis, we successfully inhibit the energy back transfer from the green phosphorescent material to our polyfluorene derivative host by inserting a buffer layer between the hole injection layer PEDOT:PSS and the active layer and fabricated a highly efficient white polymer light emitting diode. By further inserted a water-acohol soluable electron injection layer PFN, we got white emission with CIE of (0.262,0.310) at the current density of 10mA/cm2, and the highest efficiency of 15.1 cd/A.There are mainly two proces to fabricate OLED i.e solution processing and vacuum deposition. The former can achieve an arbitrary ratio of precice doping and the disadvantage is that it is difficult to form multi-layer structure and difficult to control the film thickness accurately. The vacuum deposition allows precise control of thickness and formation of multi-layer structure, but it is difficult to achieve accurate trace dopping. In chapter 4 of this thesis, we first ly spin coated the high efficiency blue material dopped with red emission material MEH-PPV, then we deposited the green emission layer Alq3, by controlling the thickness of the Alq3, we successfully tuned the color of the devices and got white emission closed to CIE of (0.33,0.33). By insertin buffer layer TPBI and PVK, we realized the highest current efficiency of 7cd/A, and CIE of (0.35,0.37) white emission at the current density of 10mA/cm2.It is an effective way to enhance the efficiency of PLED by dopping. To dope one dimentional nanowires into the emitting materials is a relatively small area involved. Following the work of Jian Wang, in chapter5 of this thesis, we use PFO-BT with different BT ratios, and dopped with a soluable nanowire material in different ratios. We found that with dopping ratio of 1%, devices based on different BT ratio got the highest efficiency. We further characterize the devices with ic impedance spectro. From the Cole-Cole diagram, we infer that the devices can be equivalent to be a low resistance and a parallel RC circuit in series. The low resistance corresponds to the sum resistance of the substrate and the contact resistance, RC parallel circuit corresponds to the emitting layer. We found that the R in RC parallel increased 2-3 orders with small increase of the dopping ratio of nanowires, which means that the nanowires in the system enhanced the efficiency by stopping the electron crrurent in the devices and with good agreement with the J-V-L curves.We can enhance the efficiency of the OLED by increasing the minority carriers. In chapter 6 of this thesis, based on the work of Xuihui Zhu, we made 3 new small molecular soluable electrolytes as electron injection material by replacing the anion. By compareing with the bare Al and the reported electrolyte, we found that the new electrolytes also have good electron injection ability. Among them, the one with tetrafluoroborate as anion shows the best injection ability, the devices based on it remains highly efficient even at high current density. Further more, we carried the OPV measurement to determine the buit-in potential, we found the one with tetrafluoroborate as anion has the largest built-in potentials, which means the best electron injection ability.更多还原