基于电极修饰提高聚合物发光二极管性能的机理研究

发布时间：2018-09-10 18:45

【摘要】：有机电致发光器件(organic light-emitting devices,OLEDs)作为新一代显示技术,与传统的显示技术相比,不但克服了视角窄、亮度低、工艺复杂等缺点,而且具有响应速度快、能耗低、全固态、厚度薄、自主发光、工作范围宽且可使用柔性基板等优越性。根据发光层材料的分子量的不同,OLEDs又可分为基于小分子材料的有机小分子电致发光器件(Small molecular OLEDs,Sm-OLEDs)和基于聚合物材料的聚合物电致发光器件(polymer light-emitting devices,PLEDs)。相比于小分子器件,PLEDs有着自身独特的优势,如制备工艺简单、成本低、利于大面积显示发展等。尽管PLEDs近年来的发展日新月异,但器件的性能如效率、寿命、以及稳定性等仍然有待提高。因此好的工艺手段和材料改进依然需要开发和研究。在工艺手段方面,对电极的修饰是非常有效的途径,可通过改善载流子的注入,提高载流子的平衡,从而提高器件的发光亮度、发光效率、寿命和稳定性等。电极修饰的方法众多,其中溶剂处理有机层表面,优化有机发光层/金属电极层界面,是一种简单、廉价并且高效的提高器件效率的方法,得到了人们的广泛关注和研究。基于此,本文主要通过电极修饰来提高PLED的器件性能。分别采用了极性溶剂处理法和优化电极电阻率法,提高了PLED器件的载流子注入平衡,从而提高了器件效率,并探究了其背后的工作机理。具体研究内容分为以下两个部分:一、以极性溶剂修饰发光层P-PPV的表面,来改善电子的注入,从而提高PLEDs器件的性能。相比于已报道的,以甲醇、乙醇或八氟戊醇等醇类极性溶剂为修饰溶剂的工作,我们采用非醇类、大偶极距的极性溶剂DMF来修饰绿色聚合物发光层P-PPV的表面。实验数据显示,对比无溶剂修饰的标准器件,甲醇修饰将器件的流明效率提高了17%,而DMF修饰将器件的流明效率提高了68%。考虑到DMF的沸点较高,为了控制DMF在P-PPV表面的残留量,我们将不同体积比的DMF掺杂在甲醇中,以DMF:甲醇的共混溶剂作为修饰溶剂来修饰P-PPV的表面。实验结果显示,相对于纯甲醇修饰,共混溶剂修饰进一步大幅度的提高了器件的发光效率。随着DMF在甲醇中的掺杂体积比从5%,10%,20%,40%提高到60%,相应的溶剂修饰后的器件的发光效率呈现抛物线形的变化规律,先增大再减小。掺杂比例为20%时,取得最高效率。修饰后PLEDs器件的发光效率相比于标准器件最多提高了126%,发光亮度最多提高了81%。可以见得,简单的极性溶剂处理法却能带来器件性能显著的提高。通过研究溶剂修饰对P-PPV发光层的表面形貌和粗糙度、紫外可见吸收、表面电势和表面电子结构的影响,以及PLED器件的电子电流密度和开路电压等的变化,深入而系统的研究了溶剂修饰提高PLEDs发光效率的原因。二、基于p型Si(p-Si)阳极的PLEDs。传统的PLEDs采用铟锡氧化物(ITO)透明导电电极,其中的铟元素为在地壳中含量稀少,随着ITO的广泛使用,更加暴露了这一问题。而Si元素在地壳中的含量仅次于氧,占比26%。因此,以Si为阳极,不存在源材料短缺的问题。我们以p-Si为阳极,制备了高效率的PLEDs。我们研究了p-Si阳极的电阻率对PLED器件性能的影响。实验结果显示随着p-Si电阻率的增加,相同电压下,器件的电流密度单调增加,而发光亮度和效率先增后减。当p-Si电阻率为0.1Ω?cm-3,得到最佳功率效率。
[Abstract]:Organic light-emitting devices (OLEDs) as a new generation of display technology, compared with traditional display technology, not only overcome the shortcomings of narrow viewing angle, low brightness, complex technology, but also has the advantages of fast response, low energy consumption, all solid-state, thin thickness, self-luminescence, wide operating range and flexible substrate. According to the different molecular weight of the luminescent layer materials, OLEDs can be divided into organic small molecule OLEDs (Sm-OLEDs) and polymer light-emitting devices (PLEDs). Compared with small molecule devices, PLEDs have their own unique characteristics. Advantages, such as simple fabrication process, low cost, conducive to the development of large area display and so on. Despite the rapid development of PLEDs in recent years, the performance of devices such as efficiency, life, and stability still need to be improved. Therefore, good process means and material improvement still need to be developed and studied. There are many methods of electrode modification, among which solvent treatment of organic layer surface and optimization of the interface between organic light emitting layer and metal electrode layer are simple, cheap and efficient. Based on this, this paper mainly uses electrode modification to improve the performance of PLED devices. The polar solvent treatment method and the optimized electrode resistivity method are used respectively to improve the carrier injection balance of PLED devices, thereby improving the device efficiency and exploring the working mechanism behind them. The specific research contents are divided into the following two parts: 1. Polar solvents are used to modify the surface of phosphorescent layer P-PPV to improve the performance of PLEDs by improving the injection of electrons. DMF is used to modify the surface of green polymer light emitting layer P-PPV. The experimental results show that compared with the standard device without solvent modification, the luminous efficiency of the device is increased by 17% by methanol modification and 68% by DMF modification. The surface of P-PPV was modified by DMF doped in methanol with DMF:methanol as modifier. The experimental results showed that compared with pure methanol, the luminous efficiency of the device was further improved greatly. With the doping volume ratio of DMF in methanol increased from 5%, 10%, 20%, 40% to 60%, the corresponding solvent repair was carried out. The luminous efficiency of the modified PLEDs is increased by 126% and the luminous brightness is increased by 81% compared with the standard devices. It can be seen that simple polar solvent treatment can bring the device performance. The effect of solvent modification on the surface morphology and roughness, UV-Vis absorption, surface potential and surface electronic structure of P-PPV luminescent layer, as well as the changes of electronic current density and open-circuit voltage of PLED devices were studied. The reasons for the improvement of PLEDs luminescent efficiency by solvent modification were studied in detail and systematically. I(p-Si) anode PLEDs. Conventional PLEDs use indium tin oxide (ITO) transparent conductive electrodes, in which indium is scarce in the crust. With the widespread use of ITO, this problem is further exposed. The content of silicon in the crust is only second to that of oxygen, accounting for 26%. Therefore, there is no shortage of source materials for the Si anode. The effect of resistivity of p-Si anode on the performance of PLED devices was studied. The experimental results show that the current density increases monotonously with the increase of p-Si resistivity, while the luminous brightness and efficiency increase first and then decrease with the increase of p-Si resistivity. When p-Si resistivity is 0.1_?Cm-3, the optimal power efficiency is obtained.
【学位授予单位】：南京邮电大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN383.1

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