基于金属卤化物钙钛矿材料的高效发光二极管

金属卤化物钙钛矿半导体既在光伏器件研究中获得巨大进展,又在发光应用中体现出明显优势。金属卤化物钙钛矿半导体的荧光转化效率高、发光峰形窄、发射光谱可调控并可覆盖整个可见光范围,从而使得该类材料所制备的发光二极管有望满足下一代显示技术应用的性能要求。文章在简要叙述发光二极管基本原理的基础上,分别介绍了钙钛矿材料的结构和荧光特性、钙钛矿发光二极管的电致发光特性,以及钙钛矿发光二极管进入实际应用所必须解决的器件寿命、离子迁移和光谱不稳定性等主要技术问题,最后讨论了钙钛矿发光技术所面临的机遇和挑战。     

基于激子阻挡层的高效率绿光钙钛矿电致发光二极管

金属卤化物钙钛矿材料由于具有高的光致发光量子产率、高色纯度、带隙可调等杰出的光学性能,被作为发光材料广泛地用于制备钙钛矿电致发光二极管(perovskite light-emitting diodes,PeLEDs).虽然取得了较好的研究进展,但是其效率和稳定性还未达到商业化的要求,还需要进一步提高.为了提高PeLEDs的效率和稳定性,本文使用旋涂法,引入了一种具有宽带隙和较好空穴传输能力的有机小分子材料4,4′-cyclohexylidenebis[N,N-bis(p-tolyl)aniline](TAPC)作为激子阻挡层,获得了效率和寿命都得到提高的全无机PeLEDs.研究表明,PeLEDs效率和寿命得到提高的物理机制主要源于两方面:1)TAPC具有恰当的最高占有分子轨道能级,与PEDOT:PSS的最高占有分子轨道能级和CsPbBr3的价带边形成了阶梯式能级分布,有利于空穴注入和传输;同时TAPC具有较高的最低未占分子轨道能级,能够有效地阻止电子泄漏到阳极端,并能很好地将电子和激子限制在发光层内;2)TAPC层的引入可以避免钙钛矿发光层与强酸性的空穴注入材料Poly(3,4-ethylenedioxythiophene):poly(p-styrene sulfonate)(PEDOT:PSS)的直接接触,进而免除钙钛矿发光层由于与PEDOT:PSS的直接接触所导致的激子淬灭,从而提高了激子的发光辐射复合率.     

利用温变电容特性测量发光二极管结温的研究

结区的温度, 简称结温, 是发光二极管(LED) 的重要参数之一, 它对LED 器件的出光效率、光色、器件可靠性和寿命均有很大影响, 准确测量LED 器件的结温对制备LED 芯片、器件封装和应用有着重要的意义. 本文利用反向偏压下的LED的势垒电容随温度变化的特性, 提出了一种LED结温测量的新方法. 论文首先测量和分析了LED在室温下反向偏压时的电容-电压(C-V)曲线和不同反向偏压下的电容-温度(C-T)曲线, 结果表明, 在合适的偏压下, LED的电容随温度的增大而显著增加, 并呈现良好的线性关系. 在LED工作中监测其电容的变化, 并与C-T曲线进行对比, 实现了LED结温的测量, 其测量结果和传统的正向电压法的结果相对比, 两者符合较好. 最后, 利用上述方法测量了LED 在恒流和恒压条件下的结温的实时变化过程. 较传统的结温测量方法, 本方法的优点在于只须要一次定标测量, 且可实现LED在任意电压和电流下的结温测量.     

Multiple roles of bathocuproine employed as a buffer-layer in organic light-emitting diodes

Efficiency and brightness and carriers injection have been obviously improved by using bathocuproine (BCP) as a buffer-layer in organic light-emitting diodes. Compared with the bufferless device, the quantum efficiency of device ITO/NPB (10 nm)/Alq₃ (10 nm)/BCP (2.4 nm)/Al has increased four times at the same current density (32 mA/cm²). Moreover, the buffer layer has changed the current-voltage properties and the turn-on voltage has obviously decreased. Considering BCP and Al³⁺ can react conveniently under room temperature, we suggest that a complex cathode structure of BCP/[(Al)_x(BCP)_y]^3x+/Al has formed under electric field and the new cation [(Al)_x(BCP)_y]^3x+ at the BCP/Al interface has improved the internal electric field and then enhanced the electrons injection. we conclude that: for a very thin (<1 nm) BCP buffer layer, improving electron injection will principally responsible to the improvement of the performance of the OLEDs; for a thicker BCP layer, there will be a synthetic function of BCP: improving electron injection, hole-blocking and electron-transporting.     

掺杂二氧化钛纳米管对有机电致发光性能的影响

在聚合物电致发光器件中，通过在不同功能层中掺杂二氧化钛纳米管来改善器件的性能.由于二氧化钛纳米管具有p型传导特性，可以显著增大空穴传输层中载流子的迁移率.由于二氧化钛纳米管在发光层中可以增大发光材料分子的刚性，从而减少无辐射跃迁.当把二氧化钛纳米管掺杂到空穴缓冲层中时，由于其与有机分子的强相互作用，一方面降低了空穴的传导性，同时也减少了界面淬灭发光的缺陷态的产生. 关键词： 二氧化钛纳米管 聚合物电致发光 掺杂     

高分子发光二极管载流子注入过程研究

采用交流阻抗谱，电容-电压，电容-频率等实验方法，研究了共轭高分子MEH-PPV(poly［2-methoxy，5-(2-ethylhexoxy)-1，4-phenylene vinylene］)发光二极管的载流子注入过程.对于结构为ITO/PEDOT/MEH-PPV/Ba/Al的发光器件，实验结果表明，电极界面是欧姆接触的，载流子的注入是非平衡的，器件薄膜中存在陷阱容易俘获注入电荷，形成空间电荷区，陷阱密度约为3.75×10¹⁶cm^-3. 关键词： 高分子发光二极管 交流阻抗谱 cole-cole图 载流子注入     

The advantage of blue InGaN multiple quantum wells light-emitting diodes with p-AlInN electron blocking layer

InGaN based light-emitting diodes (LEDs) with different electron blocking layers have been numerically investigated using the APSYS simulation software. It is found that the structure with a p-AlInN electron blocking layer showes improved light output power, lower current leakage, and smaller efficiency droop. Based on numerical simulation and analysis, these improvements of the electrical and optical characteristics are mainly attributed to the efficient electron blocking in the InGaN/GaN multiple quantum wells (MQWs).     

Ligand effect on the performance of organic light-emitting diodes based on europium complexes

A series of europium complexes were synthesized and their electroluminescent (EL) characteristics were studied. It was found by comparison that the different substituted groups, such as methyl, chlorine, and nitryl, on ligand 1,10-phenanthroline affect significantly the EL performance of devices based on these complexes. The more methyl-substituted groups on ligand 1,10-phenanthroline led to higher device efficiency. A chlorine-substituted group showed the approximate EL performance as two methyl-substituted groups, whereas a nitryl substituent reduced significantly the EL luminous efficiency. However, β-diketonate ligand TTA and DBM exhibited similar EL performance. The improved EL luminous efficiency by proper substituted groups on the 1,10-phenanthroline was attributed to the reduction of the energy loss caused by light hydrogen atom vibration, as well as concentration quenching caused by intermolecular interaction, and the match of energy level between the ligand and Eu³⁺.     

Improvement in electroluminescence performance of n-ZnO/Ga_2O_3 /p-GaN heterojunction light-emitting diodes

n-ZnO/p-GaN heterojunction light-emitting diodes with and without a Ga2O3 interlayer are fabricated. The electroluminescence （EL） spectrum of the n-ZnO/p-GaN displays a single blue emission at 430 nm originating from GaN, while the n-ZnO/Ga2O3/p-GaN exhibits a broad emission peak from ultraviolet to visible. The broadened EL spectra of n-ZnO/Ga2O3/p-GaN are probably ascribed to the radiative recombination in both the p-GaN and n-ZnO, due to the larger electron barrier （ΔEC=1.85 eV） at n-ZnO/Ga2O3 interface and the much smaller hole barrier （ΔEV=0.20 eV） at Ga2O3/p-GaN interface.     

白光有机电致发光器件的载流子传输与复合特性

基于一种将具有电荷传输性的双极性主体材料与蓝、黄光客体材料共蒸的单层结构的同质结结构,制备了色温可调的白光有机电致发光器件(OLED)。由于不存在激子阻挡层,单层结构容易发生漏电流现象,致使OLED器件具有较高的工作电压和较低的电流/功率效率。在空穴/电子传输层进行p/n型掺杂的同质结结构则大大改善了器件性能。研究表明: 该种器件结构获得了相对较低的起压5.6 V,较高的电流效率2.64 cd/A和低效率滚降,其色坐标则随着亮度的增加沿着普朗克轨迹变化,产生类似于太阳光的发光特性。另外,对主体材料和共蒸层的电荷载流子的传输特性和复合机制也进行了一系列分析研究。     

一种基于荧光材料的聚合物白光发光二极管

制备了一种基于荧光聚合物共混的单发光层聚合物白光发光二极管.器件结构为铟锡氧化物/苯磺酸掺杂聚乙烯基二氧噻吩/发光层/ 1,3,5-三(N-苯基-2-苯并咪唑-2)苯41/Ba/Al,蓝光材料芴-氟化喹喔啉共聚物(PF-BPFQ5)、绿光材料苯基取代的聚对苯乙炔(P-PPV)和红光材料聚(2-甲氧基-5-(2′-乙基己氧基)-1,4-对苯乙炔)(MEH-PPV)共混为发光层.当PF-BPFQ5,P-PPV,MEH-PPV的质量比例为100∶06∶06时,获得标准的白光,色坐标为（033 关键词： 聚合物发光二极管 白光 共混     

Improved performance of organic light-emitting diodes with dual electron transporting layers

In this study the performance of organic light-emitting diodes(OLEDs) are enhanced significantly,which is based on dual electron transporting layers(Bphen/CuPc).By adjusting the thicknesses of Bphen and CuPc,the maximal luminescence,the maximal current efficiency,and the maximal power efficiency of the device reach 17570 cd/m2 at 11 V,and 5.39 cd/A and 3.39 lm/W at 3.37 mA/cm2 respectively,which are enhanced approximately by 33.4%,39.3%,and 68.9%,respectively,compared with those of the device using Bphen only for an electron transporting layer.These results may provide some valuable references for improving the electron injection and the transportation of OLED.     

激光诱导p-GaN掺杂对发光二极管性能改善的分析

采用激光诱导掺锌的方法提高了常规GaN基外延片p-GaN层的空穴浓度,并将它制备成小功率白光发光二极管(LED).对其光电性能做了详细的测量并进行了加速老化实验和分析.结果表明,与常规LED相比,经过激光诱导p-GaN层掺锌LED的光电性能获得了明显改善:正向工作电压VF从3.33V降到3.13V,串联电阻从30.27Ω降到20.27Ω,室温下衰退系数从1.68×10-4降到1.34×10-4,老化1600h后的反向漏电流从超过0.2μA降为不超过0.025μA,器件的预测寿命延长了41%.器件光电性能改善的主要原因是激光诱导掺锌使LED的p-型欧姆接触改善和热阻降低所致.     

Improved performance of InGaN light-emitting diodes with a novel sawtooth-shaped electron blocking layer

A sawtooth-shaped electron blocking layer is proposed to improve the performance of light-emitting diodes （LEDs）. The energy band diagram, the electrostatic field in the quantum well, the carrier concentration, the electron leakage, and the internal quantum efficiency are systematically studied. The simulation results show that the LED with a sawtooth-shaped electron blocking layer possesses higher output power and a smaller efficiency droop than the LED with a conventional A1GaN electron blocking layer, which is because the electron confinement is enhanced and the hole injection efficiency is improved by the appropriately modified electron blocking layer energy band.     

The effect of alkaline metal chlorides on the properties of organic light-emitting diodes

The multilayer organic light-emitting diodes (OLEDs) have been fabricated with a thin alkaline metal chloride layer inserted inside an electron transport layer (ETL), tris (8-hydroxyquinoline) aluminum (Alq₃). The alkaline metal chloride layer was inserted inside 60 nm Alq₃ at d=0, 10, 20 and 30 nm positions (d is the distance of the interlayer away from the Al cathode). The devices, with alkaline metal chlorides inserted at the Alq₃/Al interface, showed electron injection and electroluminescence (EL) intensity improvements. When the alkaline metal chlorides were inserted inside the Alq₃ layer at 10, 20 or 30 nm position apart from the Al cathode, both EL intensity and efficiency were enhanced for the devices with a thin potassium chloride (KCl) or rubidium chloride (RbCl) layer. On the contrary, the improvements were not observed for the OLEDs with a thin sodium chloride (NaCl) layer. A proposed insulator buffer layer model is employed to explain these characteristics of the devices.     

Temperature-dependent electrical properties of organic light-emitting diodes depending on cathodes

We have studied temperature-dependent electrical properties of organic light-emitting diodes with a variation of cathode materials; Al, LiAl, and LiF/Al. The organic light-emitting diodes emit a light by a recombination of injected charge carriers such as holes and electrons. Thus, the charge transport is affected by the injection barrier at the interface. By varying the cathode materials, the electron injection at the interface could be controlled because of the work-function change at the cathode. Temperature-dependent current–voltage luminance characteristics of the organic light-emitting diodes were measured in the temperature range from 10 to 300 K. The current-voltage characteristics were analyzed in terms of Fowler–Nordheim tunneling model, and the energy-barrier height was obtained. A measured lifetime of device with LiF/Al cathode is relatively longer than the other cathodes at room temperature: 4.5 h for Al cathode, 12.4 h for LiAl, and 29.6 h for LiF/Al. The device with LiAl and LiF/Al cathode, in the aspect of lifetime and luminous efficiency, is superior to one of other cathodes.     

量子点发光二极管稳定性提高策略

量子点发光二极管(QLEDs)由于具有独特的光电特性,可应用于照明和显示行业,其外量子效率(EQEs)正迅速接近商业化要求.然而,器件的稳定性和工作寿命仍然是QLEDs商业化应用面临的关键问题.本文将影响QLEDs寿命的主要因素分为功能层材料的稳定性和电荷注入不平衡两大方面,从提高量子点、电荷传输层(CTLs)的稳定性...     

渐变型量子阱垒层厚度对GaN基双波长发光二极管发光特性调控的研究

采用软件理论分析的方法对渐变型量子阱垒层厚度的InGaN双波长发光二极(LED)的载流子浓度分布、 能带结构、自发发射谱、内量子效率、发光功率及溢出电子流等进行研究.分析结果表明, 增大量子阱垒层厚度会影响空穴在各量子阱的注入情况, 对双波长LED各量子阱中空穴浓度分布的 均衡性及双波长发光光谱的调控起到一定作用,但会导致内量子效率严重下降; 而当以特定的方式从n电极到p电极方向递减渐变量子阱垒层厚度时, 活性层量子阱的溢出电子流 得到有效的控制, 双发光峰强度达到基本一致, 同时芯片的内量子效率下降得到了有效控制, 且具备大驱动电流下较好的发光特性.     

非周期微纳结构增强有机发光二极管光耦合输出的研究进展

有机发光二极管（OLED）具有功耗低、重量轻、色域宽、响应时间快及对比度高等优点,在全彩平板显示和固态照明等领域均显现出巨大的应用潜力,受到人们的广泛关注.然而,较低的光输出效率使得器件的外量子效率远低于内量子效率,这严重制约了OLED器件的发展和应用.因此如何提高OLED器件的光耦合输出效率已成为备受关注的研究课题.本文主要介绍了采用非周期微纳结构提高OLED器件光耦合输出效率的最新研究进展,对随机微纳透镜结构、光散射介质层、聚合物多孔散射薄膜、随机凹凸波纹结构及随机褶皱结构等多种对器件亮度分布和光谱稳定性无明显影响的光耦合输出技术进行了总结和讨论.最后,对提高OLED器件光耦合输出研究做了总结和展望.