混合量子点QLED结构性能研究

为研究基于混合量子点的QLED结构与性能,利用红光量子点以及绿光量子点两种材料制备了橙光QLED器件,并对其性能进行了表征。实验制备的器件结构为ITO/PEDOT∶PSS/poly-TPD/混合QDs/Zn O/Al,其中发光层采用了3种混合量子点的混合结构方案。方案一先旋涂红光量子点层,后旋涂绿光量子点层;方案二先旋涂绿光量子点层,后旋涂红光量子点层;方案三将红光、绿光量子点1∶1混合后制备为发光层。实验结果表明:方案一制备的器件电流密度最大,发光亮度最低,且只有红光谱;方案二制备的器件具有最小的电流密度,同时具有红、绿光谱,在8 V电压下,电流效率约为4.69 cd/A;方案三制备的器件同时具有红、绿光谱,电流密度与发光特性介于方案一与方案二之间。实测数据与理论分析是一致的,方案二制备的器件存在双能量陷阱,能够将注入的空穴以及电子同时限制在红光量子点层内。通过调节各功能层厚度使得载流子注入平衡,可进一步增大发光电流,提高器件效率。     

Highly efficient white quantum dot light-emitting diode based on ZnO quantum dot

White quantum dot light-emitting diodes (QD-LEDs) have been a promising candidate for high-efficiency and color-saturated displays. Here, we report a simply solution-processed white QD-LED using ZnO QDs as emitters. The device is demonstrated with a maximum luminance of 300 cd/m², exhibiting the Commission Internationale de l’Enclairage coordinates of (0.33, 0.33). The unencapsulated white QD-LED has a long lifetime of 120 h. These results indicate that ZnO QDs provides an alternate and effective approach to achieve high-performance white QD-LEDs and also other optoelectronic devices.     

倒置器件结构及局域等离子体效应对CdSe量子点LED发光性能的改进

研究了倒置器件结构以及CdSe量子点发光材料与金属纳米粒子之间的相互作用对量子点的电致发光性能的影响。利用TiO₂作为电子传输/注入层,成功地制备了倒置结构的量子点电致发光器件。通过对单载流子器件电压-电流特性的分析,证明了ITO作为阴极到TiO₂的电子注入特性与Al作为阴极时的效果几乎相同。观察到金属纳米粒子产生的局域等离子体效应提高了器件的效率,使得效率随电流增大而降低的速度明显减小。在电流密度为200 mA/cm²时,电致发光器件的效率大约提高了42%。     

Improved blue quantum dot light-emitting diodes via chlorine passivated ZnO nanoparticle layer

In blue quantum dot light emitting diodes (QLEDs), electron injection is insufficient, which would degrade device efficiency and stability. Herein, we employ chlorine passivated ZnO nanoparticles as electron transport layer to facilitate electron injection into QDs effectively. Moreover, it suppresses exciton quenching at the QD/ZnO interface by blocking charge transfer channel. As a result, the maximum external quantum efficiency of blue QLED was increased from 2.55% to 4.60%, and the operation lifetime of blue QLED was nearly 4 times longer than that of the control device. Our work indicates that election injection plays an important role in blue QLED efficiency and stability.     

Low driving voltage in white organic light-emitting diodes using an interfacial energy barrier free multilayer emitting structure

The driving voltage of white organic light-emitting diodes (WOLEDs) with blue fluorescent and red phosphorescent emitting materials was lowered by using a device architecture with little energy barrier between emitting layers. A mixed layer of hole and electron transport materials was used as a host material and an interlayer, reducing the driving voltage of WOLEDs. The driving voltage of WOLEDs was reduced by more than 4 V and power efficiency of WOLEDs was improved by more than 40% due to little energy barrier for holes and electrons injection in light-emitting layer. In addition, there was little change of electroluminescence spectra from 100 to 10,000 cd/m².     

High efficiency blue phosphorescent organic light-emitting diodes without electron transport layer

High efficiency blue phosphorescent organic light-emitting diodes were fabricated without an electron transport layer using a spirobifluorene based blue triplet host material. The simple blue PHOLEDs without the electron transport layer showed a high external quantum efficiency and current efficiency of 16.1% and 30.2 cd/A, respectively. The high device performances of the electron transport layer free blue PHOLEDs were comparable to those of blue PHOLEDs with the electron transport layer.     

Pure blue and white light electroluminescence in a multilayer organic light-emitting diode using a new blue emitter

We characterized the 6,12-bis{[N-（3,4-dimethylphenyl）-N-（2,4,5-trimethylphenyl）]amino} chrysene （BmPAC）, which has been proven to be a blue fluorescent emission with high EL efficiency. The blue fluorescent device exhibits good performance with an external quantum efficiency of 5.8% and current efficiency of 8.9 cd/A, respectively. Using BmPAC, we also demonstrate a hybrid phosphorescence/fluorescence white organic light-emitting device （WOLED） with high efficiency of 36.3 cd/A. In order to improve the relative intensity of blue light, we plus a blue light-emitting layer （BEML） in front of the orange light emitting layer （YEML） to take advantage of the excess singlet excitons. With the new emitting layer of BEML/YEML/BEML, we demonstrate the fluorescence/phosphorescence/fluorescence WOLED exhibits good performance with a current efficiency of 47 cd/A and an enhanced relative intensity of blue light.     

发光区插入超薄LiF层对有机电致发光器件性能的影响

着重对比了在以DCM掺杂Alq₃为发光层的红光器件的发光区插入超薄LiF层后器件性能的改善。插入超薄LiF层后,器件的最大工作电流密度为487 mA/cm²,相应的最大电致发光亮度为76 740 cd/m²,最大外量子效率为5.9%。器件内量子效率为40%,超过了基于有机荧光小分子发光材料的有机电致发光器件的内量子效率的理论极限值25%。对器件内单线态及三线态激子的形成过程进行了分析,并推测:超薄LiF层的插入提高了器件内单线态电荷转移态/三线态电荷转移态的形成比例,进而提高了器件内单线态激子在激子总数中的比例,最终提高了器件的内量子效率。同时,超薄LiF层的插入改变了发光层内局域的内部电场,使器件的外量子效率不仅没有随电流密度的增加而降低,反而非线性增加。     

基于mCP与UGH2为母体的双发光层高效率蓝色磷光OLED

以9,9'-(1,3-苯基)二-9H-咔唑(m CP)和1,4-二(三苯甲硅烷基)苯(UGH2)为母体,将常用的蓝光染料二(3,5-二氟-2-(2-吡啶)苯基-(2-吡啶甲酸根))合铱(Ⅲ)(FIrpic)掺入这两种母体材料中,制得具有双发光层结构的蓝色磷光有机电致发光器件,并对整个物理机制进行了阐述。该器件较基于m CP或UGH2为母体的单发光层器件有着更高的器件效率。器件的最大电流效率、功率效率、外量子效率分别为21.13 cd/A、14.97 lm/W、10.56%。器件亮度从100 cd/m2到3 000 cd/m2时,效率滚降为34.2%。     

Effect of ethanolamine passivation of ZnO nanoparticles in quantum dot light emitting diode structure

The aging of ZnO nanoparticles in quantum dot light-emitting diode (QD-LED) structures was studied. Coarsening of as-synthesized ZnO nanoparticles is observed in both solution and thin film structures, which potentially deteriorates the performance of QD-LED devices over time. First, the temperature effect on ZnO coarsening was investigated, and it was revealed that aging of ZnO nanoparticles is faster at higher temperature due to a diffusion-controlled mechanism of nanoparticle coarsening. To observe aggregation of ZnO in the film state, the electron transporting part (ZnO/Al) of the QD-LED structure was prepared. The current density of a ZnO film and an electron-only device (QD/ZnO between two electrodes) was also measured. Resistance of the film increased as a function of aging time, which corresponded with observations of the ZnO film by optical microscopy. Aggregation of ZnO nanoparticles was directly measured by the root-mean-square value using atomic force microscopy. Ethanolamine (EA) stabilizer was added to the ZnO solution to disperse the ZnO nanoparticles without aggregation. The effect of EA on the surface passivation of the ZnO found to suppress pinhole formation, as revealed by scanning electron microscopy observations. Finally, the device lifetime was measured for QD-LEDs with EA-stabilized ZnO to understand the effect of ZnO aging on long-term QD-LED device operation.     

聚合物级联发光器件

基于溶液加工方法制备了聚乙撑二氧噻吩-聚(苯乙烯磺酸盐)(PEDOT∶PSS)/氧化锌(ZnO)/乙氧基化聚乙烯亚胺(PEIE)电荷产生层的聚合物级联发光器件, 发现PEDOT∶PSS层电导和厚度对器件的电流-电压特性影响较小, 不同PEDOT∶PSS对器件发光效率的影响主要来自于其对发光层激子不同的猝灭作用, PEDOT∶PSS厚度为60 nm的级联器件比PEDOT∶PSS 厚度为30 nm的级联器件的发光效率稍高, 原因是PEDOT∶PSS较厚时, 其表面形貌更均匀。级联器件的发光效率和驱动电压分别与发光子单元的发光效率和驱动电压之和相近, 说明在较低的电压下电荷产生层就能够有效产生电荷并注入到发光子单元中,级联器件的发光光谱中包含两个发光子单元的发光光谱,说明两个发光子单元在级联器件中都能正常工作。通过对电荷产生层的电容-电压(C-V)特性的测试, 确认了在电荷产生层中存在电荷的积累过程。证明了PEDOT∶PSS/ZnO/PEIE为有效的电荷产生层。首次报道了包含三个SY-PPV发光单元的级联器件, 三个发光子单元发光效率之和与级联器件的发光效率相当, 其最大发光效率和最大外量子效率分别为21.7 cd·A-1和6.95%。在器件亮度为5 000 cd·m-2时, 器件的发光效率和外量子效率分别为20.5 cd·A-1和6.6%。说明并没有由于发光子单元数目增加而影响级联器件的发光效率。并且其发光光谱和发光子单元的发光光谱相接近。通过 进一步降低CGL中空穴注入层对级联器件的影响有望提高级联器件的发光效率。     

新型双色有机电致磷光器件

所研究的有机电致磷光发光器件(OLED)选用了一种新型金属铱的化合物Ir(C6)₂(acac),这种金属化合物由配位体香豆素C6和乙酰丙酮(acac)与金属铱化合形成。Ir(C6)₂(acac)可同时作为电子传输材料和发光掺杂剂。比较香豆素C6和Ir(C6)₂(acac)固体材料的光致发光谱,可见Ir(C6)₂(acac)明显抑制了有机电致发光材料分子与分子之间的发光猝灭效应。采用ITO/TPD(N,N′-diphenyl-N,N′-bis(3-methyl-phenyl)-1,1′biphenyl-4,4′diamine)/Ir(C6)₂(acac)/BAlq(bis(2-methyl-8-quinolinolato-N₁,O₈)-(1,1′-biphenyl-4-olato)aluminum)/Alq₃aluminum/Liq(8-hydroxyquinolinelithium)/Al结构,可得到CIE(Commission Interationaled′Eclairage)值为x=0.43;y=0.40的橙红色发光器件,最高亮度可达3390cd/m₂,最大电流效率为1.3cd/A。采用同样的器件结构以Ir(C6)₂(acac)掺杂Alq₃主体得到绿色发光器件,发光色的CIE坐标值为x=0.29;y=0.58,最高亮度可达8832cd/m₂,最大电流效率为5.6cd/A。器件的发光机理研究表明Ir(C6)₂(acac)的非掺杂器件发光以Ir(C6)₂(acac)的三线态磷光为主,器件发光为橙色;在Alq₃中的单掺杂器件以Alq₃和Ir(C6)₂(acac)的荧光为主,同时有小比例Ir(C6)₂(acac)的三线态磷光成分存在,器件总体发光为绿色。     

High power efficiency in single layer blue phosphorescent organic light-emitting diodes

High efficiency single layer blue phosphorescent organic light-emitting diodes (PHOLEDs) without any charge transport layer were developed. A mixed host of spirobifluorene based phosphine oxide (SPPO13) and 1, 1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) was used as the host in the emitting layer. A high maximum external quantum efficiency of 15.8% and a quantum efficiency of 8.6% at 1000 cd/m² were achieved in the single-layer blue PHOLEDs without any charge transport layer. The maximum power efficiency and power efficiency at 1000 cd/m² were 31.4 and 16.9 lm/W, respectively.     

氧化锌锡作为电子传输层的量子点发光二极管

本文研究了以胶状量子点作为发光层和有机/无机混合材料作 为电子-空穴传输层的电致发光二极管器件. CdSe 量子点以薄膜的形式夹在无机氧化锌锡电子传输层和有机TPD空穴传输层中间构成三明治结构. 氧化锌锡电子传输层采用磁控溅射实现, 有机TPD空穴传输层和量子点发光层则采用旋涂的方法制备, 得到的QD-LEDs器件结构界面陡峭、表面平整. 光电特性表征结果显示器件的电致发光具有良好的单色性、低的开启电压, 利 用具有高电子迁移率和低载流子浓度的无机氧化锌锡薄膜作为电子传输层可 以实现器件在大气环境下稳定、明亮的电致发光. 本文分析了器件的工作机理并通过改变氧化锌锡的电导率达到控制器件中电子和空穴的注入比的目的, 优化了器件的光电性能. 关键词： 量子点 氧化锌锡 电致发光 电子传输层     

Control of device performances of phosphorescent white organic light-emitting diodes by managing charge transport properties of host materials

Interlayer-free phosphorescent white organic light-emitting diodes (PHWOLEDs) with a mixed-host emitting structure in red emitting layer were developed and device performances were investigated according to the host composition in the red emitting layer. Device performances could be effectively managed by a simple change of host materials in the red emitting layer. A high quantum efficiency was obtained in PHWOLEDs with electron transport-type host in the red emitting layer and red emission was strong in PHWOLEDs with mixed-host in the red emitting layer. In addition, stable color performances were obtained in electron transport-type host rich devices.     

纳米结构氧化镍缓冲层对蓝色有机发光二极管性能的影响

在阳极和空穴传输层分别引入氧化镍纳米结构缓冲层,制备了蓝色有机发光二极管,对二极管的电学和光学特性进行了测试分析,研究了采用电化学方法制备的氧化镍纳米结构对器件的影响.结果表明,纳米结构氧化镍缓冲层能够有效地提高空穴-电子对的产生和复合效率,它的引入带来了高效的空穴注入及发光层中的载流子平衡,能有效提高有机发光二极管的电致发光特性.氧化镍缓冲层沉积时间为30 s的器件具有最高的亮度和电流效率,分别为42 460 cd/m2和24 cd/A,该器件的CIEx,y 色坐标为(0.212 9,0.325 2).     

Enhancement of Frster energy transfer from thermally activated delayed fluorophores layer to ultrathin phosphor layer for high color stability in non-doped hybrid white organic light-emitting devices

Fluorescence/phosphorescence hybrid white organic light-emitting devices(WOLEDs) based on double emitting layers(EMLs) with high color stability are fabricated.The simplified EMLs consist of a non-doped blue thermally activated delayed fluorescence(TADF) layer using 9,9-dimethyl-9,10-dihydroacridine-diphenylsulfone(DMAC-DPS) and an ultrathin non-doped yellow phosphorescence layer employing bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2']iridium(acetylacetonate)((tbt)_2Ir(acac)).Two kinds of materials of 4,7-diphenyl-1,10-phenanthroline(Bphen) and 1,3,5-tris(2-Nphenylbenzimidazolyl) benzene(TPBi) are selected as the electron transporting layer(ETL),and the thickness of yellow EML is adjusted to optimize device performance.The device based on a 0.3-nm-thick yellow EML and Bphen exhibits high color stability with a slight Commission International de l'Eclairage(CIE) coordinates variation of(0.017,0.009) at a luminance ranging from 52 cd/m~2 to 6998 cd/m~2.The TPBi-based device yields a high efficiency with a maximum external quantum efficiency(EQE),current efficiency,and power efficiency of 10%,21.1 cd/A,and 21.3 lm/W,respectively.The ultrathin yellow EML suppresses hole trapping and short-radius Dexter energy transfer,so that Forster energy transfer(FRET)from DMAC-DPS to(tbt)_2Ir(acac) is dominant,which is beneficial to keep the color stable.The employment of TPBi with higher triplet excited state effectively alleviates the triplet exciton quenching by ETL to improve device efficiency.     

Quantum Dot Research: Current State and Future Prospects

This article reviews the current state of research involving semiconductor quantum dots, provides a brief review of the theory behind their unique properties, and an introduction explaining the importance of quantum dot research. The characteristic shifting of the band gap energy with quantum dot size, as predicted from the density of states for low-dimensional structures, allows experimental measurements to determine the extent to which quantum confinement effects play a role in the resulting properties. A few of the current techniques used to measure the presence and physical characteristics of quantum dots and their energy levels is reviewed, including transmission electron microscopy, optical transmission, and Raman and photoluminescence spectroscopy. Finally, some of the more exciting applications for quantum dots currently being researched for use in the field of optoelectronics are reviewed, including quantum dot infrared photodetectors, quantum dot lasers, and quantum dot solar cells. Comments are made on the current progress and the future prospects of quantum dot research and device applications.     

Organic light-emitting diode with an emitter based on a planar layer of CdSe semiconductor nanoplatelets

Colloidal CdSe semiconductor nanoplatelets with characteristic longitudinal sizes of 20–70 nm and thicknesses of several atomic layers are synthesized. The spectra and kinetics of the photoluminescence of these quasi-two-dimensional nanostructures (quantum wells) at room and cryogenic temperatures are investigated. A hybrid light-emitting diode with the electron and hole transport layers based on TAZ and TPD organic compounds, respectively, and the active “emissive” element based on a layer of such single-component nanoplatelets is designed. The spectral and electrical characteristics of the fabricated device, emitting at a wavelength of λ = 515 nm, are determined. The use of quasi-two-dimensional nanostructures of this kind (nanoplatelets) is promising for the fabrication of hybrid light-emitting diodes with pure colors.     

基于超薄发光层及双极性混合间隔层的白光有机发光器件研究

本文采用非掺杂超薄发光层及双极性混合间隔层结构,获得了高效、光谱稳定的白光有机发光器件.基于单载流子器件及单色蓝光有机发光器件的研究,确定了双极性混合间隔层的最佳比例;通过瞬态光致发光寿命研究,验证了不同发光材料之间的能量传递过程;得到的三波段和四波段白光有机发光器件的最高效率分别为52 cd/A (53.5 lm/W)和13.8 cd/A (13.6 lm/W),最高外量子效率分别为17.1%和11.2%.由于发光层不同颜色之间依次的能量传递结构,三波段白光有机发光器件的亮度从465到15950 cd/m~2时,色度坐标的变化?CIE仅为(0.005, 0.001);四波段白光有机发光器件的亮度从5077到14390 cd/m~2时,色度坐标的变化?CIE为(0.023, 0.012).