Efficient top-emitting white organic light emitting device with an extremely stable chromaticity and viewing-angle

In this paper,we report on the fabrication of a top-emitting electrophosphorescent p-i-n white organic lightemitting diode on the basis of a low-reflectivity Sm/Ag semi-transparent cathode together with a thickness-optimized ZnS out-coupling layer.With a 24-nm out-coupling layer,the reflectivity of the cathode is reduced to 8% at 492 nm and the mean reflectivity is 24% in the visible area.By introducing an efficient electron blocking layer tris（1phenylpyrazolato,N,C2 ＇）iridium（III）（Ir（ppz） 3） to confine the exciton recombination area,the current efficiency and the colour stability of the device are effectively improved.A white emission with the Ir（ppz） 3 layer exhibits a maximum current efficiency of 9.8 cd/A at 8 V,and the Commission Internationale de L＇Eclairage（CIE） chromaticity coordinates are almost constant during a large voltage change of 6 V-11 V.There is almost no viewing angular dependence in the spectrum when the viewing angle is no more than 45,with a CIE x,y coordinate variation of only（±0.0025,±0.0008）.Even at a large viewing angle（75）,the CIE x,y coordinate change is as small as（±0.0087,±0.0013）.

High-contrast top-emitting organic light-emitting devices

In this paper we report on a high-contrast top-emitting organic light-emitting device utilizing a moderate-reflection contrast-enhancement stack and a high refractive index anti-reflection layer.The contrast-enhancement stack consists of a thin metal anode layer,a dielectric bilayer,and a thick metal underlayer.The resulting device,with the optimized contrast-enhancement stack thicknesses of Ni（30 nm）/MgF 2（62 nm）/ZnS（16 nm）/Ni（20 nm） and the 25-nm-thick ZnS anti-reflection layer,achieves a luminous reflectance of 4.01% in the visible region and a maximum current efficiency of 0.99 cd/A（at 62.3 mA/cm 2） together with a very stable chromaticity.The contrast ratio reaches 561：1 at an on-state brightness of 1000 cd/m^2 under an ambient illumination of 140 lx.In addition,the anti-reflection layer can also enhance the transmissivity of the cathode and improve light out-coupling by the effective restraint of microcavity effects.

White Organic Light Emitting Devices Based on Multiple Emissive Nanolayers

In this paper,a white organic light-emitting device(WOLEDs) with multiple-emissive-layer structure has been fabricated.The device has a simple structure of indium tin oxide(ITO)/NPB(20 nm)//DPVBi(20 nm)/CDBP:x Ir(btp)2acac(10 nm)/Alq3(25 nm)/BCP(5 nm)/Cs F(1 nm)/Al(150 nm)(x= 0.15,2.5 and 3.0 wt%),where NPB and BCP are used as the hole-injecting layer,electron transporting and hole blocking layer,respectively.White light emission was realized in an OLED with 2.5% Ir(btp)2acac doping concentration.The device exhibits peak efficiency of 1.93 cd/A at 9 V and maximum brightness of 7005 cd/m^2 at 14 V.The Commission International de I'Eclairage(CIE)(1931) coordinates of white emission are well within the white zone,which moves from(0.35,0.33) to(0.26,0.30) when the applied voltage is varied from 5 V to 14 V.

Enhancement of Frster 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.

Top-Emitting White Organic Light-Emitting Diodes Based on Cu as Both Anode and Cathode

It is still challenging to obtain broadband emission covering visible light spectrum as much as possible with negligible angular dependence. In this work, we demonstrate a low driving voltage top-emitting white organic light-emitting diode （TEWOLED） based on complementary blue and yellow phosphor emitters with negligible angular dependence. The bottom copper anode with medium reflectance, which is compatible with the standard complementary metal oxide semiconductor （CMOS） technology below 0.13 μm, and the semitransparent multi- layer Cs2CO3/AI/Cu cathode as a top electrode, are introduced to realize high-performance TEWOLED. Our TEWOLED achieves high efficiencies of 15.4callA and 12.1 1m/W at a practical brightness of lO00cd/m2 at low voltage of 4 V.

Examining micro-cavity parameters of top emission organic light-emitting diode with low-order resonant modes

Emission characteristics of top emitting organic light-emitting devices （TOLEDs） with Ag as reflective anode, Al/Ag as semitransparent cathode and 90 160 nm [N-（1-naphthyl）-N-phenyl-amino] biphenyl/tris-（8-hydroxy quinoline） aluminum （NPB/Alq3） sandwiched in the electrodes are examined. The electroluminescence （EL） spectra of the TOLEDs are simulated based on the Fabry-Perot cavity theory. And the resonant modes in cavity structure of TOLEDs is discussed and clarified which can accurately describe the work principle of the devices. A fairly good match between calculated values and experimental data is achieved at different emission colors from bluish green to orange.

White organic light-emitting devices fabricated by spin-coating molecular materials

White organic light-emitting device (WOLEDs) employing molecular mixed host (MH) is demonstrated by spin-coating.The spin-coated film functions as light-emitting layer and hole transporting layer,with the former formed by spin-coating solution containing MH of NPB (N.N'-Bis(naphthalene-1-yl)-N,N'-bis(phenyl)-benzidine) and MADN (2-methyl-9,10-di(2-naphthyl) anthracene),blue dye (4,4'-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl) and yellow dye (5,6,11,12-tetraphenylnaphacene).The performances of the devices made with different mixed ratio of MH are investigated.It is found that the device performances depends on the MH ratio,and under the optimal NPB:MADN ratio (60:40),the WOLEDs show a maximum luminance of 24 671 cd/m2 and a current efficiency of 5.8 cd/A for the practical luminance of 1000 cd/m2.The effect of MH ratio on device performances can be attributed to the difference of hole mobility between the NPB and MADN.

Highly Efficient White Organic Light-emitting Devices with Optimized Electron Transporting Layers

We fabricated three phosphorescent blue organic light-emitting devices based on blue phosphor of iri-dium（Ⅲ） bis[（4,6-difluorophenyl）-pyridinato-N,C2＇]（Firpic） with different electron transporting layer（ETL） materialsBy analyzing efficiency curves and spectral characteristics, the significant effect of ETL on many aspects of deviceperformance was demonstrated. With optimized ETL, the characteristics of devices, such as voltage and efficiencywere significantly improved. Combined with a yellow phosphor of iridium（Ⅲ） bis（4-phenylthieno[3,2-c]pyridinato-N,C2＇） acetylacetonate（PO-01）, phosphorescent white organic light-emitting devices（PhWOLEDs） were obtained.Then, with an aim to promote the performance of the PhWOLEDs~ a thin layer of 4,4＇,4＂-tri（N-carbazolyl）-triphenylamine（TCTA） was introduced between two light emission layers, and the diffusion of excitons was confined.The outperformance device fabricated with 4,7-diphenyl-l,10-phenanthroline（Bphen） as the electron transportinglayer exhibited a peak current efficiency of 36.6 cd/A, a peak power efficiency of 19.2 lm/W, and the InternationalCommission on Illumination coordinates（0.37, 0.46）.

Blue emitting exciplex for yellow and white organic light‑emitting diodes

White organic light-emitting diodes(WOLEDs)have several desirable features,but their commercialization is hindered by the poor stability of blue light emitters and high production costs due to complicated device structures.Herein,we investigate a standard blue emitting hole transporting material(HTM)N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine(NPB)and its exciplex emission upon combining with a suitable electron transporting material(ETM),3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole(TAZ).Blue and yellow OLEDs with simple device structures are developed by using a blend layer,NPB:TAZ,as a blue emitter as well as a host for yellow phosphorescent dopant iridium(III)bis(4-phenylthieno[3,2-c]pyridinato-N,C2')acetylacetonate(PO-01).Strategic device design then exploits the ambipolar charge transport properties of tetracene as a spacer layer to connect these blue and yellow emitting units.The tetracene-linked device demonstrates more promising results compared to those using a conventional charge generation layer(CGL).Judicious choice of the spacer prevents exciton difusion from the blue emitter unit,yet facilitates charge carrier transport to the yellow emitter unit to enable additional exciplex formation.This complementary behavior of the spacer improves the blue emission properties concomitantly yielding reasonable yellow emission.The overall white light emission properties are enhanced,achieving CIE coordinates(0.36,0.39)and color temperature(4643 K)similar to daylight.Employing intermolecular exciplex emission in OLEDs simplifes the device architecture via its dual functionality as a host and as an emitter.

Highly Efficient Hybrid White Tandem Organic Light-Emitting Diodes with MoO3 Layer

Electroluminescence （EL） characteristics have been studied for a hybrid tandem white organic light emitting diode （OLED） with a blue emitting fluorescent EL1 unit based on BCzVBi and a yellow emitting phosphorescent EL2 unit based on （fbi）2Ir（acac）, where a MoO3 layer is inserted between EL1 and EL2 units as charge generation layer （CGL）. Maximum current and power efficiencies of 68.1 cd/A and 29.2 lm/W were obtained, respectively, while the current and power efficiencies at luminance of 1000 cd/m2 were 68.0 cd/A and 24.6 lm/W. The yellow emission appears from about 4.5 V firstly, while the blue emission starts to appear from about 5.4 V. It was found that charge generation from CGL of MoO3/NPB bilayer occurred at high voltages of above 5.4 V but not at low voltages below 5.2 V.

一种白光有机电致发光器件的制备

通过对器件结构的优化设计,提高了白光电致发光器件中蓝光成分的发光效率,从而得到了一种较为理想的有机白光电致发光器件。驱动电压为5V时,电流密度J=0 5mA/cm2,器件的效率达到最大,流明效率为1 92lm/W,此时器件的发光亮度接近20cd/m2,色坐标为(x=0 317,y=0 328),非常接近白光等能点,是色度很好的白光。并且在很大范围内,色度随器件的驱动电压或电流变化不大,当驱动电压变化至15V时,J=232mA/cm2,色坐标变化至(x=0 338,y=0 353)。在电压为22V时,器件的亮度达到最大,为17000cd/m2。此外器件结构相对简单,器件制备的可重复性得到很大程度的改善。

微腔有机电致发光白光器件设计及制作

用一种宽谱带材料Alq3作为发光层,设计并制作白色有机微腔电致发光器件。器件结构:Glass/DBR/ITO(194nm)/NPB(93nm)/Alq3(49nm)/MgAg(150nm),得到了位于蓝(488nm)和红(612nm)光区域的两个腔发射模式,并通过颜色匹配获得了白光。器件的最大电致发光亮度16435cd/m2,最大效率11.1cd/A,典型亮度值100cd/m2时的发光效率、电压、电流密度分别是9cd/A,6V和1.2mA/cm2,CIE色坐标为(0.32,0.34)。在不同的驱动电压下,器件的发光颜色稳定,说明了微腔是一种制作白光OLED的有效结构。

基于rubrene掺杂剂的高亮度白色有机电致发光器件

采用CBP主体材料中掺杂rubrene，制备了结构为ITO／2T-NATA（25nm）／NPBX（20nm）／CBP：1％rubrene（10nm）／NPBX（5nm）／DPVBi（30nm）／TPBi（20nm）／Alq（10nm）／LiF（1nm）／Al的白光器件，此结构将器件的发光区控制在了DPVBi层和rubrene掺杂层。利用rubrene染料本身的载流子俘获空穴特性与CBP母体转移来的能量发射荧光特性，以及插入的5nm NPBX的电子阻挡特性获得了高亮度的白光器件。此器件在驱动电压为16V时最大亮度达到25110cd／m^2，对应的色坐标为（0．30，0．34），在驱动电压为10V时最大电流效率为5．32cd／A，外量子效率为1．65％。而且，驱动电压在10～16V时，即达到最大亮度和最大效率时，其色坐标都在白光等能点（0．33，0．33）附近。

高色纯度有机白光电致发光器件

介绍了具有高色纯度的多层有机白光器件,器件发光的色坐标为x=0.33,y=0.34,非常接近白光等能点,是色度很好的白光器件。而且在8～14V很大的范围内,发光色度随器件的驱动电压或电流的变化不大,基本稳定在x=0.33,y=0.34。在电压为19V时,器件的亮度达到了最大9735cd/m2,在电压为9V时,器件的效率达到了最大4.5cd/A。

稳定的蓝色及白色有机薄膜电致发光器件

报道了一种稳定的蓝色和白色有机薄膜电致发光器件 ,蓝色器件最大亮度为 75 2 6cd/m2 ,最大效率1 45lm/W ,半亮度寿命 10 35h(初始亮度 10 0cd/m2 )。白色器件的最大亮度为 1485 0cd/m2 ,最大效率2 88lm/W ,色度x =0 31,y =0 38,且色度不随电流增大而变化 ,半亮度寿命为 2 86 0h(初始亮度 10 0cd/m2 )。

白光有机发光二极管的研究进展

由于白光有机发光二极管(WOLED)具有效率高、亮度高、功耗低、视角广、响应速度快、主动发光、超薄超轻以及可柔性化等优异性能,并在显示和照明领域有广阔的应用前景,受到学者和业界的广泛重视而成为研究热点.本文首先介绍了实现WOLED的不同方法,然后从发光材料种类的角度,阐述了全荧光WOLED、全磷光WOLED、基于荧光/磷光杂化WOLED以及延迟荧光WOLED近年来的研究进展,并结合我们研究团队最近的工作详细地介绍了不同高性能WOLED的器件结构、设计思想、工作原理、物理机制以及发光过程;接着,简单介绍了柔性WOLED最近研究进展;最后探讨了WOLED目前存在的问题及其未来的发展趋势.

利用复合色彩转换膜实现白色有机电致发光

利用蓝色有机发光二极管激发荧光色彩转换膜的方法,制备了一种新型的白色有机电致发光器件.蓝色有机发光二极管的发光层采用在4,4′-Bis(carbazol-9-yl)biphenyl(CBP)主体中掺杂高效蓝色荧光染料N-(4-((E)-2-(6-((E)-4-(diphenylamino)styryl)naphthalen-2-yl)vinyl)phenyl)-N-phenylbenzenamine(N-BDAVBi)来制备.有机/无机复合色彩转换膜是将有机荧光颜料VQ-D25和无机荧光粉钇铝石榴石(YAG)按一定的重量比均匀分散到-[CH3CH2COOCH3]n-(PMMA)中经涂敷、固化而成.通过与单纯有机或无机色彩转换膜的比较及调整复合转换膜本身的厚度和荧光颜料的掺杂比例来优化白光器件的发光光谱,获得了色稳定性较高的白色有机电致发光器件.当驱动电压由6V升至14V时,器件的色坐标仅在(0.354,0.304)和(0.357,0.312)之间变化,其最高电流效率约为5.8cd/A(4.35mA/cm2),最高亮度为16800cd/m2(14V).

有机电致发光白光器件的研究进展

在十多年的时间里 ,有机电致发光二极管 (OrganicLight emittingDiodes,OLEDs)的研究和应用取得了长足的进展。有机电致发光器件具有许多优点 ,例如 :自发光、视角宽、响应快、发光效率高、温度适应性好、生产工艺简单、驱动电压低、能耗低、成本低等 ,因此有机电致发光器件极有可能成为下一代的平板显示终端。有机电致发光白光器件因为可以用于全彩色显示和照明 ,已成为OLED研究中的热点。介绍了有机电致发光白光器件的研究进展 ,按发光的性质将白光器件分为荧光器件和磷光器件两类 ,按发光层数将白光器件分为单层和多层器件 ,对相关材料、器件结构。

间隔层对双发光层白色有机电致发光器件性能的影响

采用蓝色bis[3,5-difluoro-2-(2-pridyl)phenyl-(2-carboxypyribyl)iridumⅢ](FIrpic)和黄色bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2']iridium(acetylacetonate)[(t-bt)2Ir(acac)]两种磷光染料,制备了双发光层结构的白色有机电致发光器件,器件结构为ITO/TAPC(30 nm)/host:(t-bt)2Ir(acac)[(10-x)nm,4%]/spacer(x nm)/host:FIrpic(15 nm,8%)/Bphen(40 nm)/Mg∶Ag(200 nm)。分别选用p型1,1-bis[(di-4-tolylamino)phenyl]cyclohexane(TAPC)和n型tris[3-(3-pyridyl)-mesityl]borane(3TPYMB)作为主体材料制备了两种类型的器件,通过在两个发光层之间加入一层较薄的间隔层进行器件优化。结果表明,加入间隔层之后,器件性能得到提高,获得了色稳定性较好的白光器件。当主体为TAPC时,使用间隔层后器件取得最大亮度为19 550 cd/m2,最大电流效率为8.3 cd/A;当主体为3TPYMB时,使用间隔层后器件的最大亮度为1 950 cd/m2,最大电流效率为30.7 cd/A。实验结果表明,器件性能的提高,是由于加入了间隔层之后载流子复合区域拓宽,促进了发光层中电子和空穴的平衡。

白色有机薄膜电致发光

White color emitting organic electroluminescence (EL) device is a convenient means to realize full-color display because the three necessary primary colors could be obtained by color filters from white back light. In this paper a new three-layer device is presented. We used N, N′-bis-(lnaphhyl)-N , N′-diphenyl-1, 1′-biphenyl-4, 4′-diamine (NPB) as the hole transport layer, Alq as the electron transport layer, CuPc as the buffer layer, and TPBi as the blocking layer inserted between NPB and Alq.The 5,6,11,12-tetraphenyltetracene (Rubrene) as dopant was doped into the blocking layer.\;It was thought initially that if energy transfer existed between the host and dopant in photoluminescence (PL) of NPB doped with Rubrene, white emission might be obtained in a device such as ITO/CuPc/NPB:Rubrene/TPBi/Alq/Mg:Ag. Thus the PL of NPB:Rubrene system excited by NPB absorption band with different dopant concentrations were investigated in advance. There are two bands in the PL spectra, the blue one is emitted by NPB and the yellow one is by Rubrene. The ratio of these two bands can be adjusted by changing the Rubrene concentration. This shows that energy transfer does occur from NPB to Rubrene. Time-resolved spectra of this system, which will be given in another paper, confirm further that the energy transfer exists and is quite effective. White emission can be produced by adjusting the concentration of Rubrene in PL. However, devices of structure ITO/CuPc/NPB:Rubrene/TPBi/Alq/Mg:Ag were made according to these results with TPBi as the blocking layer, white emission can not be obtained by changing the Rubrene concentration.\;For another device of structure ITO/CuPc/NPB/TPBi:Rubrene/Alq/Mg : Ag, with a blocking layer TPBi doped by Rubrene concentration 1.5% inserted between NPB and Alq, white emission can be obtained. The highest luminance and maximum efficiency are 8635cd/m 2 and 1.39lm/W respectively , CIE coordinate x =0.31, y =0.32. The color of the emitted light can still be optimized by adjusting the relative thickness of the relevant layers and dopant concentration.\;The electroluminescence mechanism of two kinds of cells was discussed.