Efficient white organic light-emitting devices using 4,7-diphenyl-1,10-phenanthroline as block layer

A white light-emitting device has been fabricated with a structure of ITO/m-MTDATA (45 nm)/NPB (10 nm)/DPVBi (8 nm)/DPVBi:DCJTB 0.5% (15 nm)/BPhen (x nm)/Alq₃ [(55−x) nm]/LiF (1 nm)/Al, with x=0, 4, and 7. BPhen was used as the hole-blocking layer. This results in a mixture of lights from DPVBi molecules (blue-light) and DCJTB (yellow-light) molecules, producing white light emission. The chromaticity can be readily adjusted by only varying the thickness of the BPhen layer. The CIE coordinates of the device are largely insensitive to the driving voltages. When the thickness of BPhen is 7 nm, the device exhibits peak efficiency of 6.87 cd/A (3.59 lm/W) at the applied voltage of 6 V, the maximum external quantum efficiency η_ext=2.07% corresponding to 6.18 cd/A, and the maximum brightness is 18494 cd/m² at 15 V.     

彩色有机薄膜电致发光及动态矩阵显示

研究了绿色、红色、蓝色和白色4种有机薄膜电致发光器件.通过掺杂得到了高稳定性的绿色及红色器件,绿色器件的半寿命达14000小时(初始亮度100cd/m²),红色器件的半寿命为7500小时(初始亮度50cd/m²).还研究了具有空穴锁定层及非锁定层的多种不同结构和材料的蓝色及白色器件.研究表明无论蓝色还是白色器件,具有空穴锁定层的器件稳定性较差,老化过程中界面势垒的变化很大.非锁定层的蓝色及白色器件中,新材料JBEM比DPVBi有更优越的性能.JBEM构成的蓝色器件的半亮度寿命为1035小时(初始亮度100cd/m²).由JBEM构成的白色器件中,由蓝色及红色掺杂在同一层的器件得到最好的稳定性,其半亮度寿命为2800小时(初始亮度100cd/m²),而且它具有发光颜色不随电流变化而变化的特点.在稳定性改善的基础上研制成功96×60线,分辨率为2线/mm的绿色及白色矩阵显示屏,还利用选择蒸发的方法制造了彩色矩阵屏,设计和研制了驱动及控制电路,实现了动态显示.     

Non-doped red to yellow organic light-emitting diodes with an ultrathin 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) layer

In this letter, bright non-doped red to yellow organic light-emitting diodes (OLEDs) with ultrathin 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) layer as the emitting layer were fabricated. It was investigated that the effect of the ultrathin DCJTB layer on the electroluminescent (EL) performance of OLEDs. The DCJTB layer was incorporated at different positions in the conventional tris(8-quinolinolato)-aluminum (AlQ)-based devices (ITO/NPB/AlQ/LiF/Al). The emission of DCJTB was dominative in the EL spectra of the devices, in which the position of 0.3 nm DCJTB layer was less than 10 nm from the NPB/AlQ interface. The EL peak emission of DCJTB shifted to blue side as DCJTB position moved gradually from AlQ to NPB layer. The highest brightness of the device with 0.3 nm DCJTB layer inserted into NPB reached 16,200 cd/m² at 15 V, with the CIE coordinates of (0.522, 0.439).     

High efficiency small molecule white organic light-emitting devices with a multilayer structure

In this paper, a new white organic light-emitting device (WOLED) with multilayer structure has been fabricated. The structure of devices is ITO/N, N-bis-(1-naphthyl)-N, N^′-diphenyl-1, 1′-biphenyl-4, 4′-diamine (NPB) (40 nm)/NPB: QAD (1%): DCJTB (1%) (10 nm) /DPVBi (10 nm) /2, 9-dimethyl, 4, 7-diphenyl, 1, 10-phenanthroline (BCP) (d nm)/tris-(8-hydroxyquinoline) aluminium (Alq₃)(50-d nm)/LiF (1 nm)/Al (200 nm). In our devices, a red dye 4-(dicyanomethylene)-2-t-butyl-6 (1, 1, 7, 7-tetramethyl julolidyl-9-enyl)-4H-pyran (DCJTB) and a green dye quinacridone (QAD) were co-doped into NPB. The device with 8 nm BCP shows maximum luminance of 12 852 cd/m² at 20 V. The current efficiency and power efficiency reach 9.37 cd/A at 9 V and 3.60 lm/W at 8 V, respectively. The thickness of the blocking layer permit the tuning of the device spectrum to achieve a balanced white emission with Commission International de’Eclairage (CIE) chromaticity coordinates of (0.33,0.33). The CIE coordinates of device change from (0.3278, 0.3043) at 5 V to (0.3251, 0.2967) at 20 V that are well in the white region, which is largely insensitive to the applied bias.     

以蓝色发光材料DPVBi为基质的白色发光器件

白色有机发光器件是实现彩色平板显示的重要方案之一。利用蓝色发光材料DPVBi[4，4′—(2，2—苯乙烯基)—1，1′—联苯]掺杂红光染料DCJTB[4—氰甲烯基—2—叔丁基—6—(1，1，7，7—四甲基久洛尼定基—9—烯炔基—4H—吡喃)]作发光层制备了白色发光器件。研究了DPVBi掺杂不同浓度IDCJTB薄膜的光致发光性质，根据光致发光结果，制备了以DPVBi掺杂不同浓度DCJTB作发光层的电致发光器件，其结构为ITO／GuPc／NPB／DPVBi：DCJTB／Alq3／LiF／Al。当DCJTB质量分数为0．0008时，器件实现了白色发光(色度x=0．25，y=0．32)，电致发光和光致发光的掺杂比例基本相符，表明器件的白色发光主要是由基质DPVBi向掺杂剂DCJTB的能量传递产生的。研究还发现：白色器件随电压升高，光谱中蓝色成分相对于红色成分的比例略有增加，文章对此现象进行了分析。该白光器件在14V时达到最高亮度7822cd／cm^2，在20mA／cm^2电流密度下的亮度为-489cd／cm^2，最大流明效率为1．75lm／W。     

Co50Fe50-xSix合金的结构相变和磁性

利用实验测量和理论计算相结合的方法,研究了介于B2结构CoFe低有序合金和L2₁结构Co₂FeSi高有序合金之间的Co₅₀Fe_50-xSi_x合金的结构相变、磁相变、分子磁矩和居里温度.采用考虑Coulomb相互作用的广义梯度近似(GGA+U)方法计算了合金的能带结构.研究发现,合金出现较强的原子有序倾向,表现出较强的共价成相作用.合金的晶格常数、磁矩、居里温度随Si含量的增加而线性地降低,极限成分Co₂FeSi合金的分子磁矩和居里温度分别达到5.92μ_B和777 ℃.原子尺寸效应导致合金晶格发生变化,但并未成为居里温度和分子磁矩变化的主导因素.分子磁矩的变化符合Slater-Pauling原理,但发现原子磁矩的变化并非线性,据此提出了共价成相对磁性影响的观点.采用Stearns理论解释了居里温度的变化趋势,排除了原子间距对居里温度的主导影响作用.能带计算的结果还表明,Co₂FeSi作为半金属材料并非十分完美,可能在实际应用中会出现自旋极化率降低的问题.发现该系列合金的结构相变和磁相变随着成分的变化聚集在窄小的成分和温度范围内. 关键词： 磁性 Heusler合金 结构相变     

Optical properties of white organic light-emitting devices fabricated with three primary-color emitters by using organic molecular-beam deposition

White organic light-emitting devices (WOLEDs) with Mg:Ag/Alq₃/Alq₃:DCJTB/Alq₃/DPVBi/α-NPD/ITO and Mg:Ag/Alq₃/DPVBi:DCJTB/Alq₃/DPVBi/α-NPD/ITO structures were fabricated with three primary-color emitters of red, green, and blue by using organic molecular-beam deposition. Electroluminescence spectra showed that the dominant white peak for the WOLEDs fabricated with host red-luminescence Alq₃ and DPVBi layers did not change regardless of variations in the current. The Commission Inernationale de l'Eclairage (CIE) chromaticity coordinates for the two WOLEDs were stable, and the WOLEDs at 40 mA/cm² with luminances of 690 and 710 cd/cm² showed an optimum white CIE chromaticity of (0.33, 0.33). While the luminance yield of the WOLED fabricated with a host red-luminescent Alq₃ emitting layer below 30 mA/cm³ was larger than that of the WOLED fabricated with a DPVBi layer, above 30 mA/cm², the luminance yield of the WOLED fabricated with the DPVBi layer was higher than that of the WOLED with the Alq₃ layer and became more stable with increasing current density. These results indicate that WOLEDs fabricated with a host red-luminescence DPVBi layer without any quenching behavior hold promise for potential applications in backlight sources in full-color displays.     

电子传输层PBD对Alq3：DCJTB电致发光器件的影响

以PBD为电子传输层制作了一组掺杂型有机电致发光器件,并研究了掺杂器件中PBD对器件的光谱、亮度等的影响。发现PBD与NPB和DCJTB分别掺杂的器件的光谱与其它的器件不同,然后运用了载流子的注入、传输及PBD的传输特性等方法对光谱做出了合理的解释,并运用高斯截谱的方法分析了各个发光峰的产生原因。     

有机发光材料DPVBi的空穴阻挡特性

讨论了有机发光材料4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl(DPVBi),在结构为ITO/N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine(NPB)/DPVBi/tris-(8-hydroxyquinoline)aluminum(Alq₃)/LiF/Al的有机电致发光器件中所表现出来的空穴阻挡特性。通过实验可以看到,当NPB的厚度小于DPVBi的厚度时,DPVBi对空穴的阻挡作用和其自身的厚度有关,厚度越大阻挡能力越强。DPVBi的厚度一定(120nm)且不足以将空穴完全限制于DPVBi层内时,其对空穴的阻挡能力,随着NPB厚度(30~60nm)的增加而相对减弱。当NPB的厚度大于DPVBi的厚度时,进入DPVBi层的空穴,随着它们之间厚度差别的增大而增加,从而使器件的光谱半峰全宽加大。这几条规律对于制作基于DPVBi的有机蓝光和有机白光器件具有一定的指导意义。     

空穴注入层对蓝色有机电致发光器件性能的影响

以DPVBi为发光层,NPB为空穴传输层,在阳极ITO和NPB之间分别插入不同的空穴注入层CuPc和PEDOT:PSS,制备了两种结构的蓝色有机电致发光器件(OLEDs):ITO/CuPc/NPB/DPVBi/BCP/Alq3/Al和ITO/PEDOT:PSS/NPB/DPVBi/BCP/Alq3/Al,研究了不同空穴注入材料对蓝色OLEDs发光性能的影响,并与没有空穴注入层的器件进行了比较.其中CuPc分别采用旋涂和真空蒸镀两种丁艺,比较了不同成膜工艺对器件发光特性的影响.结果表明:加入空穴注入层的器件比没有空穴注入层器件性能要好,其中插入水溶性CuPc的器件,其发光亮度和效率虽然比蒸镀CuPc器件要低,但比插入PEDOT:PSS 器件发光性能要好.又由于水溶性CuPc采用旋涂工艺成膜,与传统CuPc相比,制备工艺简单,所以为一种不错的空穴注入材料.     

Electrical characteristics and efficiency of organic light-emitting diodes depending on hole-injection layer

In a device structure of ITO/hole-injection layer/N,N′-biphenyl-N,N′-bis-(1-naphenyl)-[1,1′-biphthyl]4,4′-diamine(NPB)/tris(8-hydroxyquinoline)aluminum(Alq₃)/Al, we investigated the effect of the hole-injection layer on the electrical characteristics and external quantum efficiency of organic light-emitting diodes. Thermal evaporation was performed to make a thickness of NPB layer with a rate of 0.5–1.0 Å/s at a base pressure of 5 × 10⁻⁶ Torr. We measured current–voltage characteristics and external quantum efficiency with a thickness variation of the hole-injection layer. CuPc and PVK buffer layers improve the performance of the device in several aspects, such as good mechanical junction, reducing the operating voltage, and energy band adjustment. Compared with devices without a hole-injection layer, we found that the optimal thickness of NPB was 20 nm in the device structure of ITO/NPB/Alq₃/Al. By using a CuPc or PVK buffer layer, the external quantum efficiencies of the devices were improved by 28.9% and 51.3%, respectively.     

The roles of zinc selenide sandwiched between organic layers and its applications in white light-emitting diodes

In this paper, the roles of zinc selenide (ZnSe) sandwiched between organic layers, i.e. organic/ZnSe/aluminum quinoline (Alq₃), have been studied by varying device structure. A broad band emission was observed from ITO/poly(N-vinylcarbazole)(PVK)(80 nm)/ZnSe(120 nm)/ Alq₃(15 nm)/Al under electric fields and it combined the emissions from the bulk of PVK, ZnSe and Alq₃, however, emission from only Alq₃ was observed from trilayer device ITO/N,N^′-bis-(1-naphthyl)-N,N^′-diphenyl-1, 1^′-biphenyl-4, 4^′-diamine (NPB) (40 nm)/ZnSe(120 nm)/ Alq₃(15 nm)/Al. Consequently the luminescence mechanism in the ZnSe layer is suggested to be charge carrier injection and recombination. By thermal co-evaporating Alq₃ and 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB), we get white light emission with a Commission Internationale de l’E clairage (C.I.E) co-ordinates of (0.32, 0.38) from device ITO/PVK(80 nm)/ZnSe(120 nm)/ Alq₃:DCJTB(0.5 wt% DCJTB)(15 nm)/Al at 15 V and the device performs stably with increasing applied voltages.     

Color-tunable organic light-emitting devices using a thin N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine layer at heterojunction interface

Novel types of multilayer color-tunable organic light-emitting devices (OLEDs) with the structure of indium tin oxide (ITO)/N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB)/aluminum (III)bis(2-methyl-8-quinolinato)4-phenylphenolato (BAlq)/tris-(8-hydroxyquinolate)-aluminum (Alq₃)/Mg:Ag were fabricated. By inserting a thin layer with different thickness of a second NPB layer at the heterojunction interface of BAlq/Alq₃, the emission zone of devices shifted greatly and optoelectronic characteristics underwent large variation. Although BAlq was reported as a very good hole-blocking and blue-light-emission material, results of measurements in this paper suggested that a certain thickness of NPB layer between BAlq and Alq₃ plays an important role to modify device characteristics, which can act as recombination-controlling layer in the multilayer devices. It also provides a simple way to fabricate color-tunable OLEDs by just changing the thickness of this “recombination-controlling” layer rather than doping by co-evaporation.     

DPVBi空穴阻挡层对OLED性能的优化

研究了宽带隙有机小分子材料DPVBi作为空穴阻挡层对OLED器件效率和亮度的优化作用.DPVBi的引入有效地改善了以PEDOT:PSS做空穴注入层的OLED器件的空穴过剩问题.实验结果表明:通过优化DPVBi的厚度,插入30 nm厚的DPVBi空穴阻拦层可以有效地平衡OLED器件的电子和空穴浓度,降低器件的工作电压,优...     

DPVBi的厚度和发光位置不同对有机电致发光器件性能的影响

通过调整发光层DPVBi的厚度和在器件中的位置,在同一实验条件下设计了不同的器件结构,制备了有机电致发光器件,在实验中可看到DPVBi的厚度不同,器件的色度发生了改变,并且发现DPVBi在器件的不同位置,器件的发光特性也是不同的。通过实验可以得知处于器件不同位置的DPVBi,其发光机理是不同的,这是由于DPVBi和Alq3的最高未占有轨道(HOMO)能级相差不多,而它们的最低占有轨道(LUMO)能级相差0.4eV,这样DPVBi的存在有利于电子的注入,同时由于rubrene和DPVBi的HOMO相差0.5eV,这样空穴和电子就在rubrene和DPVBi的界面处形成激子复合而发光。也就是说,在rubrene之后的DPVBi对空穴有了阻挡作用,使器件中的空穴和电子达到平衡。通过改变DPVBi的厚度,制备了白光器件,这组白光器件,在7～17V变化范围内器件的色坐标从(0.35,0.37)到(0.33,0.35)变化不大,接近白光等能点(0.33,0.33),是色度比较好的器件。     

Red organic light-emitting devices with dotted-line doped emitting layers

High efficiency red organic light-emitting devices (OLEDs) with several dotted-line doped layers (DLDLs) were fabricated by using an ultra-high vacuum organic molecular-beam deposition system. The red OLEDs consisted of indium-tin-oxide (ITO)/N, N′-diphenyl-N, N′-bis(1-naphthyl)-(1, 1′-biphenyl)-4, 4′-diamine (α-NPD): 40 nm/tris(8-hydroxyquinoline)aluminum (Alq₃)+4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetra-methyljuloldyl-9-enyl)-4H-pyran (DCJTB); 3%wt.: x nm/(Alq₃+DCJTB; 3%wt./ Alq₃)_n−1: (30−x) nm/ Alq₃: 30 nm/Mg:Ag with n of 2, 4, 6, or 8, and x=30/(2n−1). The luminance yield of the device with 8 DLDLs was 75% higher than that of the device with a common doped layer. This was attributed to more formation of the excitons formed in a wider region resulting from the existence of the DLDLs. The dominant mechanisms of the dopant emission for the devices with DLDLs were described on the basis of the sequential carrier trapping process.     

Evidence for the changes in hole injection mechanism with a CoPc hole injection layer

The hole injection in hole-only devices with the structures of Al/N,N′-bis(1-naphthyle)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB)/ITO and Al/NPB/cobalt phthalocyanine (CoPc)/ITO were analyzed. With the combined analysis of current density–voltage and impedance measurement, the charge injection mechanism based on the injection limited current model was investigated. The NPB single layer device shows Richardson–Schottky type thermionic emission in the entire applied bias range. On the other hand, the device with the CoPc hole injection layer shows thermionic emission until the applied bias reaches 3.7 V. Increasing the bias further, Fowler–Nordheim tunneling dominates the charge injection. The changes of hole injection mechanism were discussed by evaluating the energy level changes with internal field distributions.     

一种改善红光顶发射OLED色纯度及角度依赖特性的方法研究

在Si/SiO₂衬底上生长金属银作为阳极,4,4,4-tris(3-methylphenylpheny-lamino)-triphenylamine(m-MTDATA):MoOx/m-MTDATA/N,N-bis-(1-naphthyl)-N,N-diphenyl-1,1-biphenyl-4,4-diamine(NPB)作为空穴注入及传输层,发光层采用4,4-N,N-dicarbazole-biphenyl(CBP)掺杂磷光染料(1-(phenyl)isoquinoline)iridium(III) acetylanetonate(Ir(piq)₂(acac))的结构,4,7-di-phenyl-1,10-phenanthroline(BPhen)作为空穴阻挡层及电子传输层,阴极为LiF(1 nm)/Al(2 nm)/Ag(20 nm)复合阴极结构.通过在光取出的复合阴极上方生长一层CBP光学覆盖层,有效地改善了复合阴极膜系的透射率,从而改善了顶发射结构的光学耦合输出特性,在提高器件的正向发光效率的同时还使色坐标往深红光区移动.并且生长光学覆盖层结构的器件角度依赖特性明显得到改善,这对于制作高显示质量的显示器件具有重要意义.在原有结构的基础上增加20 nm的NPB掺杂磷光染料Ir(piq)₂(acac)作发光层,从而得到双发光层结构为NPB:Ir(piq)₂(acac)(1%,20 nm)/CBP:Ir(piq)₂(acac)(1%, 20 nm).由于NPB具有较高的空穴迁移率,避免了由于光学厚度的增加而引起器件工作电压的大幅升高,而双发光层的结构有利于增大激子复合区域,提高辐射复合几率,减少非辐射损耗,实现主客体之间高效的三线态能量传递,相对单发光层顶发射结构,双发光层结构不仅提高了器件的发光效率,而且改善了器件的色坐标.     

Study of different roles phosphorescent material played in different positions of organic light emitting diodes

Phosphorescent materials are crucial to improve the luminescence and efficiency of organic light emitting diodes (OLED), because its internal quantum efficiency can reach 100%. So the studying of optical and electrical properties of phosphorescent materials is propitious for the further development of phosphorescent OLED. Phosphorescent materials were generally doped into different host materials as emitting components, not only played an important role in emitting light but also had a profound influence on carrier transport properties. We studied the optical and electrical properties of the blue 4,4′-bis(2,2-diphenylvinyl)-1,1′-biphenyl (DPVBi)-based devices, adding a common yellow phosphorescent material bis[2-(4-tert-butylphenyl)benzothiazolato-N,C2′] iridium(acetylacetonate) [(t-bt)₂Ir(acac)] in different positions. The results showed (t-bt)₂Ir(acac) has remarkable hole-trapping ability. Especially the ultrathin structure device, compared to the device without (t-bt)₂Ir(acac), had increased the luminance by about 60%, and the efficiency by about 97%. Then introduced thin 4,4′-bis(carbazol-9-yl)biphenyl (CBP) host layer between DPVBi and (t-bt)₂Ir(acac), and got devices with stable white color.     

Spectral studies of thin films based on poly(N-vinylcarzole) and red dopant

Organic light-emitting diodes were fabricated with a structure of indium-tin-oxide (ITO)/poly(N-vinylcarzole)(PVK):4-(dicyanom-ethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB)/8-tris-hydroxyquinoline aluminum (Alq₃)/lithium fluoride (LiF)/Al. The energy transfer from PVK to Alq₃ then to DCJTB and the charge trapping processes were investigated by employing the photoluminescence (PL) and electroluminescence (EL) spectra. With increasing thickness of the Alq₃ layer, the PL and EL emission from PVK were decreased gradually, which indicated that the effective energy transfer occurred from PVK to Alq₃ and then from Alq₃ to DCJTB. At the same time, we found that the exciton recombination zone could be adjusted by controlling the Alq₃ layer thickness and the applied voltages. The effects of different DCJTB concentrations on the optical and electrical characteristics of the devices were investigated, and an obvious red-shift was observed with the DCJTB dopant concentrations increasing in the PL and EL spectra.