Balancing the white emission of OLED by a design of fluorescent blue and phosphorescent green/red emitting layer structures

In this paper, we performed the design on the relative thickness of fluorescent–phosphorescent light emitters and evaluated the corresponding change of spectral characteristics of white organic light emitting diode (WOLED). Use of a 3-nm-thick separator composed of undoped phosphorescent host, which provides the confinement of singlet exciton, yields relatively well-defined broadband white emission. The optimized multilayers in WOLED comprises one of the simplest device structures among the reported fluorescent–phosphorescent hybrid WOLEDs, representing the Commission Internationale de l’Eclairage (CIE) 1931 chromaticity ranging from the nearly pure (0.30, 0.35) to warm white (0.35, 0.40) of 9.0–12.5 cd/A (24,000 cd/m² at 12 V bias). Although the presented efficiency data is not as high as the reports of others, design principles for a bright and stabilized three-peak-balanced white emission are discussed in detail, which will be beneficial for a step forwards in the development of broadband WOLED.     

A blue organic emitting diode derived from new styrylamine type dopant materials

We have designed and synthesized new dopant materials based on the styrylamine moiety, 4-[(1,2-diphenyl)-4′-(N,N-diphenyl-4-vinylbenzenamine)]biphenyl (4) and 4-[(1,2-diphenyl)-4′-(N,N-diphenyl-4-vinylbenzenamine)]terphenyl (8). Blue OLEDs were obtained from new styrylamine dopant materials and compared with those of blue dopant bis[4-(di-p-N,N-diphenylamino)styryl]stilbene (DSA-Ph) and diphenyl[4-(2-terphenyl vinyl)phenyl]amine (R-BD). The ITO/DNTPD/NPB/MADN:dopant/Alq₃/Al-LiF device obtained from 4 shows blue EL spectrum at 469 nm and high efficiency 3.02 cd/A at 7 V. 8 also shows blue EL spectrum around λ_max = 468 nm, efficiency of 3.51 cd/A and a current density of 25.94 mA/cm² (855.7 cd/m²) at 7 V.     

New amorphous electron-transporting materials based on Tris-benzimidazoles for all wet-process OLED devices

New amorphous electron-transporting materials 1,3,5-tris[1-(phenoxy phenyl)-1H-benzimidazol-2-yl]benzene (6a and 6b) were synthesized by dehydration reaction of corresponding triamides and fully characterized. Compounds 6a and 6b showed high thermal stability (T_g = 108 to 110 °C) and good solubility in common organic solvents, such as acetone, 2-methoxyetanol, tetrahydrofuran, chloroform, and 2-butanone. Pinhole-free transparent films were obtained by spin-casting the 2-butanone solution. 6a and 6b were fabricated as electron-transporting layer by spin-casting on a hole-transporting layer that was deposited by spin-cast beforehand and was insoluble in 2-butanone. Both devices showed no emission, but carrier transporting property was observed (400 mA/cm²). The device showed a blue emission (35 cd/m²) from 9,10-diphenylanthracene (DPA) when 10 wt.% DPA was mixed into the 6b layer.     

Thermally stable fluorescent blue organic light-emitting diodes using spirobifluorene based anthracene host materials with different substitution position

Thermally stable blue organic light-emitting diodes (OLEDs) were developed using anthracene based host materials with a spirobifluorene group. 4-Bromospirobifluorene and 2-bromospirobifluorene were attached to the anthracene core and the effect of the substitution position on the physical properties and device performances of the blue fluorescent OLEDs was investigated. The 4-spirobifluorene substitution was better than the 2-spirobifluorene substitution in terms of thermal stability and widened the bandgap of the anthracene based host material due to the geometrical structure of the material. However, the wide bandgap of the host material with 4-spirobifluorene had negative effect on the current density and efficiency of the blue devices.     

Highly efficient blue electroluminescence based on a new anthracene derivative

A novel blue-light-emitting material, 2,3,6,7-tetramethyl-9,10-dinaphthyl-anthracene (TMADN), was synthesized and characterized. Organic light-emitting diode (OLED), which has a double-layer structure, has been fabricated. In this OLED, the homemade TMADN was used as the light-emitting material and 4,7-diphenyl-1,10-phenanthroline (DPA) was used as the hole blocking/electron transporting material, N,N′-biphenyl-N,N′-bis-(1-naphenyl)-[1,1′-biphenyl]-4,4′-diamine (NPB) was used as the hole transporting material. The peak emission of electroluminescence (EL) is at about 456 nm and the CIE coordinates are (0.171, 0.228). The brightness of the device is up to 5600 cd/m² at 17 V with the maximum EL efficiency of 2.2 cd/A.     

White organic light-emitting devices with a bipolar transport layer between blue fluorescent and yellow phosphor-sensitized-fluorescent emitting layers

We report white organic light-emitting devices (WOLEDs) based on 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi) and phosphorescence sensitized 5,6,11,12-tetraphenylnaphthacene (rubrene). By introducing a bipolar transport 4,4′-N,N′-dicarbazole-biphenyl (CBP) layer between the fluorescent and the phosphor-sensitized-fluorescent layers, additional light emission from the phosphorescence sensitized layer is observed. This can be attributed to the elimination of the Dexter energy transfer between these two emitters. White emission with Commission International de L’Eclairage coordinates of (0.22,0.33) and a maximum luminance of 22,360 cd/m² were obtained. The maximum current efficiency can reach 10.7 cd/A.     

Broadly tunable deep blue laser based on a star-shaped oligofluorene truxene

We report amplified spontaneous emission (ASE) and optically pumped deep-blue-emitting distributed feedback (DFB) lasers based on a star-shaped oligofluorene truxene molecule. A low ASE threshold of 2.1 kW/cm² at 439 nm was achieved. The material exhibits a high net gain of 38 cm^?1 and also low optical loss coefficient of 3.5 cm^?1. Second-order DFB lasers show tuning of the emission wavelength from 422 to 473 nm, and a minimum threshold density of 515 W/cm². This is the broadest tuning range (51 nm) reported for organic deep-blue/blue lasing materials.     

Conversion of a green light emitting zinc-quinolate complex thin film to a stable and highly packed blue emitter film

Tris-(8-hydroxyquinoline) metal complex Znq₂, used as light-emitting layer in electroluminescent (EL) devices was synthesized and optical properties of as-deposited Znq₂ in thin films were studied. Interesting phenomenon was observed while studying the ageing and degradation behavior of Znq₂ films and consequently a stable form having strong blue photoluminescence (peak 465 nm) was discovered. This converted (from green to blue emitting) film has higher molecular packing density and comparable photoluminescence intensity with Znq₂ film. Here, we report on the production of this blue material under controlled conditions and its optical properties.The thin films have been deposited by thermal evaporation on quartz and silicon substrates. The optical constants (n and k) of green Znq₂ film and converted (to blue) thin films have been determined using spectroscopic ellipsometry. Environment induced effects on optical properties of films have been studied using ellipsometry, photoluminescence and UV–vis transmission measurements.     

氮化镓基高亮度发光二极管材料外延和干法刻蚀技术

通过对氮化镓(Gallium nitride,GaN)基蓝色高亮度发光二极管(High brightness light emitting diode,HB-LED)材料金属有机气相外延(Metal organic vapor phase epitaxy,MOVPE)生长技术的研究和优化以及在有源区内引入新型InxGa1-xN/GaN多量子阱(Multiple quantum wells,MQWs)结构,获得了高性能的HB-LED外延片材料.高分辨率X射线衍射(High resolution X-ray diffraction,HR-XRD)和变温光致荧光谱(Temperature dependent photoluminescence spectra,TD-PL Spectra)测量表明外延材料的异质界面陡峭,单晶质量优异,并由变注入电致荧光谱(Injection dependent electroluminescence spectra,ID-EL spectra)测量获得:HB-LED芯片的峰值发光波长在注入电流为2 mA至120 mA变化下蓝移量小于1 nm,电致荧光谱的半高全宽值(Full width hlf maximum,FWHM)在注入电流为20 mA时仅为18 nm.此外,还介绍了GaN基材料感应耦合等离子体(Inductivelycoupled plasma,ICP)干法刻蚀技术.考虑实际需要,本文作者开发了AlGaN/GaN异质材料的非选择性刻蚀工艺,原子力显微镜(Atomic force microscope,AFM)观察得到AlGaN/GaN刻蚀表面均方根粗糙度RMS仅为0.85nm,与外延片的表面平整度相当.还获得了AlGaN/GaN高选择比的刻蚀技术,GaN和AlGaN的刻蚀选择比为60.     

Novel efficient blue materials with 4H-cyclopenta[def]phenanthrene for OLEDs

Novel blue emitters, 2-[10-(4,4-dioctyl-4H-cyclopenta[def]phenanthrene-2-yl)-9-anthryl]-4,4-dioctyl-4H-cyclopenta[def]phenanthrene (OCPA) and 4,4,4′,4′,4″,4″-hexaoctyl-2,6′:2′,6″-tercyclopenta[def]phenanthrene (TerCPP) have been synthesized and characterized. The introduction of cyclopenta[def]phenanthrene units into the structure of OCPA and TerCPP leads LEDs with high efficiency and pure blue emission. Thermal analysis of OCPA and TerCPP reveals their high thermal stability. Their decomposition temperatures are around 410 °C for OCPA and 425 °C for TerCPP. The high-quality amorphous films of OCPA and TerCPP were prepared by vapor deposition. UV–visible absorption spectra of the thin films of these compounds appear at about 303–400 nm, and their maximum PL emission appeared at about 434 and 401 nm, respectively. The multi-layered OLEDs with the configuration of ITO/with or without PEDOT:PSS/NPD/OCPA or TerCPP/BAlq or BCP/Alq₃/LiF/Al were fabricated to investigate the electroluminescent properties and the current–voltage–luminescence characteristics of the compounds. Multi-layer organic EL devices with OCPA and TerCPP as an emitting layer produced bright blue (434 nm) and sky blue emissions (440 nm), respectively. The device of OCPA with the configuration of ITO/NPD/OCPA/BAlq/Alq₃/LiF/Al showed the turn-on voltage of about 5.6 V, the maximum brightness of 2500 cd/m² (at 11 V), the maximum luminescence efficiency of 1.2 cd/A, and CIE coordinates of 0.16 and 0.12 which are quite close to that of the National Television System Committee (NTSC) standard blue (0.14, 0.08).     

Synthesis and characterization of efficient luminescent materials based on 2,1,3-benzothiadiazole with carbazole moieties

Two new luminescent materials named 4-bromo-7-carbazyl-[2,1,3]-benzothiadiazole (3) and 4,7-dicarbazyl-[2,1,3]-benzothiadiazole (4) were obtained by a modified Ullmann reaction in one step from 4,7-dibromo-[2,1,3]-benzothiadiazole (2) (based on 2,1,3-benzothiadiazole (1, BTD)) and carbazole. The structure and purity of them were characterized by crystal structures, ¹H NMR and elemental analysis. Compared with compounds 1 and 2, the compounds 3 and 4 have better optical properties and thermostability due to the introduction of the carbazole moieties, and the compound 4 shows better performances than that of compound 3. For compound 4, a strong absorption peak at 236 nm with a high extinction coefficient up to 1.205 × 10⁵ L·mol·cm^?1 and bright green to orange photoluminescence with quantum yields of 9.0%, 48.4%, 51.0% and 75.6% in different solvents of acetonitrile, dichloromethane, ethyl acetate, and diethyl ether, respectively, were measured.     

叶片气膜孔的电火花加工工艺研究

叙述了高速电火花小孔加工的工作原理和加工工艺。通过实际工件的加工试验，得出叶片型面上小孔的最佳加工工艺参数，采用此工艺方法加工后的小孔，其表面质量、尺寸精度、形状精度均符合设计要求，为叶片型面上的小孔加工提供了一种可靠、实用的方法。     

谐振型电火花加工脉冲电源的研究

分析了限制电火花加工脉冲电源高频化的因素，利用并联谐振软开关技术和高速功率MOSFET器件，设计了一种新型电火花加工脉冲电源，对这种新型电源的工作原理进行了探讨与分析。     

A highly efficient hybrid inductive joining technology for metals and composites

A hybrid technology of inductive contact joining (ICJ) was developed to join fibre-reinforced thermoplastics (FRP) with metals by using a tool with single-sided heating. In comparison to conventional methods with separate heating, pressing and cooling, the unique new hybrid ICJ process is characterized by combining all three steps into one hybrid process. The maximum temperature is shifted toward the joining zone due to the direct cooling effect of the surface. FE simulations showed the temperature distributions within the joint. The performed experiments provided data for the temperature profile of the process and the resulting strength of the joint, type of damage and microstructural characteristics. Proven advantages include very short cycle time, competitive joint strength and limited influence on the mechanical properties of the metallic component.     

Organic light-emitting devices (OLED) based on new triphenylamine derivatives

In this paper, we reported the synthesis of two new triphenylamine derivatives: 1,4-bis[-E-4-(N,N-diphenylamino)styryl]naphthalene (Np-G1) and 2,8-bis[-E-4-(N,N-diphenylamino) styryl]dibenzothiophene (ST-G1) and investigated the electroluminescence characteristics of the three-layer devices with Np-G1 or ST-G1 as emitting layer. The results have shown that introduction electron-acceptor group, naphthalene, into triphenylamine units, Np-G1 with linear geometric conformation can lower its LUMO level obviously and resulting facilitate electron injection and transport for the device. Thus, the three-layer device (ITO/TCTA/Np-G1/BCP /Mg:Ag) improved the electroluminescence properties the best, presenting the brightness of ～10,000 cd/m² and current efficiency of ～3.0 cd/A. On the other hand, ST-G1 with V-shaped conformation containing dibenzothiophene linked triphenylamine groups cannot effectively decreased its LUMO level. As a result, ST-G1 has little contribution to the carrier recombination within itself.     

3,6-Di(9-carbazolyl)-9-(2-ethylhexyl)carbazole based single-layer blue organic light emitting diodes

The electroluminescent device ITO/CuI/3,6-di(9-carbazolyl)-9-(2-ethylhexyl)carbazole(TCz1)/Ca/Al in which TCz1 for the first time was used as the emitting layer, was fabricated by means of vacuum deposition. The device emits blue light with a peaks at 388 and 406 nm at 4.5 V, with high current efficiency values (11.5 cd/A) and external quantum efficiency (1.72%).     

A study on the analytical modeling for warm hydro-mechanical deep drawing of lightweight materials

The warm hydroforming process has become an emerging technology in recent years to reduce the weight of automotive body structure and minimize the number of process steps. In this study, analytical models were developed to investigate the effects of process conditions such as temperature, hydraulic pressure, blank holder force and forming speed. The analytical model under hydro-mechanical deep drawing (HMD) condition was developed based on experimental results in the literatures. FE models were also developed to validate the analytic models. Then, the analytic model was validated through comparisons with both existing experimental results and FE results. The analytical model provided rapid and reasonably accurate results for the design of warm hydroforming process. Based on this analytic model, several parametric studies were performed regarding to the temperature, hydraulic pressure, blank holder force, and punch speed conditions. It was demonstrated that the process windows for a successful part forming could be rapidly predicted with a reasonable accuracy by the analytic model compared to lengthy and costly thermo-mechanical FEA or experimental trial and error.     

基于Hosford屈服函数的横观各向同性金属材料拉深成形塑性及变形分析

为了研究板材拉深中的成形极限,对金属材料的拉深成形进行塑性及变形分析。以横观各向同性材料为研究对象,采用对实验数据拟合能力较好的Hosford屈服函数,对拉深成形过程中法兰区的变形性能进行分析,得到法兰区应力场;采用数值积分拟合的方法,给出拉深冲杯杯高数值积分拟合表达式,并用η=2时的杯高解析表达式对此拟合方法的可靠性进行验证;利用Zwick万能试验机和拉深试验机,对铝板进行了拉伸和冲杯实验,验证了杯高表达式的正确性;利用杯高数值积分拟合表达式计算杯高,η=8的结果相对η=2的结果更接近实测杯高,说明了Hosford屈服函数比Hill48屈服函数对金属材料的塑性变形拟合效果更好。     

一种基于CNN深度学习的焊接机器人视觉模型

为了准确地识别复杂环境下的焊缝目标,建立了一种基于深度学习的焊接机器人视觉模型,该模型采用局部联接和全联接相结合的CNN卷积神经网络结构,局部联接由3个卷积层和子采样层交替组成,用于焊接目标的特征提取,全连接层由输入层、隐层和输出层组成,作为分类器用于焊缝目标识别. 采样了一千多幅焊接目标图像样本用于CNN的网络训练,分析了不同CNN网络结构参数对模型的影响. 结果表明,该视觉模型对焊接目标的平移、旋转和比例缩放表现出良好的鲁棒性,可以应用到焊接机器人的视觉导航.     

Deep blue organic light-emitting diodes based on triphenylenes

We report about new easy-to-synthesize deep blue light-emitting organic materials. Various substituted low-molecular-weight triphenylene-derivatives have been prepared in a one-step procedure and are easily available on large scale and high purity. Furthermore, the synthesis of an oxetane functionalized, photo-crosslinkable triphenylene-based emitter material with enhanced film-forming properties is described. The low-molecular-weight emitters were vacuum-deposited, whereas the photo-crosslinkable emitter material derivative was processed from solution. The optical and electrical properties of the compounds were investigated. The corresponding photoluminescence emission spectra exhibit λ_max,ems values around 400 nm. Organic light-emitting multi layer devices were fabricated and characterized. OLED devices from these molecules emit deep blue light of 436–456 nm.