Electroluminescent devices based on polymers forming hole-transporting layers. II. Polyimides containing β-naphthyldiphenylamine units

Two polyimides, PI(C1-BA) and PI(C1-6FDA), based on an aromatic diamine compound and two aromatic dianhydrides [biphenyltetracarboxylic dianhydride (BA) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA)] were newly synthesized. They were characterized by viscosity, Fourier transform infrared measurements, and X-ray analyses. X-ray results revealed that the crystallinity of PI(C1-BA) was lower than that of PI(C1-6FDA). The synthesized polyimides could be formed into stable and homogeneous thin films on an ITO (indium tin oxide) electrode, functioning as good hole-transport materials for organic electroluminescent (EL) devices. The double-layered EL devices, consisting of the hole-transport layer of these polyimides and an emitting layer of tris(8-quinolinolato)aluminum complex, exhibited a peak emission wavelength in the bright green at 524–527 nm. Moreover, a maximum luminance of 355 cd/m² was achieved at a voltage of 13 V, with a current density of 600 mA/cm² for the EL device using PI(C1-BA) as a hole-transport layer. The phenomenon of an extended luminance of these EL devices was also found when the voltage was applied higher than 13 V. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2032–2040, 2000     

含有载流子传输功能基团咔唑和噁二唑的有机铕(Ⅲ)配合物的合成及其发光性能

合成了一种含有载流子传输功能基团咔唑和噁二唑的有机铕(Ⅲ)配合物. 在研究了光致发光等性能的同时, 制备了结构为ITO/NPB(40 nm)/2.5%铕(Ⅲ)配合物: CBP(30 nm)/BCP(10 nm)/Alq3(30 nm)/LiF(1 nm)/Al(100 nm)的电致发光器件, 器件在612 nm处有半峰宽为4 nm的高纯度的明亮红光发射, 起亮电压约为6 V, 在17.3 V时达到最大亮度1778 cd/m2.     

以N,N-四(间联苯基)-4,4-联苯二胺为正孔传送材料的有机电致发光器件(英文)

用新的路径成功地合成了N,N -四(间联苯基)-4,4 -联苯二胺(m TBPBz).以m TBPBz作为正孔传送材料,探讨了它在有机电致发光器件中的应用.制作了结构为玻璃基板／ITO阳极(130nm)／m TBPBz(40nm)／Alq(60nm)／LiF(0.5nm)／Al阴极(100nm)的器件.结果显示:该有机电致发光器件的绿色发光来源于Alq层.10V时,它的最大亮度为9486cd／m2.证明了m TBPBz具有正孔传送性能,可作为电致发光材料使用.     

基于蓝黄磷光二元互补色的高效聚合物白光器件

研究了基于互补色的高效聚合物白光器件,双色材料包括蓝绿光材料双(4,6-二氟苯基吡啶-N,C2)吡啶甲酰合铱(Firpic)和黄光材料三[3-(2,6-二甲基苯氧基)-6-(2-噻吩基)-哒嗪]铱(Fs-1),器件结构为ITO/PEDOT(40 nm)/PVK:OXD-7:Firpic:Fs-1(80 nm)/Ba(4 nm)/Al(120 nm).当发光层材料PVK∶OXD-7∶Firpic∶Fs-1质量比为63∶27∶10∶0.25时,用溶液加工方法得到高效白光器件,此时CIE色坐标为(0.30,0.39),最大电流效率为10.8 cd.A-1,亮度可达到4200 cd.m-2.在此基础上,引入水溶性电子注入材料聚[9,9-二(3′-N,N-二甲基胺基丙基-2,7-芴-2,7-交-(9,9-二辛基芴)](PFN)修饰阴极界面,使载流子注入和传输更平衡,当阴极为PFN(20 nm)/Al(120 nm)时,电流效率获得显著改善,达到13.1 cd.A-1,此时电流密度为4.9 mA.cm-2,亮度可达到6096 cd.m-2,白光器件的色坐标为(0.33,0.39),同时发光光谱稳定.另外通过电致发光(EL)、光致发光(PL)光谱及能级结构图分析了载流子俘获和能量转移在发光中的作用.     

On the Complementary Photoluminescent and Electroluminescent Images of Poly(phenylenevinylene)‐Based Light‐Emitting Diodes with a Thin Active Layer

A clear complementary relationship between photoluminescent (PL) and electroluminescent (EL) images was observed for organic light‐emitting diodes (OLEDs) based on poly(phenylenevinylene) (PPV) and dye‐doped PPV. So‐called ‘black spots' (dark circular regions observed on the active area of running OLEDs) become bright ones, when the photoluminescence of the same area is excited. A very small thickness of the active layer (ca. 10 nm) was the crucial point to observe this anticorrelation between EL and PL. A substantial increase of the PL yield (‘anti‐burning' effect) was observed after strong light exposure (ca. 10 mJ/cm²) of the polymer covered by an aluminium layer. The same light exposure without aluminium protection resulted in complete photobleaching of the polymer. The presence of a thin insulating layer between the polymer and aluminium was proposed to be responsible for these effects. This layer prevents electron injection and PL quenching due to exciton dissociation at the metal‐polymer interface. The former effect leads to black spots in the EL image, the latter one gives rise to bright spots on the PL image situated on the same places. The intermediate layer can be also induced by light exposure. A very efficient energy transfer from the polymer to the dye and to the J‐aggregates of the dye was demonstrated in PPV/dye composite films.     

A CuO Nanowire‐Based Alternating Current Oxide Powder Electroluminescent Device with High Stability

An AC‐driven powder electroluminescent (EL) device has been achieved by constructing a CuO nanowire–Zn₂GeO₄:Mn phosphor heterogeneous junction. The CuO nanowires enhance the local electric field, resulting in electroluminescence of an oxide‐based phosphor in EL devices owing to field injection at the nanowire tips. The CuO nanowire array was synthesized by an in situ thermal oxidation method at 400 °C in air and employed as an electric field enhancement layer in the EL device. The heterogeneous structures were created through drop coating of a phosphor suspension on the CuO nanowire array. The initial EL device tests show good luminescent performance with very promising brightness maintenance for over 360 h, with a loss of luminescent intensity of under 1 % at over 10 cd m^?2 luminance. The fabrication method offers the prospect of simple, low‐cost, large‐scale EL devices with the potential to solve the limited operational lifetime of sulfide‐based AC powder EL devices.     

Monochromatic‐red‐light emission of novel copolymers containing carbazole units and europium–acrylate complexes

Nearly monochromatic‐red‐light‐emitting polymers with pendant carbazole and europium (Eu) complex were synthesized and characterized by Fourier transform infrared, elemental analysis (EA), ¹H NMR, ¹³C NMR, UV, and gel permeation chromatography. The photoluminescence and electroluminescence (EL) properties of these polymers were investigated. A single‐layer light‐emitting‐diode device of the structure (indium tin oxide/polymer P4/Al) was fabricated, showing the characteristic bright‐red EL of the Eu³⁺ complex at 614 nm at a turn‐on voltage of about 17 V. The EL spectrum, current–voltage, and emission‐intensity–voltage characteristics of the device were measured. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3405–3411, 2000     

Organic electroluminescent device based on electropolymerized polybithiophene as the hole-transport layer

An ultrathin film of polybithiophene (PBTh), used in organic electroluminescent (EL) devices, was generated by an electrochemical method with a conducting indium tin oxide (ITO) glass as the working electrode. The light-emitting layer could be deposited directly onto the PBTh by using spin coating for fabrication of the organic EL devices. It was found that the film of PBTh as the hole-transport layer for the EL device could effectively raise the EL intensity and efficiency. The EL intensity of the ITO/PBTh/emitting layer/Al device is about 100 times as strong as that of the ITO/emitting layer/Al device at the same current density of 50 mA/cm².     

Luminescence properties of poly(p‐phenylenevinylene) derivatives carrying directly attached hole‐transporting carbazole and electron‐transporting phenyloxadiazole pendants

New poly(p‐phenylenevinylene) (PPV) derivatives ( polymer 1 and 2 ) that carry hole‐transporting carbazole and electron‐transporting phenyloxadiazole pendants were synthesized and their photo‐ and electroluminescence properties were studied. Polymer 1 is poly[2‐(N‐carbazolyl)‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] that has both carbazole and 2‐ethylhexyl pendant groups. And polymer 2 is poly[2‐{4‐[5‐(4‐t‐butylphenyl)‐1,3,4‐oxadiazolyl]phenyl}‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene], which bears the 2‐(4‐t‐butylphenyl)‐5‐phenyl‐1,3,4‐oxadiazole pendants. The optical properties of the polymer films were studied by UV‐vis absorption, photoluminescence (PL) and electroluminescence (EL) spectroscopy. EL devices with the configuration of ITO/poly(3,4‐ethylenedioxy‐2,5‐thienylene) (PEDOT) polymer/Ca/Al were constructed and the device performances were compared. Polymer 1 emits bright yellowish green light (λ_max = 530 nm), whereas polymer 2 emits yellowish orange (λ_max = 540 nm) light. The device fabricated using polymer 1 showed a low turn‐on electric field of 0.31 MV/cm and the maximum luminance of 30,390 cd/m² at 1.50 MV/cm. Polymer 2 exhibited a little poorer device performance (turn‐on electric field: 0.94 MV/cm; maximum luminance: 5,720 cd/m² at 2.74 MV/cm). Maximum photometric efficiencies of the devices were 4.4 and 1.3 cd/A, respectively.     

Bright White Organic Light-Emitting Diode Mixed Blue and Green Emission

Double-layer and triple-layer organic light-emitting diodes (OLEDs) were fabricated using a novel star-shaped hexafluorenylbenzene organic material, 1,2,3,4,5,6-hexakis(9,9-diethyl-9H-fluoren-2-yl)benzene (HKEthFLYPh) as an energy transfer layer, N, N′-bis-(1-naphthyl)-N, N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) as a hole-transport layer (HTL) and blue emissive layer (EML), and tris(8-hydroxyquinoline)aluminum (Alq₃) as an electron-transport layer (ETL) and green light-emitting layer. Bright white light was obtained with a triple-layer device structure of indium-tin-oxide (ITO)/NPB (40 nm)/HKEthFLYPh (10 nm)/Alq₃ (50 nm)/Mg:Ag (200 nm). A maximum luminance of 8523 cd·m⁻² at 15 V and a power efficiency of 1.0 lm·W⁻¹ at 5.5 V were achieved. The Commissions Internationale de L′Eclairage (CIE) coordinates of the device were (0.29, 0.34) at 9 V, which located in white light region. With increasing film thickness of HKEthFLYPh, light emission intensity from NPB increased compared to that of Alq₃.     

含腈基的三苯胺基二苯乙烯化合物的合成及其电致发光性能研究

本文成功地合成了集空穴传输基团三苯胺和电子受体基团腈基于一个分子中的腈基取代的三苯胺基二苯乙烯系列化合物,获得电子和空穴都能够高效注入和传输的新型电致发光材料.由这种材料制备的电致发光器件的性能稳定,启动电压显著降低,发光为黄绿色.     

A novel oligothiophene derivative as a hole‐transport with emitting material for OLED

A novel oligothiophene derivative containing the triphenylamine moiety with high glass transition temperature (T_g; 135 °C), 5,5′‐{bis[4‐di(4‐thiophenyl)amino]phenyl}‐2,2′‐bithiophene (TTPA‐dimer) was synthesized by the dimerization of tris[4‐(2‐thienyl)phenyl]amine (TTPA) with a palladium catalysis. Some types of electroluminescent (EL) devices that use the amorphous material for a hole‐ and an electron‐transporting with an emitting layer were fabricated. These devices emitted a bright green‐yellowish light (λ_emi; around 510 nm) with a small full width at half maximum (FWHM) rather than that of Alq₃. The single layer EL device showed a maximum luminance of 221 cd/m² at 8 V (0.06 lm/W at 100 cd/m²). On the other hand, the double layer (TTPA‐dimer/Alq₃) EL device that used Alq₃ as the electron transport material was increased up to 10830 cd/m² at 12 V (0.89 lm/W at 300 cd/m²) and with a lower turn‐on voltage (3.2 V at 0.1 cd/m²) than other types of EL devices. Copyright © 2003 John Wiley & Sons, Ltd.     

Charge transport polymers for organic electroluminescent devices

Triple-layer-type organic electroluminescent devices were fabricated using charge-transporting poly(N-vinylcarbazole) (PVK) as a hole-transporting emitter layer. Electron-transporting layers consisting of a triazole derivative (TAZ) and an aluminum complex (Alq) layer were used to maximize the carrier recombination efficiency. The EL device with a structure of glass substrate/indium-tinoxide/PVK/TAZ/AIq/Mg:Ag showed bright blue emission from the PVK layer with a luminance of over 700 cd/m². The emission color was tuned to a desirable color in the visible region through doping the PVK layer with fluorescent dyes. Bright white emission, in particular, was obtained for the first time at a high luminance level of over 3000 cd/m² by using three kinds of fluorescent dyes each emitting red, green or blue.     

多芳胺取代均三嗪的合成及其光电性能的研究

设计合成了一个新的带有三支链的均三嗪衍生物分子: 2,4,6-三[4-(N,N-二对甲苯基)-苯胺乙基]均三嗪(TBTN); 用1H NMR, 13C NMR, IR, MS (MALDI-TOF)和元素分析确认了化合物的结构. 研究了该化合物的紫外吸收光谱、荧光光谱、电致发光光谱等性能, 用TBTN组装发光器件, 实验结果显示TBTN为发光层时, 该器件能发出稳定白光. 器件结构为ITO/2-TNATA (30 nm)/NPB (20 nm)/TBTN (30 nm)/Alq3 (30 nm)/LiF (0.5 nm)/Al, 在电压为15 V获得最大亮度是1523 cd/m2, 在驱动电压范围内CIE(国际照明委员会)坐标稳定并在白色等能区内.     

High luminance phosphorescent organic light emitting diodes based on Re(I) complex

A novel Re(I) complex with the acenaphtho[1,2-b]pyrazino[2,3-f][1,10]phenanthroline (APPT) ligand Re(APPT)(CO)₃Br (abbreviated as Re-APPT) was used to fabricate organic light emitting diodes (OLEDs). From the electroluminescence (EL) spectra of the device at different bias voltages, it could be found that the EL maxima shifted approximately 30 nm. For OLEDs with 5% Re-APPT doped emissive layer, turn-on voltage of 6 V, maximum luminance of 7631 cd/m² and a current efficiency up to 2.36 cd/A were obtained. We suppose that a direct charge trapping took the dominant position in the EL process. Trapping contributed mostly to this relatively higher luminance.     

Synthesis,characterization, and electroluminescent performance of a novel copolyfluorene containing pendant crown ether groups

Copolyfluorene PFC containing pendant crown ether moieties was prepared by the palladium‐catalyzed Suzuki coupling reaction. The photo‐physical and electrochemical properties were investigated by absorption, photoluminescence (PL) spectroscopy, and cyclic voltammetry to elucidate the influence of the crown ether groups. In film state, its PL spectra (peaked at 430 and 452 nm) show noticeable red‐shift relative to 423 and 448 nm of poly(9,9‐dihexylfluorene) ( PF ). Thermal annealing leads to appearance of new emission at about 520 nm which has been attributed to formation of excimer. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels of PFC were estimated to be ?5.68 and ?2.65 eV which contributed to balanced charges injection. Double‐layer electroluminescent device using PFC as emitting layer (ITO/PEDOT:PSS/ PFC /Ca/Al) revealed maximum luminance (7910 cd/m²) and maximum luminance efficiency (2.3 cd/A) superior to those of PF device (860 cd/m², 0.29 cd/A). Moreover, inserting a PFC layer between the PF emitting layer and calcium cathode led to reduced turn‐on voltage (4.1 V), much lower than 7.1 and 6.6 V of the double‐layer PFC and PF devices, respectively, and enhanced device performance (2800 cd/m² and 0.53 cd/A). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2985–2995, 2009     

Synthesis, characterization and photophysics of fluorene-alt-oxadiazole copolymers containing pendent iridium (III) complex moiety

A series of fluorene-alt-oxadiazole copolymers containing a pendent phosphor chromophore of the (piq)₂Ir(pic) complex were synthesized via the palladium-catalyzed Suzuki coupling reaction, where piq is 1-phenylisoquinoline and pic is picolinic acid. These copolymers exhibited a similar absorption spectrum with a peak at about 330 nm and a typical emission peak at 408 nm in CH₂Cl₂ from the fluorene-alt-oxadiazole backbone. However, a significantly red-shifted emission peak at about 625 nm was observed in the neat films of these copolymers, which are attributed to the pendent iridium (III) complex unit. Using these copolymers as single emission layer, the polymer light-emitting devices with a configuration of ITO/PEDOT:PSS/copolymers/LiF/Al exhibited a saturated red emission with a peak at 632 nm. Significant influence of the attached iridium (III) complex ratio on EL performance was presented. A maximum current efficiency of 1.2 cd/A at 63 mA/cm² and a maximum luminance of 1125 cd/m² at 12 V were achieved from the device with the copolymer containing iridium (III) complex in a 3% molar ratio.     

混合蓝色和绿色发射的高亮度白色有机电致发光器件

使用星形六苯芴类新材料1,2,3,4,5,6-hexakis(9,9-diethyl-9H-fluoren-2-yl)benzene (HKEthFLYPh)分别制备了三种不同结构的有机电致发光器件. 在结构为indium-tin oxide (ITO)/NPB (40 nm)/HKEthFLYPh (10 nm)/Alq3(50 nm)/Mg:Ag (200 nm)的器件中, 获得了两个电致发光谱峰分别位于435 和530 nm处的明亮白光. HKEth-FLYPh是能量传输层; N,N’-bis-(1-naphthyl)-N,N’-diphenyl-(1,1’-biphenyl)-4,4’-diamine (NPB)是空穴传输层和蓝色发光层; tris(8-hydroxyquinoline)aluminum (Alq3)是电子传输层和绿色发光层. 结果表明, 当驱动电压为15 V时, 器件的最大亮度达到8523 cd·m-2; 在5.5 V时, 器件达到最大流明效率为1.0 lm·W-1. 在电压为9 V时, CIE色坐标为(0.29, 0.34). 此外, 通过改变HKEthFLYPh层的厚度, 发现蓝色发射的相对强度随着HKEthFLYPh层厚度的增加而增强.     

稀土配合物Eu(DBM)3为发光体的有机电致发光器件

分别以稀土配合物为发光中心，以PPV、Alq3为空穴输送层和电子输送层制备了结构为ITO／PPV／PVK：PBD：Eu（DBM）3／Alq3／Al的电致发光器件，其中发射层由旋涂法形成，该器件的最大亮度为52cd·m－2，且具有很好的单色性。     

Synthesis,characterization, and optoelectronic properties of hyperbranched polyfluorenes containing pendant benzylether dendrons

Linear polyfluorenes with low generation of side benzylether dendrons ( PLG0 , PLG1 ) and hyperbranched polyfluorenes with 1,3,5‐benzene branch unit ( PHG0 and PHG1 ) were prepared by the Suzuki coupling reaction to investigate the structural effect on optoelectronic properties. Their optical properties, both in solution and film state, were investigated using absorption and photoluminescence (PL) spectra. The excimer emission of polyfluorene at about 530 nm, induced by thermal annealing, was completely suppressed by the hyperbranched structure, but the suppression was not obvious by the side benzylether dendrons. The optoelectronic performance of the EL devices (ITO/PEDOT:PSS/polymer/Ca/Al) was strongly dependent upon chemical structures of the emitting polyfluorenes. The hyperbranched PHG0 with zero generation of benzylether side groups revealed the best device performance, with maximal luminance and maximal luminance efficiency of 2350 cd/m² and 0.33 cd/A, respectively. The results suggest that incorporation of branch units with low generation of benzylether dendrons is an effective way to improve annealing stability and EL performance of the polyfluorenes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5945–5958, 2008