Solution-processed WOx hole injection layer for efficient fluorescent blue organic light-emitting diode

Solution-processed tungsten oxide (s-WO_x) interfacial layer for efficient hole injection in fluorescent blue organic light-emitting diode (OLED) is demonstrated. The OLED using 2-methyl-9,10-bis(naphthalen-2-yl)anthracene (MADN) as emitter shows luminous efficiency of 3.3 cd/A, power efficiency of 2.5 lm/W and external quantum efficiency of 4.6% with Commission Internationale d'Eclairage (CIE) color coordinates of (0.154, 0.102). Using MADN doped 1-4-di-[4-(N,N-diphenyl)amino]styryl-benzene as emitter, luminous efficiency of 10.8 cd/A, power efficiency of 6.4 lm/W and external quantum efficiency of 7.2% with CIE color coordinates of (0.167, 0.283) are achieved. Atomic force microscopy and X-ray photoelectron spectroscopy show that s-WO_x features superior film morphology and non-stoichiometry with slight oxygen deficiency. Current-voltage characteristics and impedance spectroscopy analysis indicate that s-WO_x behaves slightly enhanced hole injection and accordingly contributes to improved device performance in comparison with conventional vacuum thermal evaporation WO_x. Our results pave an alternative way for broadening WO_x application with solution process and advancing fluorescent blue OLEDs.     

Performance improvement of GaN-based light-emitting diode with a p-InAlGaN hole injection layer

The characteristics of a blue light-emitting diode(LED)with a p-InAlGaN hole injection layer(HIL)is analyzed numerically.The simulation results indicate that the newly designed structure presents superior optical and electrical performance such as an increase in light output power,a reduction in current leakage and alleviation of efficiency droop.These improvements can be attributed to the p-InAlGaN serving as hole injection layers,which can alleviate the band bending induced by the polarization field,thereby improving both the hole injection efficiency and the electron blocking efficiency.     

Electroluminescence performance of organic light-emitting devices with KCl inside hole transport layer

A new multilayer organic light-emitting device (OLED) is fabricated by inserting kalium chloride (KCl) thin layer (1 nm) into hole transport layer (HTL). It has the configuration of ITO/NPB(15 nm)/KCl(1 nm)/NPB(25 nm)/Alq₃(60 nm)/KCl(1 nm)/Al. The electroluminescence (EL) result shows that the performance of the novel device has obviously improvement compared with the normal structure (ITO/NPB(40 nm)/Alq₃(60 nm)/KCl(1 nm)/Al). The EL and efficiency are about 1.4 and 1.3 times than that of conventional device. The suggested mechanism is that the KCl layer in N,N′-diphenyl-N,N′-bis(1-napthyl–phenyl)-1,1′-biphenyl-4,4′-diamine (NPB) can block the holes of NPB and then balance the holes and electrons. The better recombination of holes and electrons is beneficial to the enhancing properties of OLED.     

Enhanced luminance of white organic light-emitting diode with yellow nanophosphors-embedded blue polymer emitting layer

White organic light-emitting device was achieved through an incorporation of yellow YAG nanophosphors into blue polyfluorene emitting layer: electrode/YAG@polyfluorene/hole-transport/injection layers/ITO glass. The brightness of the proposed device (230 cd/m² at 30 V) was enhanced by a factor of about two in comparison with that of phosphor-free reference device. It is attributed to the increased local electric field caused by bumps of nanophophors on the emitting layer. With increase of voltage, the blue-green emission decreased whereas the yellow emission increased. It is due to the effective energy transfer from the blue-green to the yellow bands.     

The performance enhancement in organic light-emitting diode using a semicrystalline composite for hole injection

A semicrystalline composite, 3, 4, 9, 10 perylenetetracarboxylic dianhydride （PTCDA） doped N,N＇-di（1-naphthyl）- N,N＇-diphenylbenzidine （NPB）, has been fabricated and characterized. An organic light-emitting diode using such a composite in hole injection exhibits the improved performance as compared with the reference device using neat NPB in hole injection. For example, at a luminance of 2000 cd/m2, the former device gives a current efficiency of 2.0cd/A, higher than 1.6cd/A obtained from the latter device. Furthermore, the semicrystalline composite has been shown thermally to be more stable than the neat NPB thin film, which is useful for making organic light emitting diodes with a prolonged lifetime.     

具有新型双空穴注入层的有机发光二极管

采用新型双空穴注入层N, N, N', N'-tetrakis(4-Methoxy-phenyl)benzidine/Copper phthalocyanine(MeO-TPD/CuPc)及器件结构:ITO/MeO-TPD(15 nm)/CuPc(15 nm)/ N, N'-Bis(naphthalen-1-yl)-N, N'-bis(phenyl)benzidine (NPB, 15 nm)/8-hydroxyquinoline (Alq₃, 50 nm)/LiF(1 nm)/Al(120 nm), 研制出高效有机发光二极管(器件D), 与其他器件(器件A, 没有空穴注入层的器件; 器件B, MeO-TPD单空穴注入层; 器件C, CuPc单空穴注入层)相比, 其性能得到明显改善. 器件D的起亮电压降至3.2 V, 比器件A, B, C的起亮电压分别降低了2, 0.3, 0.1 V. 器件D在10 V时, 其最大亮度为23893 cd/m², 最大功率效率为1.91 lm/W, 与器件A, B, C的最大功率效率相比, 分别提高了43% (1.34 lm/W), 22% (1.57 lm/W), 7% (1.79 lm/W). 性能改善的主要原因是由于空穴注入和传输性能得到了改善, 通过单空穴型器件的J-V 曲线对这一现象进行了分析. 关键词： 有机发光二极管 空穴注入层 功率效率 势垒     

NPB:CBP复合空穴传输层对黄色有机电致发光器件的影响

采用N, N'-diphenyl-N, N'-bis(1-naphthyl-pheny1)-1, 1'-biphenyl-4, 4'-diamine (NPB):4, 4'-N, N'-dicarbazole-biphenyl (CBP) 掺杂体系为复合空穴传输层,制备了结构为indium-tin oxide (ITO)/NPB:CBP/CBP:bis iridium (acetylacetonate) /2, 9-dimethyl-4, 7-diphenyl-p 关键词： 有机电致发光器件(OLEDs) 复合空穴传输层 NPB:CBP 器件性能     

水溶性CuPc旋涂转速及退火方式对蓝色有机电致发光器件性能的影响

本文以Be(PP)₂为发光层、水溶性酞菁铜(WS-CuPc)为空穴注入层、NPB为空穴传输层,制备了结构为ITO/WS-CuPc/NPB/Be(PP)₂/LiF/Al的蓝色有机发光二极管(OLEDs).研究了WS-CuPc不同旋涂转速对器件性能的影响.并在WS-CuPc最佳旋涂转速的基础上,进一步研究了WS-CuPc薄膜不同退火方式对器件性能的影响.实验中,对WS-CuPc层采用了一种新的退火方式,即对ITO玻璃衬底先加热后旋涂WS-CuPc层,并与传统退火方式 关键词： 水溶性CuPc 蓝色有机电致发光 旋涂转速 退火方式     

Simulation study of blue InGaN multiple quantum well light-emitting diodes with different hole injection layers

InGaN-based light-emitting diodes with p-GaN and p-AlGaN hole injection layers are numerically studied using the APSYS simulation software.The simulation results indicate that light-emitting diodes with p-AlGaN hole injection layers show superior optical and electrical performance,such as an increase in light output power,a reduction in current leakage and alleviation of efficiency droop.These improvements can be attributed to the p-AlGaN serving as hole injection layers,which can alleviate the band bending induced by the polarization field,thereby improving both the hole injection efficiency and the electron blocking efficiency.     

Effects of hole injection layer thickness on the luminescent properties of white organic light-emitting diodes

This work investigates how the thickness of the hole injection layer (HIL) influences the luminescent characteristics of white organic light-emitting diodes (WOLED). Experimental results indicate that inserting a thin HIL (<200 Å) into a WOLED without an HIL reduces the brightness and clearly changes the chromaticity because the surface of the 4,4′,4″-tris{N,-(3-methylphenyl)-N-phenylamino}-triphenylamine) (m-MTDATA) film is extremely rough. In contrast, a dense film structure and the fine surface morphology of m-MTDATA of moderate thickness (350-650 Å) provides a uniform conducting path on which holes cross the indium tin oxide (ITO)/HIL interface, improving luminescent performance, associated with the relatively stable purity of the color of the emission, with Commission Internationale 1′Eclairage (CIE) coordinates of (x = 0.40, y = 0.40). However, inserting a thick HIL (>650 Å) reduces the luminescent performance and causes red-shift, because the holes and electrons in the effective emissive confinement region become less optimally balanced. Moreover, optimizing the device structure enables a bright WOLED with CIE coordinates of (x = 0.34, y = 0.33) to reach a luminance of 7685 cd/m² at a current density of 100 mA/cm², with a maximum luminous efficiency of 1.72 lm/W at 5.5 V.     

Improving efficiency of organic light-emitting devices by optimizing the LiF interlayer in the hole transport layer

The efficiency of organic light-emitting devices (OLEDs) based on N,N'-bis(1-naphthyl)-N,N'-diphenyl-N,1'-biphenyl-4,4'-diamine (NPB) (the hole transport layer) and tris(8-hydroxyquinoline) aluminum (Alq₃) (both emission and electron transport layers) is improved remarkably by inserting a LiF interlayer into the hole transport layer. This thin LiF interlayer can effectively influence electrical performance and significantly improve the current efficiency of the device. A device with an optimum LiF layer thickness at the optimum position in NPB exhibits a maximum current efficiency of 5.96 cd/A at 215.79 mA/cm², which is about 86% higher than that of an ordinary device (without a LiF interlayer, 3.2 cd/A). An explanation can be put forward that LiF in the NPB layer can block holes and balance the recombination of holes and electrons. The results may provide some valuable references for improving OLED current efficiency.     

Performance improvement of GaN-based light-emitting diode with a p-InAIGaN hole injection layer

The characteristics of a blue light-emitting diode （LED） with a p-InA1GaN hole injection layer （HIL） is analyzed numerically. The simulation results indicate that the newly designed structure presents superior optical and electrical performance such as an increase in light output power, a reduction in current leakage and alleviation of efficiency droop. These improvements can be attributed to the p-InA1GaN serving as hole injection layers, which can alleviate the band bending induced by the polarization field, thereby improving both the hole injection efficiency and the electron blocking efficiency.     

Performance improvement of blue InGaN light-emitting diodes with a specially designed n-AlGaN hole blocking layer

Blue InGaN light-emitting diodes (LEDs) with a conventional electron blocking layer (EBL), a common n-AlGaN hole blocking layer (HBL), and an n-AlGaN HBL with gradual Al composition are investigated numerically, which involves analyses of the carrier concentration in the active region, energy band diagram, electrostatic field, and internal quantum efficiency (IQE). The results indicate that LEDs with an n-AlGaN HBL with gradual Al composition exhibit better hole injection efficiency, lower electron leakage, and a smaller electrostatic field in the active region than LEDs with a conventional p-AlGaN EBL or a common n-AlGaN HBL. Meanwhile, the efficiency droop is alleviated when an n-AlGaN HBL with gradual Al composition is used.     

Tandem organic light-emitting diode with a molybdenum tri-oxide thin film interconnector layer

A 10-nm-thick molybdenum tri-oxide(MoO3) thin film was used as the interconnector layer in tandem organic lightemitting devices(OLEDs).The tandem OLEDs with two identical emissive units consisting of N,N-bis(naphthalen-1-yl)N,N-bis(phenyl)-benzidine(NPB) /tris(8-hydroxyquinoline) aluminum(Alq3) exhibited current efficiency-current density characteristics superior to the conventional single-unit devices.At 20 mA/cm2,the current efficiency of the tandem OLEDs using the interconnector layers of MoO3 thin film was about 4.0 cd/A,which is about twice that of the corresponding conventional single-unit device(1.8cd/A).The tandem OLED showed a higher power efficiency than the conventional single-unit device for luminance over 1200cd/m2.The experimental results demonstrated that a MoO3 thin film with a proper thickness can be used as an effective interconnector layer in tandem OLEDs.Such an interconnector layer can be easily fabricated by simple thermal evaporation,greatly simplifying the device processing and fabrication processes required by previously reported interconnector layers.A possible explanation was proposed for the carrier generation of the MoO3 interconnector layer.     

Non-doped phosphorescent white organic light-emitting devices with a quadruple-quantum-well structure

Non-doped white organic light-emitting devices (WOLEDs) with a quadruple-quantum-well structure were fabricated. An alternate layer of ultrathin blue and yellow iridium complexes was employed as the potential well layer, while potential barrier layers (PBLs) were chosen to be 2,2',2''-(1,3,5-benzenetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) or N,N'-dicarbazolyl-3,5-benzene (mCP) combined TPBi. On adjusting the PBLs for device performance comparison, the results showed that the device with all-TPBi PBLs exhibited a yellow emission with the color coordinates of (0.50,0.47) at a luminance of 1000 cd/m², while stable white emission with the color coordinates of (0.36,0.44) was observed in the device using mCP combined TPBi as the PBLs. Meanwhile, for the WOLED, with a reduced efficiency roll-off, a maximum luminance, luminous efficiency, and external quantum efficiency of 12,610 cd/m², 10.2 cd/A, and 4.4%, respectively, were achieved. The performance improvement by the introduction of mCP PBL was ascribed to the well confined exciton and the reduced exciton quenching effect in the multiple emission regions.     

使用PTB7作为阳极修饰层提高有机发光二极管的性能

采用poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl][3-?uoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]](PTB7)作为有机发光二极管器件的阳极修饰层,制备了结构为indium tin oxide(ITO)/PTB7(不同浓度)/N,N’-Bis(naphthalen-1-yl)-N,N’-bis(phenyl)benzidine(NPB,40 nm)/8-hydroxyquinoline(Alq3,60 nm)/LiF(1 nm)/Al的系列器件,同时研究了不同浓度的PTB7对器件性能的影响.PTB7的最佳浓度为0.25 mg/mL,器件性能得到明显的改善,起亮电压为4.3 V.当驱动电压为14.6 V时,最大亮度为45800 cd/m2,最大电流效率为9.1 cd/A.与没有PTB7修饰的器件相比,其起亮电压降低了1.9 V,最高亮度提升了78.5%.器件性能提高归因于PTB7的插入使得空穴注入和传输能力大大改善.     

Improving the color purity and efficiency of blue organic light-emitting diodes (BOLED) by adding hole-blocking layer

This work demonstrates the fabrication of a bright blue organic light-emitting diode (BOLED) with good color purity using 4,4′-bis(2,2-diphenylvinyl)-1,1′-biphenyl (DPVBi) and bathocuproine (BCP) as the emitting layer (EML) and the hole-blocking layer (HBL), respectively. Devices were prepared by vacuum deposition on indium tin oxide (ITO)-glass substrates. The thickness of DPVBi used in the OLED has an important effect on color and efficiency. The blue luminescence is maximal at 7670 cd/m² when 13 V is applied and the BCP thickness is 2 nm. The CIE coordinate at a luminance of 7670 cd/m² is (0.165, 0.173). Furthermore, the current efficiency is maximum at 4.25 cd/A when 9 V is applied.     

基于红色荧光染料3-(dicyanomethylene)-5, 5-dimethyl-1-(4-dimethylamino-styryl) cyclohexene的高性能白色有机电致发光器件

研究了基于红色荧光染料3-（dicyanomethylene）-5, 5-dimethyl-1-（4-dimethylamino-styryl） cyclohexene（DCDDC）的白色有机电致发光器件的性能,分别制备了基于DCDDC超薄层和DCDDC掺杂主体材料的两种器件结构: 1）indium-tin oxide（ITO）/N, N′-diphenyl-N, N′-bis（1-naphthyl-pheny1）-1, 1′-biphenyl-4, 关键词： 有机电致发光器件 白色发光 红色荧光染料 掺杂     

Improved performances in top-emitting organic light-emitting diodes based on a semiconductor zinc oxide buffer layer

Electroluminescence performances are improved by inserting a semiconductor zinc oxide (ZnO) buffer layer into the emissive tris-(8-hydroxyquinoline)aluminum (Alq₃) layer and the semitransparent Al/Ag cathode in top-emitting organic light-emitting diodes (TEOLEDs) with structures of Si/SiO₂/Ag/Ag₂O/4,4′, 4″-tris(3- methylphenylphenylamino)triphenylamine/ 4,4′-bis[N-(1-naphthyl-1-)-N-phenyl- amino]-biphenyl/Alq₃/ZnO/Al/Ag. The thermal deposition of ZnO layer onto Alq₃ results in Alq₃ anion formation, which is beneficial to electron injection by generating some new energy levels in the forbidden band of Alq₃. In addition, a large hole-injection barrier of 2 eV at the interface of Alq₃/ZnO effectively blocks hole injection into Al/Ag cathode, leading to more carrier recombination in the emissive region.     

Numerical analysis of the mechanism of carrier transport in organic light—emitting devces

The mechanism of carrier transport in organic light-emitting devices is numerically studied,on the basis of trappedcharge-limited conduction with an exponential trap distribution.The spatial distributions of the electrical potential,field and carrier density in the organic layer are calculated and analysed.Most carriers are distributed near the two electrodes,only a few of them are distributed over the remaining part of the orgaic layer,The carriers are accumulated near the electrodes,and the remaining region is almost exhausted of carriers.When the characteristic energy of trap distribution is greater than 0.3eV.it leads to a reduction of current density.In order to improve the device efficiency,organic materials with minor traps and low characteristic energy should be chosen.The diffusion current is the dominant component near the injection electrode.whereas the drift current dominates the remaining region of the organic layer.