发光层和空穴传输层对白色电致发光器件性能的影响

利用电子传输性能良好的苯并噻唑螯合锌(Zn(BTZ)₂)作为蓝光层，通过设计不同类型的空穴传输层并试验不同厚度的发光层后，制作了一种最佳厚度的双发光层白色电致发光器件：氧化铟锡(ITO)/N-N′-双(3-甲基苯基)-N-N′-二苯基-1-1′-二苯基-4-4′-二胺(TPD)∶N,N′-二(1-萘基)-N,N′-二苯基-1,1′-联苯-4-4′-二胺(NPB)(1∶0.0 关键词： 厚度 空穴传输层 白光 载流子     

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 influence of exciton behavior on luminescent characteristics of organic light-emitting diodes

We used N,N′-bis-(1-naphthyl)-N,N′-1-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB), 4,4′-N,N′-dicarbazole-biphenyl (CBP) and tris(8-hydroxyquinoline) aluminum (Alq₃) to fabricate tri-layer electroluminescent (EL) device (device structure: ITO/NPB/CBP/Alq₃/Al). In photoluminescence (PL) spectra of this device, the emission from NPB shifted to shorter wavelength accompanying with the decrease of its emission intensity and moreover the emission intensity of Alq₃ increased relatively with the increase of reverse bias voltage. The blue-shifted emission and the decrease in emission intensity of NPB were attributed to the polarization and dissociation of NPB excitons under reverse bias voltage. The increase of emission intensity of Alq₃ benefited from the recombination of electrons (produced by the dissociation of NPB exciton) and holes (injected from the Al cathode).     

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.     

Improvement of performance of tetraphenylporphyrin-based red organic light emitting diodes using WO3 and C60 buffer layers

One of the porphyrin derivatives, meso-tetraphenylporphyrin (TPP), has been synthesized and examined as an emitter material (EM) for efficient fluorescent red organic light-emitting diodes (OLEDs). By inserting a tungsten oxide (WO₃) layer into the interface of anode (ITO) and hole transport layer N,N′-Di-[(1-napthyl)-N,N′-diphenyl]-(1,1′-biphenyl)-4,4′-diamine (NPB) and by using fullerene (C₆₀) in contact with a LiF/Al cathode, the performance of devices was markedly improved. The current density–voltage–luminance (J–V–L) characterizations of the samples show that red OLEDs with both WO₃ and C₆₀ as buffer layers have a lower driving voltage and higher luminance compared with the devices without buffer layers. The red OLED with the configuration ITO/WO₃ (3 nm)/NPB (50 nm)/TPP (60 nm)/BPhen (30 nm)/C₆₀ (5 nm)/LiF (0.8 nm)/Al (100 nm) achieved the high luminance of 6359 cd/m² at the low driving voltage of 8 V. At a current density of 20 mA/cm², a pure red emission with CIE coordinates of (0.65; 0.35) is observed for this device. Moreover, a power efficiency of 2.07 lm/W and a current efficiency of 5.17 cd/A at 20 mA/cm² were obtained for the fabricated devices. The study of the energy level diagram of the devices revealed that the improvement in performance of the devices with buffer layers could be attributed to lowering of carrier-injecting barrier and more balanced charge injection and transport properties.     

Enhancing properties of organic light-emitting diodes with LiF inside the hole transport layer

A new device has been made by inserting thin LiF layer in N,N′-diphenyl-N,N′-bis(1-napthyl–phenyl)-1, 1′-biphenyl-4,4′-diamine (NPB), which has a configuration of ITO/NPB(20 nm)/LiF(0.5 nm)/NPB(20 nm)/Alq₃(60 nm)/LiF(0.5 nm)/Al. Compared with normal device, the device inserted LiF layer inside NPB (HTL) can improve its performance. The luminance and efficiency is about 1.4 and 1.3 folds high of the conventional structure, respectively. The suggestion mechanism is that the LiF in the NPB layer can block holes of NPB, and balance the holes and electrons. Consequently, there are more excitons formed to boost the diode’s luminance and efficiency. And it may offer some valuable references for OLED’s structure.     

基于ZnSe的有机-无机异质结电致发光器件

以电子束蒸发的方法制备硒化锌(ZnSe)薄膜，研究了基于ZnSe的有机-无机异质结电致发光器件.在双层器件ITO/ZnSe(50nm)/Alq₃(12nm)/Al中看到了峰值位于578nm的ZnSe电致发光，却很难得到单层器件ITO/ZnSe(50—120nm)/Al的电致发光；在此基础上进一步引入有机空穴传输层(HTL)，通过改变器件的结构，讨论了ZnSe对有机-无机异质结器件ITO/HTL/ZnSe/Alq₃/Al电致发光特性的影响.其电致发光光谱的研究结果证实了ZnSe在器件中的作用：ZnSe既起传输电子的作用，也起到传输空穴的作用，还作为发光层.并对ZnSe的发光机理进行了讨论. 关键词： 硒化锌 有机-无机异质结 电致发光 空穴传输层     

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.     

Affect of the electrical characteristics depending on the hole and electron injection materials of red organic light-emitting diodes

This study examined the electrical and optical properties of red OLEDs (organic light-emitting diodes) with a four-layer structure, ITO/amorphous fluoropolymer (AF)/N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1-biphenyl-4,4′-diamine (TPD)/R-H:R-D/lithium fluoride (LiF)/Al, containing a hole injection material, AF (amorphous fluoropolymer) and an electron injection layer material, LiF. Compared to the basic structure (two-layer structure), the brightness and luminous efficiency of the four-layer structure, ITO/TPD/R-H:R-D/Al, increased approximately 100 times (30,000 lm/m²) and 150 times (51 lm/W), respectively, with an applied voltage. The excellent efficiency of the external proton was also increased 150 times (0.51%). That is, the hole and electron injection layers improved the surface roughness of ITO and Al, and the interfacial physical properties. In addition, these layers allowed the smooth injection of holes and electrons. The luminance, luminous efficiency and external quantum efficiency were attributed to an increase in the recombination rates.     

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     

Low driving voltage in organic light-emitting diode using MoO3/NPB multiple quantum well structure in hole transport layer

Driving voltage of organic light-emitting diode (OLED) is lowered by employing molybdenum trioxide (MoO₃)/N, N'-bis(naphthalene-1-yl)-N,N'-bis(phe-nyl)-benzidine (NPB) multiple quantum well (MQW) structure in hole transport layer. For the device with double quantum well (DQW) structure of ITO/ [MoO₃ (2.5 nm)/NPB (20 nm)]₂/Alq₃(50 nm)/LiF (0.8 nm)/Al (120 nm)], the turn-on voltage is reduced to 2.8 V, which is lowered by 0.4 V compared with that of the control device (without MQW structures), the driving voltage is 5.6 V, which is reduced by 1 V compared with that of the control device at the 1000 cd/m². In this work, the enhancement of the injection and transport ability for holes could reduce the driving voltage for the device with MQW structure, which is attributed not only to the reducing energy barrier between ITO and NPB, but also to the forming charge transfer complex between MoO₃ and NPB induced by the interfacial doping effect of MoO₃.     

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     

Enhancement of the efficiency and the color stabilization of organic light-emitting devices fabricated utilizing stepwise doped hole transport layers

The electrical and the optical properties of organic light-emitting devices (OLEDs) consisting of aluminum (Al)/lithium quinolate/tris (8-hydroxyquimoline) Al/5,6,11,12-tetraphenylnaphthacene (rubrene)-doped N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1-biphenyl-4,4′-diamine (NPB)/indium-tin-oxide/glass structures fabricated with uniformly doped and stepwise-doped hole transport layers (HTLs) were investigated. The turn-on voltage of the OLEDs fabricated utilizing a stepwise-doped HTL was smaller than that of the OLEDs fabricated with a uniformly doped HTL, and the corresponding luminance at the same voltage was higher. The Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of the OLEDs fabricated utilizing a stepwise-doped HTL became stabilized, and the CIE chromaticity coordinates of the OLEDs at 12 V was (0.43, 0.53), indicative of a yellow emission corresponding to the rubrene layer. The luminescence mechanisms of the OLEDs fabricated utilizing a stepwise-doped HTL are described on the basis of the experimental results.     

NPB厚度对异质结OLED载流子复合区域的调控

通过调控p型半导体N,N′-bis(naphthalen-1-y)-N,N′-bis(phenyl)benzidine(NPB)层的厚度,制备了结构为ITO/NPB/aluminum(Ⅲ)bis(2-methyl-8-quinolinato)-4-phenylphenolate(BAlq)/NPB(0~18nm)/tri-(8-hydroxyquinoline)-aluminum(Alq₃)/Mg:Ag的多层有机电致发光器件.分析结果表明,在该类异质结器件中,NPB不仅可以作为空穴传输材料,在适当的厚度范围内,它还可以起到调控载流子复合区域的作用;当NPB厚度在0~18nm之间变化时,随着其厚度增加器件发光颜色可由蓝色变为绿色.通过器件发光光谱的表征可以得知,器件的载流子复合区域相应地由BAlq层转移至Alq₃层.     

Blue organic light-emitting diodes with low driving voltage and maximum enhanced power efficiency based on buffer layer MoO3

Blue organic light-emitting devices based on wide bandgap host material, 2-(t-butyl)-9, 10-di-(2-naphthyl) anthracene (TBADN), blue fluorescent styrylamine dopant, p-bis(p-N,N-diphenyl-amino-styryl)benzene (DSA-Ph) have been realized by using molybdenum oxide (MoO₃) as a buffer layer and 4,7-diphenyl-1,10-phenanthroline (BPhen) as the ETL. The typical device structure used was glass substrate/ITO/MoO₃ (5 nm)/NPB (30 nm)/[TBADN: DSA-Ph (3 wt%)](35 nm)/BPhen (12 nm)/LiF (0.8 nm)/Al (100 nm). It was found that the MoO₃∥BPhen-based device shows the lowest driving voltage and highest power efficiency among the referenced devices. At the current density of 20 mA/cm², its driving voltage and power efficiency are 5.4 V and 4.7 Lm/W, respectively, which is independently reduced 46%, and improved 74% compared with those the m-MTDATA∥Alq₃ is based on, respectively. The J-V curves of ‘hole-only’ devices reveal that a small hole injection barrier between MoO₃∥NPB leads to a strong hole injection, resulting low driving voltage and high power efficiency. The results strongly indicate that carrier injection ability and balance shows a key significance in OLED performance.     

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     

Low driving voltage in an organic light-emitting diode using MoO3/NPB multiple quantum well structure in a hole transport layer

The driving voltage of an organic light-emitting diode(OLED) is lowered by employing molybdenum trioxide(MoO3)/N,N’-bis(naphthalene-1-yl)-N,N’-bis(phe-nyl)-benzidine(NPB) multiple quantum well(MQW) structure in the hole transport layer.For the device with double quantum well(DQW) structure of ITO/[MoO3(2.5 nm)/NPB(20 nm)]2/Alq3(50 nm)/LiF(0.8 nm)/Al(120 nm)],the turn-on voltage is reduced to 2.8 V,which is lowered by 0.4 V compared with that of the control device(without MQW structures),and the driving voltage is 5.6 V,which is reduced by 1 V compared with that of the control device at the 1000 cd/m2.In this work,the enhancement of the injection and transport ability for holes could reduce the driving voltage for the device with MQW structure,which is attributed not only to the reduced energy barrier between ITO and NPB,but also to the forming charge transfer complex between MoO3 and NPB induced by the interfacial doping effect of MoO3.     

采用复合空穴注入层提高有机电致发光器件的性能

制备了以Ag/SAM/m-MTDATA为复合空穴注入层的NPB/Alq₃双层异质结发光器件,研究了器件的性能并与传统的器件进行了对比。考察了银膜厚度的变化对器件性能的影响。研究了光谱窄化以及微腔效应对器件的影响。研究结果表明:在ITO表面制备4-FTP自组装单分子膜修饰的5 nm厚的金属银膜,可以在保持阳极透明性的基础上,增强空穴的注入,改善界面的形貌,进而提高器件性能。制备的ITO/Ag/SAM/m-MTDATA/NPB/Alq₃/LiF/Al器件的启亮电压为4 V,最 大电流效率为6.9 cd/A, 最大亮度为34 680 cd/m²(12 V);优于以ITO为阳极的对比器件(25 300 cd/m² @12 V)。     

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.     

Reduction of driving voltage in organic light-emitting diodes with molybdenum trioxide in CuPc/NPB interface

A novel structure of organic light-emitting diode was fabricated by inserting a molybdenum trioxide (MoO₃) layer into the interface of hole injection layer copper phthalocyanine (CuPc) and hole transport layer N,N′-diphenyl-N,N′-bis(1-napthyl-phenyl)-1,1′-biphenyl-4,4′-diamine (NPB). It has the configuration of ITO/CuPc(10 nm)/MoO₃(3 nm)/NPB(30 nm)/ tris-(8-hydroxyquinoline) aluminum (Alq₃)(60 nm)/LiF(0.5 nm)/Al. The current density-voltage-luminance (J-V-L) performances show that this structure is beneficial to the reduction of driving voltage and the enhancement of luminance. The highest luminance increased by more than 40% compared to the device without hole injection layer. And the driving voltage was decreased obviously. The improvement is ascribed to the step barrier theory, which comes from the tunnel theory. The power efficiency was also enhanced with this novel device structure. Finally, “hole-only” devices were fabricated to verify the enhancement of hole injection and transport properties of this structure.