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     

高效率的有机电致发光器件

有机电致发光器件 (OL EDs)的发光机理包括电子和空穴从电极的注入、激子的形成及复合发光 ,其中 ,空穴和电子的注入平衡是非常重要的。为了平衡载流子的注入以得到高效率和稳定性好的器件 ,人们不仅使用了电子注入更为有效的 L i F/ Al[1] 和 Cs F/ Al[2 ] 等复合电极 ,同时也使用了空穴缓冲层 ,如 S.A.Van Slyke等 [3]在ITO和 NPB之间使用 Cu Pc,使得器件的稳定性得到了明显的提高 ;A.Gyoutoku等[4 ] 用碳膜使器件的半寿命超过 3 5 0 0小时 ;最近 ,Y.Kurosaka等 [5]和 Z.B.Deng[6 ]分别在 ITO和空穴传输层之间插入一薄层 Al…     

利用p型掺杂技术制备的高效有机电致发光器件

利用氧化钼(MoO_x)作为p型掺杂剂,以掺杂层4,4'-bis(carbazol-9-yl)biphenyl(CBP):MoO_x作为空穴注入层,制备了一种结构为ITO/MoO_x/CBP:MoO_x/CBP/CBP:tris(2-phenylpyridine)iridium(III)(Ir(ppy)₃)/4,7-diphenyl-1,10-phenanthroline(Bphen)/LiF/Al的有机电致发光器件.器件中CBP同时作为空穴注入层、空穴传输层以及发光层母体材料,这种结构具有结构简单同时能有效降低空穴注入势垒等优点.研究发现,随着空穴注入层厚度的增加,器件的电流密度增加,表明p型掺杂层的引入能够有效增强空穴的注入;通过优化器件空穴注入层与空穴传输层厚度,器件性能有所提高,最大电流效率为29.8 cd/A,可以认为合理的优化空穴注入层和空穴传输层的厚度,使载流子在发光层中的分布更加平衡是提高器件发光效率的主要原因.值得指出的是,从电流效率最大值到亮度为 20 000 cd/m²时,优化后器件的效率衰减仅为17.7%,而常规器件的效率衰减则为62.1%,优化后器件效率衰减现象得到了明显的改善.分析认为优化后的器件中未掺杂的CBP有助于展宽激子形成区宽度,进而减弱了三线态-三线态湮灭、三线态-极化子淬灭现象,激子形成区的展宽是改善效率衰减的主要原因.     

空穴传输层对有机电致发光器件性能的影响

制备了结构为ITO/MoO₃(40 nm)/空穴传输层/CBP:Ir(ppy)₂acac(8%)(30 nm)/BCP(10 nm)/Alq₃(40 nm)/LiF(1 nm)/Al(100 nm)的器件,其中Ir(ppy)₂acac为绿色磷光染料,空穴传输层分别为TAPC(50 nm)、TAPC(40 nm)/TCTA(10 nm)、NPB(50 nm)、NPB(40 nm)/TCTA(10 nm)。通过使用4种不同结构的空穴传输层,对器件的发光性能进行了研究。结果表明,空穴传输层对器件的发光性能有较大影响。在电压为6 V、电流密度为2 mA/cm²的条件下,4种结构的器件的电流效率分别为52.5,67.8,35.6,56.6 cd/A。其原因是TAPC/TCTA及NPB/TCTA能级结构更有利于空穴对发光层的注入而且TAPC拥有较高的空穴迁移率;另外,TAPC及TCTA拥有较高的LUMO和三线态能量,可以有效地将电子和三线态激子束缚在发光层内,增加绿光染料的复合发光几率。所制备的器件均表现出良好的色坐标稳定性。     

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.     

Highly efficient and stable organic light-emitting diode by balancing drift current of charge

Highly efficient and stable OLED device in which hole-drift current and electron-drift current are balanced was fabricated. Drift current characteristics according to the thickness of organic layer were examined using the device with ITO/m-MTDATA/NPB/Al structure that can only move the hole and the device with Al/LiF/Alq₃/LiF/Al structure that can only move the electron. Using the result of such examination, green device with balanced drift current was produced. Device with the structure of m-MTDATA (80 nm)/NPB (20 nm)/C-545T (3%) doped Alq₃ (5 nm)/Alq₃ (59 nm)/LiF (1 nm)/Al (200 nm) showed color purity of (0.309, 0.643) and high efficiency of 7.0 lm/W (14.4 cd/A). Most of light emission was observed inside the green emitting layer. Through the result of EL spectrum for the device also including red emitting layer, same result could be obtained. The device with balanced drift current also showed half life-time of 175 h for initial luminance of 3000 cd/m², which is more stable in comparison to the device without balanced drift current.     

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.     

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.     

Highly efficient and stable organic light-emitting diodes employing MoO3-doped perylene-3, 4, 9, 10-tetracarboxylic dianhydride as hole injection layer

We report highly efficient and stable organic light-emitting diodes (OLEDs) with MoO₃-doped perylene-3, 4, 9, 10-tetracarboxylic dianhydride (PTCDA) as hole injection layer (HIL). A green OLED with structure of ITO/20 wt% MoO₃: PTCDA/NPB/Alq₃/LiF/Al shows a long lifetime of 1012 h at the initial luminance of 2000 cd/m², which is 1.3 times more stable than that of the device with MoO₃ as HIL. The current efficiency of 4.7 cd/A and power efficiency of 3.7 lm/W at about 100 cd/m² have been obtained. The charge transfer complex between PTCDA and MoO₃ plays a decisive role in improving the performance of OLEDs.     

富勒烯掺杂NPB空穴传输层的有机电致发光器件

报道了不同掺杂浓度NPB：C₆₀（富勒烯）作为空穴传输层对有机电致发光器件性能的影响.采用真空热蒸镀方法,制作了ITO/ NPB：C₆₀ （x % ）/Alq₃/LiF/Mg:Ag结构的四种有机电致发光器件.当NPB：C₆₀的掺杂浓度是15％时,器件的启亮电压是4 V,最大亮度是11000 cd/m².然而,当NPB：C₆₀的掺杂浓度是20％时,器件的最大亮度降     

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...     

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)。     

水溶性酞菁化合物对有机电致发光器件亮度和效率的影响

以水溶性酞菁铜(CuTcPc)为空穴注入层制备多层有机电致发光器件.ITO表面经过CuTcPc溶液修饰,能够提高空穴的注入能力,增加器件的电流密度和亮度.在有机电致发光器件中,空穴传输材料的空穴迁移率一般大于电子传输材料的电子迁移率,空穴是多数载流子;但是,CuTcPc修饰处理不仅提高了器件的电流密度和亮度,也提高了器...     

High-efficiency Simple Structure White Organic Light-emitting Devices Based on Rubrene Ultrathin Layer

White organic light-emitting devices (WOLEDs) were fabricated with an ultrathin layer of rubrene inserted between NPB and TPBI. With a simple three-layer structure of ITO/NPB(50 nm)/rubrene(0.1 nm)/TPBI(50 nm)/LiF/Al, a white light with CIE coordinates of (0.31, 0.30) were generated. The device gave a maximum luminance efficiency of 2.04 lm/W at 5 V. Furthermore, with a multilayer structure of ITO/m-MTDATA(30 nm)/NPB(20 nm)/rubrene(0.1 nm)/TPBI(40 nm)/Alq₃(10 nm)/LiF/Al, the device reached a maximum luminance efficiency of 4.29 lm/W at 4 V and the luminance could exceed 10 000 cd/m² at 10 V.     

基于载流子平衡的效率及亮度提高的有机蓝光器件

研究了在两空穴传输层之间插入Bphen中间层对有机蓝光器件(BOLEDs)效率的影响。结果表明,其对空穴的阻挡作用使得电子与空穴在发光区内达到相对平衡,减少了激子-极化子猝灭几率,从而提高了有机蓝光器件的效率和亮度。器件的最大电流效率从16.12 cd/A增加到20.52 cd/A,相对提高了27.30%;最大功率效率从14.23 lm/W增加到17.64 lm/W,相对提高了23.96%。文中对提高效率的物理机制进行了详细的阐述。     

新型苯乙烯衍生物掺杂的蓝色及白色有机电致发光器件

研究了新型高效蓝色掺杂剂EBDP的电致发光性能. 分别以EBDP为掺杂剂制备了结构为氧化铟 锡(ITO)/酞菁铜(CuPc)/N,N′-二(1-萘基)-N,N′-二苯基-1,1′-联苯-4-4′-二胺(NPB)/2- 叔丁基-9,10-二-(2-萘基)蒽(TBADN):EBDP/8-羟基喹啉铝(Alq₃)/LiF/Al 与ITO /CuPc/NPB/TBADN:EBDP: 4-二氰亚甲基-2-叔丁基-6-(1,1,7,7-四甲基久咯呢定基-9-烯基)- 4H-吡喃/Alq_{3 关键词： 有机电致发光 蓝色掺杂剂 蓝色电致发光器件 白色电致发光器件}     

LiF插层对有机发光二极管磁场效应的调控

制备了有LiF插层的有机发光二极管,以八羟基喹啉铝（Alq₃）作为电子传输层,N, N′-二苯基-N, N′-二(1-萘基)-1,1′-联苯-4,4′-二胺（NPB）作为空穴传输层.通过改变Alq₃与NPB间LiF插层的厚度,研究了不同温度下器件的光电特性及电致发光的磁场效应.测量结果表明:LiF插层可以影响器件内部载流子的输运和激发态的形成.较厚的插层阻碍了空穴的传输,使器件的电流效率变低.但实验中发现, 关键词： LiF插层结构 磁场效应 三重态激子     

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.     

New double graded structure for enhanced performance in white organic light emitting diode

This study presents a new design that uses a combination of a graded hole transport layer (GH) structure and a gradually doped emissive layer (GE) structure as a double graded (DG) structure to improve the electrical and optical performance of white organic light-emitting diodes (WOLEDs). The proposed structure is ITO/m-MTDATA (15 nm)/NPB (15 nm)/NPB: 25% BAlq (15 nm)/NPB: 50% BAlq (15 nm)/BAlq: 0.5% Rubrene (10 nm)/BAlq: 1% Rubrene (10 nm)/BAlq: 1.5% Rubrene (10 nm)/Alq₃ (20 nm)/LiF (0.5 nm)/Al (200 nm). (m-MTDATA: 4,4′,4″ -tris(3-methylphenylphenylamino)triphenylamine; NPB: N,N′-diphenyl-N,N′-bis(1-naphthyl-phenyl)-(1,1′-biphenyl)-4,4′-diamine; BAlq: aluminum (III) bis(2-methyl-8-quinolinato) 4-phenylphenolate; Rubrene: 5,6,11,12-tetraphenylnaphthacene; Alq₃: tris-(8-hydroxyquinoline) aluminum). By using this structure, the best performance of the WOLED is obtained at a luminous efficiency at 11.8 cd/A and the turn-on voltage of 100 cd/m² at 4.6 V. The DG structure can eliminate the discrete interface, and degrade surplus holes, the electron-hole pairs are efficiently injected and balanced recombination in the emissive layer, thus the spectra are unchanged under various drive currents and quenching effects can be significantly suppressed. Those advantages can enhance efficiency and are immune to drive current density variations.     

多层结构的阴极修饰层对有机电致发光器件的性能改善

为提高有机电致发光器件（OLEDs）的阴极电子注入效率,我们设计了新型的阴极杂化修饰层,其结构为Bphen∶LiF/Al/MoO₃,将其应用到器件ITO/NPB/Alq₃/Al中,参考器件的电子注入层选用传统材料LiF。实验研究表明,与传统的阴极修饰层LiF相比,基于这种杂化结构的阴极修饰层非常有效。测试了器件的电致发光光谱（EL谱）,其峰值位于534 nm,发光来自于Alq₃,实验中我们可以观察到明亮的绿色发光。将其与传统参考器件的EL谱进行对比,在电流密度40 mA·cm-2下,两个器件的电致发光光谱是一致的。在0～100 mA·cm-2范围内,对器件的EL谱进行了测试。实验结果表明,随着电流密度的增加,器件的发光增强,但是EL谱的形状和谱峰的位置是固定不变的。与参考器件对比,基于杂化修饰层的器件的发光性能更好。研究表明,杂化修饰层的最佳参数为Bphen∶LiF(5 nm; 6%)/Al(1 nm)/MoO₃(5 nm),在测试范围内,器件的最大电流效率和最大功率效率分别为4.28 cd·A-1和2.19 lm·W-1,相比参考器件提高了25.5%和23.7%。器件的电流密度-电压特性曲线表明阴极杂化修饰层可以增强电子的注入,使器件中的载流子更加平衡,从而提高了器件的发光性能。从两个角度对器件效率的增强进行了理论方面的论证。一方面利用阴极杂化修饰层的作用机制来解释。在HML中,LiF能填充Bphen的电子陷阱,增强电流的注入,同时HML也能限制空穴的传输,减小空穴电流。另一方面从电荷平衡因子的角度,HML增强了电子的注入,使得器件的电荷平衡因子增大,空穴和电子的平衡性更好。实验研究表明,阴极杂化修饰层很好地增强了器件的效率。