Electron Injection Enhancement by Diamond-Like Carbon Film in Polymer Electroluminescence Devices

用正丁胺作碳源,采用射频辉光等离子系统制备类金刚石碳膜(DLC),沉积在聚合物发光器件中的发光层(MEH-PPV)和铝(Al)阴极间作电子注入层.制备了结构为ITO/MEH-PPV/DLC/Al的不同DLC厚度的器件,测量了器件的I-V特性、亮度及效率,研究了DLC层对器件电子注入性能影响的机制.结果表明:当DLC厚度小于1.0nm时,其器件有较ITO/MEH-PPV/Al高的启动电压和低的发光效率;当DLC厚度在1.0～5.0nm之间时,器件的性能随着DLC厚度增加而变好;当DLC厚度为5.0nm时,器件具有最低的启动电压与最高的发光效率;当DLC厚度继续增加时,器件的性能随着DLC厚度增加而变差.并对ITO/MEH-PPV/DLC/Al和ITO/MEH-PPV/LiF/Al的器件性能进行了比较研究.     

LiF作电子注入缓冲层对有机电致发光器件电容的影响

已经有多种方法分析了LiF作为电子注入缓冲层对有机电致发光器件的影响,用LiF/Al双层阴极和发光层Alq3制成的有机电致发光器件(OLED),可以降低器件的开启电压,提高器件的发光效率、发光亮度。文章主要对OLEDs(A):Al/Alq3/ITO和(B):Al/LiF(1nm)/Alq3/ITO的C-V特性进行了研究,当在阴极和发光层Alq3之间加上1nm厚的LiF层作为电子注入缓冲层以后,器件的电容由不加LiF时的72500pF减小到12500pF,由于电容的减小,有效地降低了器件的功耗,进而提高了器件的寿命,节约了能源,进一步改善了器件的性能。     

空穴注入层2T-NATA对OLED器件性能的影响

为了提高有机电致发光器件OLED的发光效率,引入2T-NATA作为空穴注入层,制备了结构为ITO/2T-NATA(Xnm)/NPB(25nm)/Alq3:C545T(20nm:质量分数4.5%)/Alq3(30nm)/LiF(1nm)/Al(100nm)的绿光器件,其中X为空穴注入层2T-NATA厚度。分析了2T-NATA的蒸镀厚度分别0,5,10,15,20,25,30,35nm时器件的发光性能。结果表明,2T-NATA的HOMO能级较好的与ITO功函数匹配,降低了空穴注入势垒,引入空穴注入层2T-NATA提高了器件的发光亮度和效率。当2T-NATA厚度为15nm时,器件的效果最好,起亮电压只需2.87V,亮度最高达到18000cd/m2,是不引入空穴注入层亮度的5倍多,在12V时发光效率可达11.4cd/A。     

不同荧光蓝光层厚度的OLED的制备与光电性能

采用蓝色荧光材料1p-TDPVBi结合绿色磷光材料2Ir(ppy)3掺杂到母体材料CBP作为绿光发光层,并且采用3BPhen作为电子传输层和激子阻挡层制备结构为ITO/m-MTDATA(50nm)/NPB(10nm)/p-TDPVBi(dnm)/CBP∶Ir(ppy)38%7nm/BPhen(60nm)/LiF(1nm)/Al的有机发光器件。实验结果表明:通过改变蓝光发光层p-TDPVBi的厚度,得到了高效率的有机发光器件,当p-TDPVBi厚度为5nm时,器件的电流效率和功率效率在4V时达到32.3cd/A和25.3lm/W,亮度在11V时达到31 020cd/m2。研究了p-TDPVBi厚度由3nm变化到9nm,OLED器件的电流密度-电压特性曲线、亮度-电压曲线及电流效率-电压和功率效率-电压等光电性能的变化。     

用ZnS薄膜作为空穴缓冲层的高效率有机发光二极管

用磁控溅射方法制备的ZnS薄膜作为有机发光器件(OLEDs)的空穴缓冲层,使典型结构的 OLEDs(ITO/TPD/Alq/LiF/Al) 的发光性能得到改善.ZnS 缓冲层厚度对器件性能影响的实验结果表明,当ZnS缓冲层厚度为 5 nm 时,器件的亮度增加了2倍多;当ZnS缓冲层厚度为5、10 nm时,器件的发光电流效率增加40%.研究结果表明 ZnS 薄膜是一种好的缓冲层材料,它能够提高器件的发光效率,改善器件的稳定性.     

基于CdSe/ZnS和Alq3的白光量子点LED的研究

采用CdSe/ZnS红光量子点(QD),利用旋涂和真 空蒸镀工艺制备了结构为ITO/TPD+PVK/QDs/Alq₃/LiF/Al的量 子点发光器件(QD-LED),并对器件的发光性能做了测试。研究了ITO表面处理、TPD空穴 传输层和QD发光层的厚 度对QD-LED性能的影响,并通过调整QD发光层和Alq₃电子传输层的 厚度,制备了可用于照明 的白光QD-LED。实验结果表明,ITO的表面处理可有效降低器件的开启电压,开启 电压从9V降到7V左右; TPD空穴传输层和QD发光层的厚度对器件的电流密度和发光亮度有较大的影响,而Alq₃电 子传输层和QD发光层 的合理配比可以混合出较高色温的白光。通过优化器件各参数,当TPD和PVK质量比为5∶1、QD度为1.0mg/ml和 Alq₃厚为60nm时,制备的器件在15V电压 时发光效率达到了1500c d/m²,色坐标为(0.3628,0.3796) ,显色指数为88.1。     

电子传输层厚度对LiBq4蓝色有机电致发光器件的影响

制备了以LiBq4为发光层,结构为ITO/CuPc/TPD/LiBq4/Alq3/LiF/Al的器件.器件的电致发光(EL)光谱与LiBq4薄膜的光致发光(PL)光谱相同,峰值波长均为492nm.改变电子传输层Alq3的厚度时,器件的电流-电压特性及发光光谱随之发生变化,当电子传输层的厚度为5nm时,既可以避免电子传输层的发光,又可以降低器件的工作电压.     

有机电荷产生层对叠层磷光OLED器件性能的影响

采用C60/pentanece作为非掺杂电荷产生层,并在其两边各插入Al和MoOs薄层作为C60和pentanece的电子注入层和空穴注入层,在此基础上制备了结构为ITO/NPB/mCP∶8wt％Ir (ppy) 3/TPBi/Al/C60/pentanece/MoOs/NPB/mCP∶8wt％Ir (ppy) 3/TPBi/Cs2CO3/Al的双发光单元叠层绿色磷光有机发光器件(OLED).实验表明,增加Al和MoO3电荷注入层,可有效改善有机电荷产生层的电荷注入能力,提高叠层OLED器件的发光亮度和电流效率.叠层器件的启亮电压明显低于单个器件的1/2,但电流效率是单层器件的两倍以上.当Al/C60/pentanece/MoO3的厚度分别是3、15、25和1 nm时,叠层OLED器件具有最佳的光电性能,其最大亮度和最大电流效率分别是7 920.0 cd/m2和16.4 cd/A.     

有机-无机复合薄膜电致发光器件中势垒对光电性能的影响

利用无机非晶SiO2与有机聚合物PPV复合制备了异质结器件,研究了不同层之间由于能级匹配而产生的势垒对整个器件的光电性能的影响。对于单层有机器件ITO/PPV/Al及双层有机无机复合器件ITO/PPV/SiO2/Al,空穴的注入取决于ITO/PPV界面的势垒,空穴是多数载流子,发光强度主要取决于电子的注入。单层器件电子的注入能力与PPV/Al界面的势垒有关;双层器件由于引进SiO2层,提高了电子的注入能力,其发光强度和发光效率较单层器件都有改善。对于3层有机-无机复合器件ITO/SiO2/PPV/SiO2/Al,在两个方向上电子注入的势垒不同,电子的注入能力有所差别,交流激发时,当Al电极为负(ITO为正)时,器件的最大瞬时发光强度是当ITO电极为负(Al为正)时最大瞬时发光强度的1.3倍。     

LiF层对ITD/Alq~3/LiF∶Al器件性能的影响

分别制备了4种有机电致发光器件(OLEDs):ITO/Alq3/Al;ITO/Alq3/LiF(1.0nm):Al;ITO/Alq3/LiF(1.5nm)∶Al;ITO/Alq3/LiF∶(2.0nm)Al。研究了LiF的引入对金属电极与发光层界面的影响以及各种不同的界面态对器件发光性能的影响。研究结果表明:适当的LiF厚度的引入不仅可以改善器件的界面特性,而且可以提高器件的发光亮度及发光效率。     

Effect of Al:Ag alloy cathode on the performance of transparent organic light-emitting devices

Transparent organic light-emitting devices (TOLEDs) based on a stacked alloy cathode of LiF/Al:Ag are investigated. The devices have a structure of indium-tin-oxide (ITO)/4,4′,4′′-Tris[2-naphthyl(phenyl)amino]triphenylamine (2T-NATA) (25 nm)/N,N''-Di-[(1-naphthyl)-N,N''-diphenyl]-1,1''-biphenyl-4,4''-diamine (NPB) (40 nm)/tris-(8-hydroxyquinoline) aluminum (Alq3) (50 nm)/LiF (1 nm)/Al:Ag (1:3) (x), where the thicknesses of cathode metal layers (Al:Ag) are adjusted, respectively, from 70 nm to 100 nm. In the experiment, it is found that the LiF (1 nm)/Al:Ag (1:3) (75 nm) has good electron injection efficiency. Compared with an Al-only cathode, the turn-on voltage is lowered. At the voltage of 10 V, the luminances for bottom emission from ITO anode side and top emission from metal cathode side are 2 459 cd/m2 and 1 729 cd/m2, respectively. Thanks to electron injection enhancement by using Al:Ag cathode, we can obtain a better energy level matching between the cathode and the organic layer, thus the devices have lower turn-on voltage and higher luminance. The total transmittance of the devices can achieve about 40% at the wavelength of 550 nm.     

有机/聚合物异质结电致发光器件的光电性能

器件结构是影响有机发光器件(OLED)性能的重要因素之一.采用8-hydroxyquinoline-aluminum(AlQ)作为发光层(EML)和电子传输层(ETL),polyvinylcarbazole (PVK)作为空穴传输层(HTL),制备了具有有机小分子/聚合物异质结结构的OLED器件,通过其电压-电流-发光亮度(V-J-B)特性测试,研究了HTL的引入及其膜厚对器件性能的影响.实验结果表明,HTL的引入有效地改善了OLED的光电性能,同时HTL膜厚对器件性能具有显著影响,当HTL膜厚为20 nm时,所制备的OLED器件具有最小的驱动电压和启亮电压、最大的发光亮度和发光效率.

Abstract：

The device construction plays an important role in improving the optoelectronic performance of organic electroluminescence devices (OLEDs). Heterojunction OLEDs with a configuration of glass/ITO/PVK/AlQ/Mg/Al were fabricated by using 8-hydroxyquinoline-aluminum (AlQ) as the emission layer (EML) and electron transport layer (ETL) and polyvinylcarbazole (PVK) as the hole transport layer (HTL). The effect of the HTL thickness on the performance of OLEDs was investigated with respect to the driving voltage, turn-on voltage, electroluminescence brightness and efficiency of the devices. Experimental results demonstrate that the optical and electrical properies of OLEDs are closely related to the HTL thickness. The device fabricated with the HTL thickness of 20 nm possesses the best photoelectric properties such as the minimum driving voltage and turn-on voltage, and the maximum electroluminescence brightness and efficiency.     

Enhancement of electron injection in inverted bottom-emitting organic light-emitting diodes using Al/LiF compound thin film

The inverted bottom-emitting organic light-emitting devices (IBOLEDs) were prepared, with the structure of ITO/Al (x nm)/LiF (1 nm)/Bphen (40 nm)/CBP: GIr1 (14%):R-4b (2%) (10 nm)/BCP (3 nm)/CBP:GIr1 (14%):R-4b (2%) (20 nm)/TCTA (10 nm)/NPB (40 nm)/MoO3 (40 nm)/Al (100 nm), where the thickness of electron injection layer Al (x) are 0 nm, 2 nm, 3 nm, 4 nm and 5 nm, respectively. In this paper, the electron injection condition and luminance properties of inverted devices were investigated by changing the thickness of Al layer in Al/LiF compound thin film. It turns out that the introduction of Al layer can improve electron injection of the devices dramatically. Furthermore, the device exerts lower driving voltage and higher current efficiency when the thickness of electron injection Al layer is 3 nm. For example, the current efficiency of the device with 3-nm-thick Al layer reaches 19.75 cd·A^-1 when driving voltage is 7 V, which is 1.24, 1.17 and 17.03 times larger than those of the devices with 2 nm, 4 nm and 5 nm Al layer, respectively. The device property reaches up to the level of corresponding conventional device. In addition, all inverted devices with electron injection Al layer show superior stability of color coordinate due to the adoption of co-evaporation emitting layer and BCP spacer-layer, and the color coordinate of the inverted device with 3-nm-thick Al layer only changes from (0.580 6, 0.405 6) to (0.532 8, 0.436 3) when driving voltage increases from 6 V to 10 V.     

以Ta2O5为电子加速层的MEH-PPV的发光

以Ta2O5为加速层,制备了结构为ITO/Ta2O5/MEH-PPV/Ta2O5/Al的电致发光(EL)器件.通过对器件的EL特性、发光波形随驱动电压变化关系等的研究发现,器件的发光性质和发光机理与固态类阴极射线发光现象一致.研究结果表明,固态类阴极射线发光是一种普遍现象,用具有加速电子能力的Ta2O5作为加速层的EL...     

具有新型空穴缓冲层材料TiO2的有机薄膜发光器件

以溶胶凝胶法制备的TiO2作为空穴缓冲层．在结构为ITO／TiO2／NPB／Alq／LiF／A1的器件中,改善了器件的发光效率。研究了TiO2厚度对器件发光特性的影响。在电流密度为100mA／cm^3时,有缓冲层的器件发光效率为5cd／A,而没有缓冲层的器件发光效率为3．45cd／A,有TiO2缓冲层的器件发光效率有了明显提高。     

Improved polymer light-emitting diodes by the tuning of charge balance

We have prepared polymer-small molecule hybrid electroluminescence devices with improved brightness and efficiency by a doping method. The doping effect on the hole transporter N,N′-diphenyl-N,N′-bis(4′-[N,N-bis(naphth-1-yl)-amino]-biphenyl-4-yl)-benzidine has been investigated in bilayer devices with structure of ITO/MEH-PPV: TPTE/PBD/Al. It was found that the effective hole mobility increases with increasing TPTE content in the blend, which is directly determined by space charge limited current at high voltage. The brightness and EL efficiencies of the doped OLEDs were increased significantly over those obtained for devices based only on MEH-PPV, which is attributed to more balanced electron and hole recombination due to improved hole mobility.     

Pure and Saturated Red Electroluminescent Polyfluorenes with Dopant/Host System and PLED Efficiency/Color Purity Trade‐Offs

Three kinds of red electroluminescent (EL) polymers based on polyfluorene as blue host and 2,1,3‐benzothiadiazole derivatives with different emission wavelengths as red dopant units on the side chain are designed and synthesized. The influence of the photoluminescence (PL) efficiencies and emission wavelengths of red dopants on the EL efficiencies and color purities of the resulting polyfluorene copolymers of dopant/host system is investigated by adjusting the electron donating ability of the donor units in D‐π‐A‐D typed 2,1,3‐benzothiadiazole derivatives. The devices of these red‐emitting polymers realize remarkable EL efficiency/color purity trade‐offs. The single‐layer devices with the configuration of ITO/PEDOT:PSS/Polymer/Ca/Al show pure red emission at 624 nm with a luminous efficiency of 3.83 cd A^?1 and CIE of (0.63, 0.35) for PFR1, saturated red emission at 636 nm with a luminous efficiency of 2.29 cd A^?1 and CIE of (0.64, 0.33) for PFR2, respectively. By introduction of an additional electron injection layer PF‐EP(Ethanol soluble phosphonate‐functionalized polyfluorene), high performance pure and saturated red emission two‐layer devices (ITO/PEDOT:PSS/Polymer/PF‐EP/LiF/Al) were achieved with maximum luminous efficiencies of 5.50 cd A^?1 and CIE of (0.62, 0.35) for PFR1, 3.10 cd A^?1 and CIE of (0.63, 0.33) for PFR2, respectively, which are the best results for pure and saturated fluorescent red EL polymers reported so far.     

Study of organic solar cells with stacked bulk heterojunction structure

Organic solar cells with stacked bulk heterojutaction（BHJ） are investigated based on conjugated polymer. By using the solution spin-coating method, Poly[2-methoxy, 5-（2＇ -ethyl-hexyloxy） -1,4-phenylene vinylene] （MEH-PPV） and ZnO nanoparticles （50 nm） are mixed as the optical sense layer. Ag is used as inter-layer to connect the upper BHJ cell and the lower cell. The structures are ITO/PEDOT：PSS/MEH-PPV lAg / MEH-PPV：ZnO/Al. The open circuit voltage （Voc） of a stacked cell is about 3.7 times of that of an individual organic solar cell （ITO/PEDOT：PSS/MEH-PPV/Al）. The short circuit current （Jsc） of a stacked cell is increased by about 1.6 times of that of individual one.