空穴注入层MoO_3厚度对蓝绿色磷光OLED发光特性的影响

以mCP为磷光主体材料,BGIr1为蓝绿色磷光掺杂材料,MoO3为空穴注入材料,制备5种不同厚度的MoO3蓝绿色磷光有机电致发光器件(OLED),并研究不同厚度MoO3空穴注入层对蓝绿色磷光OLED发光特性的影响。所制器件结构为ITO/MoO3(x nm)/NPB(40nm)/mCP∶BGIr1(30nm,18%)/BCP(10nm)/Alq3(20nm)/LiF(1nm)/Al(100nm),其中18%为发光层中BGIr1的掺杂量(质量分数),x为空穴注入层MoO3的厚度。研究结果表明,本实验制备器件空穴注入层MoO3的最佳厚度为20nm。当电压为13V时,MoO3厚度为20nm器件获得最大亮度为8 617cd/cm2,当电流密度为20mA/cm2时,器件获得最大发光效率为5.7cd/A。器件在488和512nm处获得两个主发射峰,发光颜色稳定,CIE坐标为(0.19,0.21)。     

以萘为π-中心的双芪类衍生物的电致发光特性研究

以自制的"D-π-D"对称型有机绿色发光分子1,4-双(4'-N,N-二甲基氨基苯乙烯基)萘(简称 BMABN)为发光层,在结构为ITO/NPB/BMABN/BCP/Mg∶Ag的器件中,研究了空穴阻挡层厚度对器件发光性能的影响.结果表明,空穴阻挡层的增厚使得器件的起亮电压有所增加,但器件的亮度、电流效率和稳定性显著增加.该器件在5V开启,18V电压下亮度和效率分别为2000cd/m2和0.4lm/W.     

主客体掺杂和空穴阻挡对蓝色磷光OLED发光性能的影响研究

以铱配合物蓝色磷光材料Firpic作为掺杂剂,制备了基于CBP为主体的蓝色有机电致发光器件,其结构为ITO/CuPc/FIrpic:CBP(x%)/BCP/Alq3/LiF/Al,其中x%为发光层主客体掺杂浓度.分别研究了主客体掺杂浓度和空穴阻挡层BCP的厚度对器件发光性能的影响,当掺杂浓度为8%时,主客体间的能量传转移最充分,器件的启亮电压为5V,器件在20V时的亮度为7122.25cd/m2.器件电致发光(EL)光谱出现明显的红移现象,为Alq3部分参与了发光,影响了发光的色纯度,改变BCP的厚度,可以调节载流子复合区域和器件发光的色度坐标,达到改善器件发光性能的目的.     

具有双掺杂发射层白光OLED器件结构的研究

白光有机电致发光器件是获得全色器件的基础。制备了一种具有双掺杂发射层的白光OLED器件，其结构为ITO／CuPc／NPB／ADN：TBP以ALQ：DCJTB／ALQ，Mg：Ag，将2，5，8，11-tetra-tertbutylperylen-e（TBPe）掺杂到蓝光主体材料ADN中作为蓝色发光层，4-（dicyanome-thylene）-2-t-butyl-6-（1，1,7，7tetramethyljul-olidyl-9-enyl）-4H-pyran（DCJTB）掺杂到AIQ中作为红色发光层，通过实验结果对比，研究了TBPe以及DCJTB的掺杂浓度对器件性能的影响，确定了当TBPe浓度为3％（质量分数），DCJTB浓度为1．8％（质量分数），时，获得的白光器件性能最优。     

OLED器件空穴传输层中TPBI空穴阻档层的应用研究

针对有机发光器件中普遍存在空穴漏电流影响发光效率的问题,将2nm的TPBI薄层引入到TPD空穴传输层中,改变该薄膜位置考察对器件光电性能的影响.结果表明,引入TPBI薄膜后器件发光效率均有明显提高.其中,当TPBI薄膜距离阳极界面10nm时,器件的最大发光效率为4.89cd/A,相对于没有阻档层的常规器件提高52.3%.同时,器件的电流性能变化明显,随着减小TPBI薄膜与阳极的距离而减小.这说明,TPBI薄膜具备阻挡或者减缓空穴传输的能力,从而减小空穴漏电流,平衡发光层中的载流子并提高发光效率;同时,被阻挡的空穴积累在TPBI界面也将改变器件内的电场分布,从而TPBI位置不同,器件的电场分布也不同,体现为器件的电学性能随之改变.     

OLED器件空穴传输层中TPBI空穴阻挡层的应用研究

针对有机发光器件中普遍存在空穴漏电流影响发光效率的问题,将2nm的TPBI薄层引入到TPD空穴传输层中,改变该薄膜位置考察对器件光电性能的影响。结果表明,引入TPBI薄膜后器件发光效率均有明显提高。其中,当TPBI薄膜距离阳极界面10nm时,器件的最大发光效率为4.89cd/A,相对于没有阻挡层的常规器件提高52.3%。同时,器件的电流性能变化明显,随着减小TPBI薄膜与阳极的距离而减小。这说明,TPBI薄膜具备阻挡或者减缓空穴传输的能力,从而减小空穴漏电流,平衡发光层中的载流子并提高发光效率;同时,被阻挡的空穴积累在TPBI界面也将改变器件内的电场分布,从而TPBI位置不同,器件的电场分布也不同,体现为器件的电学性能随之改变。     

TMEP作为缓冲层增加有机发光器件的效率的研究

在有机发光器件中的发光层和阴极之间插入了稳定性好、有良好电子传输能力的苝酸四甲酯(TMEP)新型缓冲层,改善了有机电致发光器件的亮度和发光效率.在电流密度为200mA/cm2时,有缓冲层的器件B效率为0.82cd/A,没有缓冲层的器件A效率为0.14cd/A.     

芴类有机电致发光器件材料特性的分析

用芴类小分子衍生物材料（BDHFLYD-FLQ）作为电子传输层和发光层制备了OLED器件,考察了BDHFLYDFLQ分子和空穴传输材料（NPB）分子之间形成的激基复合物发光的现象,激基复合物发光峰位于542nm左右。在激基复合物发光的影响下,器件的亮度和效率都不高。为了调制激基复合物发光的强度,用薄层的CBP作为隔离层加入到NPB和BDHFLYDFLQ材料之间。随着CBP厚度增加,激基复合物和电致激基复合物发光都被消除。当器件中CBP厚度为6nm时,器件中只有BDHFLYDFLQ激子发光,器件的外量子效率要明显高于有激基复合物发光的器件,同时器件的启亮电压也更低。     

新型高效红色磷光OLED器件

使用R-4B新型红色磷光染料作为掺杂剂,制作了结构为ITO/MoO3(10)/NPB(40)/TCTA(10)/CBP∶R-4B(x)/BCP(10)/Alq3(40)/LiF/Al的红色磷光器件,结合TCTA和BCP(电子和空穴阻挡材料),通过调节R-4B的掺杂比例,对器件的发光性能和发光机理进行了研究。结果表明,掺杂比例为6%时,得到光效和颜色稳定性较好的器件。在电压为4V时,电流密度为0.045mA/cm2,亮度为3.57cd/m2,最大电流效率为19.48cd/A;在电压分别为5、10和15V时,色坐标分别为(0.60,0.35)、(0.64,0.34)、(0.64,0.35)。分析认为,一方面,R-4B的发光机理主要有主体材料CBP对R-4B的能量传递及载流子直接注入R-4B形成激子;另一方面,TCTA和BCP的作用为对发光层内载流子、激子的阻挡及使空穴、电子更有效注入发光层。     

聚单乙氧基萘乙炔（PEONV）的电致发光特性

用可溶性前聚物法制备了单乙氧基取代的聚1．4萘乙炔（PEONV）。并采用PEONV作为有源层制作了单层结构电致发光器件。该器件的阳极为ITO，阴极为Ca，器件在正向偏压4V时开始发光，发光谱峰值605nm。最高亮度为156cd／m2。发光峰与未取代的PNV器件相比没有明显变化。文章对此作出了初步解释。     

Enhanced performance in organic light-emitting diodes by sputtering TiO2 ultra-thin film as the hole buffer layer

Organic light-emitting diodes were prepared using titanium oxide (TiO₂) ultra-thin film by RF magnetron sputtering as the hole buffer layer. The device configuration is ITO/TiO₂/N-N′-diphenyl-N-N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine/tris(8-quinolinolato)-aluminum/LiF/Al. The maximum luminous efficiency for the 1.2 nm TiO₂ device is increased by approximately 46% (6.0 cd/A), in comparison with that of the control device (4.1 cd/A). The atomic force microscopy shows that with the insertion of TiO₂ buffer layer, the roughness of ITO surface decreases, which is favorable to improve the device luminance and increase the device lifetime. The mechanism behind the enhanced performance is that the TiO₂ layer enhances most of the holes injected from the anode and improves the balance of the hole and electron injections.     

水溶胶CdSe纳米复合器件电致发光特性的研究

以巯基乙酸为稳定剂在水相中制备了水溶胶CdSe纳米晶,透射电子显微镜表明了纳米晶的形态和尺寸大小.用表面活性剂将CdSe纳米晶从水相中转移到有机相中,将其与具有空穴传输性能的聚合物PVK互溶在一起作为电致发光器件的发光层,以Alq3作为电子传输层,在发光层与Alq3之间加入了空穴阻挡层BCP制备了多层电致发光器件,研究了不同CdSe/PVK配比下水溶胶CdSe纳米复合器件的电致发光特性,结果发现随着水溶胶CdSe纳米晶在纳米复合物中所占比例的降低,电致发光器件的发光强度有所提高,起亮电压有所降低.     

Built-in voltage in organic light-emitting diodes with a use of Li2O/Al cathode

An effect of bilayer cathode Li2O/Al system was studied in Alq3 based organic light-emitting diodes with a variation of Li2O layer thickness from 0 to 10 nm. The device was made in a structure of ITO/(TPD)/Alq3/Li2O/Al. Current density-luminance-voltage (J-L-V) characteristics and a built-in voltage of the device were measured at ambient conditions. Built-in voltage in the device is generated due to a difference of work functions between the anode and cathode. From the J-L-V characteristics of the device, we observed an increase in luminance and current efficiency by more than 100 times and 2 times, respectively, for the device with 0.5 nm thick Li2O layer. The measured built-in voltage shows that the device with 0.5 nm thick Li2O layer has relatively higher built-in voltage compared to the others. Since the higher value of built-in voltage corresponds to the lower value of electron barrier height in cathode, the improvement in the efficiency for the device with 0.5 nm thick Li2O layer is thought to be due to a lowering of the electron barrier height.     

Application of ultra-thin CdS film as buffer layer in non-doped blue organic light-emitting diodes

The device inserted 0.5 nm thick cadmium sulfide (CdS) as buffer layer, prepared by vacuum thermal evaporation method, has been studied on the non-doped blue organic light-emitting diode. Compared to the device without ultra-thin CdS film, the maximum luminance of the device with ultra-thin CdS film was 11,370 cd/m² at 11 V, and the maximum current efficiency reached 3.10 cd/A, increased 1.5 times and 1.2 times, respectively. In the optimized devices with the structure of ITO/MoO₃ (10 nm)/TPABBI (35 nm)/Bphen (40 nm)/CdS (0, 0.1, 0.3 and 0.5 nm)/LiF (0.5 nm)/Al (100 nm), the effects of CdS layer on the photoelectric performance of the devices were investigated in detail. When the CdS thickness was 0.3 nm, the maximum luminance was 13,590 cd/m² at 9 V and the turn on voltage was only 3 V. The maximum current efficiency of 3.42 cd/A was obtained. It is indicated that the simple structure of the device with inserted ultra-thin CdS film, cheap and stable inorganic photoelectric material, may be a promising way to fabricate hybrid organic–inorganic LEDs with high performances.     

Organic light emitting devices with doped electron transport and hole blocking layers

This study reports on heterostructure OLEDs with n-type molecularly doped electron transport layer and hole blocking layer. The influence of doping on the operating voltage and on light emission performances was investigated. The n-type doping molecule is 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) dispersed into either an 8-(hydroquinoline) aluminum (Alq) electron transport layer (ETL) or a 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (Bathocuproine BCP) hole blocking layer (HBL). The typical device structure is glass substrate/indium tin oxide/PEDOT/TPD–F4-TCNQ/Alq–DCM/BCP/Alq/Mg–Ag where Poly(3,4)ethylenedioxythiophene/Polystyrenesulphonate (PEDOT/PSS) is a hole injecting layer, TPD–F4-TCNQ is a hole transport layer (HTL) made of N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) doped with 2 wt.% of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4-TCNQ) and Alq–DCM is the emitting layer (EML) made of Alq doped with 2 wt.% of 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) orange dye. The modified cathode consists in a combination of a BCP HBL and an Alq ETL where BCP or/and Alq were doped with PBD. Lowest operating voltage (3 V for a luminance of 10 Cd/m²) and brightest devices (6000 Cd/m²) were obtained with a hole blocking bilayer made of BCP doped with 28 wt.% deposited onto an undoped BCP (each one being 5 nm thick). Adding an undoped Alq layer improved the device current efficiency (4 Cd/A) but is detrimental to the operating voltage (6 V for a luminance of 10 Cd/m²). In the absence of real n-type doping with organic molecules, our results point out that the design of molecular doped injection layer at the cathode will need for a compromise between high luminance and efficiency on one hand and low operating voltage on the other hand.     

Modeling and numerical study of electrical characteristics of polymer light-emitting diodes containing an insulating buffer layer

In order to improve the electrical characteristic of polymer light-emitting diodes, a simple model for the device characteristic with an insulating buffer layer at cathode is proposed. This model is based on Fowleer-Nordhein tunneling mechanism and Poission's equation. An additional tunneling factor which characterises the tunneling effect of buffer layer is introduced. The simulated current-voltage characteristic indicates how an insulating buffer layer with suitable thickness decreases the barrier height at the cathode and therefore increases the electron injection. The model is validated by experimental results of devices with BaO as the buffer material and poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] as the emission material. An optimum thickness of the buffer layer is also obtained from the model, which provides a guide to device design.     

Study of buffer layer thickness on bulk heterojunction solar cell

We studied the effect of the buffer layer (molybdenum-oxide (MoO3)) thickness on the performance of organic solar cell based on blends of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester fullerene derivative (PCBM). The thickness of MoO3 was varied from 1 nm to 30 nm for optimization of device performance. The photocurrent-voltage and impedance spectroscopy were measured under dark and AM1.5G solar simulated illumination of 100 mW/cm2 for exploring the role of the buffer layer thickness on carrier collection at an anode. The MoO3 thickness of the optimized device (efficiency approximately 3.7%) was found to be in the range of 5 approximately 10 nm. The short-circuit current and the shunt resistance decrease gradually for thicker MoO3 layer over 5 nm. The device can be modeled as the combination of three RC parallel circuits (each one for the active layer, buffer layer and interface between the buffer layer and the active layer) in series with contact resistance (Rs approximately 60 ohm).     

Improved performance of the single-layer and double-layer organic light emitting diodes by nickel oxide coated indium tin oxide anode

The electrical and optical properties of the NiO films deposited under various conditions were first characterized. An ultra-thin layer of nickel oxide (NiO) was then deposited on the indium-tin oxide (ITO) anode to enhance the hole injection in the organic light-emitting diode (OLED) devices. A very low turn-on voltage (3 V) was actually observed for the device with the ITO/NiO anode in the conventional double layer heterojunction OLEDs. The enhancement of hole injection by the ITO/NiO anode was further verified by the hole-only device and by the device with a patterned NiO layer on the ITO anode. The luminance and the current density of the single-layer OLED device were also significantly improved by using the ITO/NiO anode to enhance the hole injection. Although the luminescence efficiency was low, the reasons of low efficiency were studied and the improvement method was proposed. Our results suggest that the NiO/ITO anode is an excellent choice to enhance the hole injection in OLED devices.     

铜酞菁缓冲层改善有机电致发光器件性能的机理研究

利用铜酞菁薄膜充当缓冲层，研究了缓冲层对有机电致发光器件性能的影响，研究结果表明含有铜钛菁缓冲层的器件性能时显优于不含有缓冲层的器件，加入铜酞菁冲层后器件发光稳定性也得到了改善。本文对相关机理进行了探讨，分析认为，铜酞菁本身的热稳定性和它能够降低空 穴注入势垒的性质是提高器件性能的主要原因。     

Electroluminescence and impedance analyses of organic light emitting diodes using anhydride materials as cathode interfacial layers

Pyromellitic dianhydride (PMDA) and trimellitic anhydride (TMA) were tried as cathode interfacial layers between tris-(8-hydroxyquinoline) aluminum (Alq₃) and Al in organic light emitting diodes (OLEDs). Both ultra-thin anhydride cathode interfacial layers improved the electroluminescence characteristics of OLEDs compared to those without any interfacial layer, and the PMDA interfacial layer showed the most significant enhancement of the device performance. According to impedance measurements and equivalent circuit analysis, the PMDA interfacial layer decreased the impedance, probably due to the increase in the injection efficiency of electrons from the Al cathode.