不同发光层基质材料的高效红色有机电致磷光器件

制备了以铱配合物(btp)2Ir(acac)磷光体为掺杂剂,分别以TPBi、 CBP 和Alq为发光层基质的红色电致磷光器件,比较了三种器件的性能.结果表明,在三种器件中,以Alq为基质的器件效率极低;以CBP为基质的器件,高的效率和好的色度相互矛盾;以TPBi为基质的器件性能最好,在驱动电流为4 mA/cm2时,色坐标为(x=0.62,y=0.35),亮度效率达2.43 cd /A.分析表明, (btp)2Ir(acac)分子在TPBi基质中的高效发光源于其对空穴的有效俘获.进一步的研究确定,(btp)2Ir(acac)分子在TPBi基质中的激子扩散长度为20 nm左右.     

微腔结构顶发射有机白光器件

结合微腔效应,通过调节不同发光层的厚度制作了顶发射有机白光器件.器件结构为Si/Ag/Ag2O/m-MTDATA/NPB/DPVBi/DCJTB:Alq3/Alq3/LiF/Al/Ag,其中DPVBi,DCJTB与Alq3的掺杂层分别作为蓝光和红光发光层,在选定490 nm的谐振波长时,通过调节DPVBi和掺杂层的厚度来实现对器件发光色度的调节.当DPVBi厚度为1 nm,电压为9 V时,器件的色坐标为(0.33,0.34),非常接近白光等能点.此项工作为利用微腔效应制作高效率高亮度顶发射白光器件奠定了基础.     

新型有机电致蓝色磷光器件的研究

研究了基于FIrpic的超薄非掺杂有机电致蓝色磷光器件的光电特性.改变超薄非掺杂FIrpic发光层以及其隔离层的厚度,可以调控FIrpic分子的聚集及激子相互作用强度对器件性能的影响.研究结果表明,具有TCTA 5 nm/FIrpic 1 nm/TCTA 5 nm/FIrpic 1 nm/TPBI 5 nm/FIrpic 1 nm多发光层结构的器件性能较优,最大发光效率为9.9 cd/A,超薄非掺杂发光层结构避免了掺杂方法中共沉积磷光材料浓度的精确控制,有利于简化器件制备工艺.     

空穴阻挡层对有机发光二极管寿命的影响

为研究空穴阻挡层对有机发光二极管寿命的影响,制备了含有空穴阻挡层的典型双层结构有机发光二极管,其中八羟基喹啉铝(Alq3)为发光层和电子传输层,BCP 为空穴阻挡层.器件的寿命随着发光层的厚度减小而降低,实验结果表明积累在发光层的空穴和激子可能是影响器件寿命的主要原因之一.     

红色OLED器件发光特性的研究

采用DCJTB作为红色染料，以绿色发光材料Alq，Gaq，Inq作主体材料。分别制备了结构为ITO／TPD／Mq(M=Al^3 ，Ga^3 ，In^3 )：DCJTB／Alq／LiF的一系列红色OLED器件，目的在于研究主体与客体发光分子间的能级匹配情况对载流子的注入、限制、激子的复合及发光色纯度方面的影响。同时研究了DCJTB的掺杂浓度，发光层中发光基质与掺杂染料之间的能带匹配，以及器件的各有机层之间的能带匹配对器件发光性能的影响。分析表明．在ITO／TPD／Alq(Gaq，Inq)：DCJTB／Alq／LiF／Al器件中．发光层中存在着从Mq向DCJTB的能量传递，Alq，Gaq，Inq与DCJTB之间的能带匹配显著地影响着这些器件的发光性能，如最大发光亮度、发光效率、色度-电压的关系等。     

Nb2O5空穴注入层的引入对OLEDs性能的影响

在有机发光二极管典型的层状结构中,引入磁控溅射制备Nb2O5超薄膜作空穴注入层,制备了结构为ITO/Nb2O5/TPD/Alq3/A1的器件.Nb2O5层的引入,降低了空穴注入势垒,增强了空穴注入,同时有效阻挡了ITo中ln向有机层的扩散,减少了发光猝灭中心的形成,提高了器件的亮度和效率.研究了不同厚度Nb2 O5层对器件光电性能的影响,发现:当引入Nb2O5层厚度为2 nm时,亮度提高了近2倍,效率由3.5 cd/A增加到了7.8 cd/A,较好地改善了器件的性能,并且性能优于含有CuPc常规注入层的器件.     

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.     

高效叠层有机电致发光器件

采用Cs2CO3:Alq3/MoO3作电荷产生层,制备出高效双单元串联型叠层有机发光器件.双单元叠层有机发光器件发光性能受电荷产生层MoO3的厚度影响很大.当MoO3厚度为30 nm时,叠层器件表现出最好的器件性能,最大电流效率达到14.5 cd/A.在相当宽的低电流密度范围内,30 nm MoO3叠层器件的电流效率是...     

具有新型电荷产生层的叠层有机发光器件

研究了采用薄层WO3作为叠层有机发光器件电荷产生层时的性能并对其厚度进行了优化,器件的电荷产生层由Li掺杂的电子注入层和高透明的WO3组成.研究表明,薄层WO3具有很高的透明度,并能有效地产生和注入空穴.叠层器件性能与单发光单元器件相比较,其亮度及效率均有大幅提高,叠层器件的最大电流效率达到了4.2 cd/A,在相同的电流密度下,叠层器件的效率约为传统器件的2倍;同时,电荷产生层的性能与WO3薄膜厚度密切相关,WO3薄膜厚度为3 nm时,器件的效率在整个电流范围内都保持稳定.采用薄层WO3作为电荷产生层为制备高效叠层有机发光器件提供了一条有效的途径.     

插入层TmP_yPb对白色有机电致发光二极管色纯度的影响

基于三原色白光器件ITO/NPB/TCTA/Ir(MDQ)2(acac)∶TCTA/TCTA/FIrpic∶TmPyPb/Ir(ppy)3∶TmPyPb/TmPyPb/LiF/Al,通过在其绿色与蓝色发光层之间插入不同厚度的TmPyPb,研究了该插入层的厚度对器件色纯度的影响。研究表明,插入层厚度的改变能够影响能量转移及调节激子的分布,当插入层厚度为4nm时,器件色坐标为(0.33,0.36),最大发光效率达11.58cd/A。     

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.     

Combinatorial Development of Blue OLEDs Based on Star Shaped Molecules

In this paper we describe the use of combinatorial vapor deposition techniques for the optimization of blue organic light emitting diodes (OLEDs). In these devices the star shaped molecule 1 with a triphenylamine core and three fluorene side groups serves as hole transport and emitting layer. Compound 2 with a much lower lying HOMO and a larger bandgap is used as hole blocking layer. Using combinatorial vapor deposition 42 OLEDs with thickness gradients of both the hole transport and the hole blocking layer have been simultaneously prepared on one substrate. The physical characterization of the devices clearly shows that a hole blocking layer of the star shaped molecule 2 is necessary in order to obtain pure blue emission with CIE coordinates of x = 0.15 and y = 0.15. A thickness of only 5 nm of the blocking layer is sufficient, and with increasing layer thickness the brightness of the blue devices drops. The blue devices exhibit a brightness of 400 cd m^–2 and a luminous efficiency of 2 cd A^–1. The thickness variations of both the hole transport and the hole blocking layer have been made in one combinatorial evaporation experiment on a single substrate using a set of movable masks. This demonstrates how efficient combinatorial methods can be used for the development of OLEDs.     

Detailed evaluation of in-operando potentials in OLED devices: A combined experimental and drift-diffusion study

We report on a technique to determine in-operando transport properties of Organic Light Emitting Diodes (OLEDs). Two types of OLEDs that solely differ in the emission layer but obviously exhibit a different potential distribution are investigated in this study. If the emission layer consists of the isomer TH-A a large shift in onset voltage can be observed in case of layer thickness variation of the emission layer. In case of the isomer TH-B a thickness variation has no impact on the onset voltage. Therefore the voltage developments per layer are determined with the help of IV measurements on a set of devices with varying layer thickness. From an empirical point of view the voltage behaviour in each layer follows a simple power law. A drift-diffusion model is developed that well describes the current density dependent evolution of coefficient and exponent of the power law. From the model we are able to derive the carrier injection mechanism into the respective layer as well as the injection barrier height. Also the carrier mobility is determined. Finally we are able to show that the existence of a large injection barrier can not explain the observed onset voltage shifts in case of TH-A. Instead an electric field at or close to the interface is necessary to describe the TH-A behaviour.     

利用PtOEP掺杂改善Spiro发光器件的发光效率

为了利用有机三线态发光提高有机发光器件的发光效率,用磷光材料掺杂到聚合物主体中作为发光层,制备有机电致发光器件.在测量器件的电流-电压特性、发光亮度-电压特性和电致发光谱的基础上,计算了器件的外量子效率,研究了磷光材料的掺杂浓度对器件发光效率的影响.结果表明,对特定的材料体系,适当控制掺杂浓度,可以同时观察到荧光和磷光光谱,使掺杂器件的外量子效率在纯聚合物发光器件的基础上得到明显提高.     

利用PtOEP掺杂改善Spiro发光器件的发光效率

为了利用有机三线态发光提高有机发光器件的发光效率,用磷光材料掺杂到聚合物主体中作为发光层,制备有机电致发光器件.在测量器件的电流-电压特性、发光亮度-电压特性和电致发光谱的基础上,计算了器件的外量子效率,研究了磷光材料的掺杂浓度对器件发光效率的影响.结果表明,对特定的材料体系,适当控制掺杂浓度,可以同时观察到荧光和磷光光谱,使掺杂器件的外量子效率在纯聚合物发光器件的基础上得到明显提高.     

Electromagnetic modeling of organic light-emitting devices

Based on the rigorous electromagnetic wave theory, a numerical model for simulating the radiation characteristics of organic light-emitting devices (OLEDs) is developed. In particular, a novel method for overcoming the numerical difficulty in taking the thick glass substrate into account is proposed. The numerical results confirm the importance of the effects of the thick glass substrate. The algorithms based on the numerical model are then used for evaluating the dependencies of OLED radiation characteristics on various parameters, including the thickness of different device layers and the cathode metal variety. In the study of the effect of emission layer (EML) thickness, it is found that the radiation spectral peak red shifts with increasing EML thickness. This trend is consistent with the experimental result.     

Enhance external quantum efficiency of organic light-emitting devices using thin transparent electrodes

High-index transparent electrodes have been one major origin of light trapping and lower light extraction in organic light emitting diodes (OLEDs). In this work, influences of the bottom transparent electrode thickness on emission properties of OLEDs are systematically studied by both simulation and experiments. Simulation shows that with substantially decreasing the thickness of the high-index indium tin oxide (ITO) electrode, waveguided modes, that otherwise would be significantly induced in regular/thicker ITO devices, can be effectively eliminated. Consequently, the overall coupling efficiencies of OLED emission into substrates can be much enhanced. Through further effective light extraction from the substrate, green phosphorescent OLEDs with a high external quantum efficiency (EQE) of up to ≈57.5% were experimentally demonstrated by adopting the very thin (20 nm) ITO electrode and preferentially horizontal dipole emitters (with a horizontal dipole ratio of 76%). The simulation further predicts that very high optical coupling efficiencies into substrates and EQEs approaching 80% are possible with further adopting purely horizontal dipole emitters and/or low-index electron transport layer (ETL) to suppress surface plasmon modes. Overall, this study clearly reveals the potential of using thin transparent electrodes for highly efficient OLEDs.     

Buffer-enhanced electron injection in organic light-emitting devices with copper cathode

We explore in this work the use of Cu as a cathode material in organic light-emitting devices (OLEDs) and find a dual electron–injection enhancement mechanism derived from the LiF layer. Different from what observed previously in Ag- and Au-cathode devices, the LiF buffer layer in the Cu-cathode OLEDs starts to play its role in performance improvement when it is much thinner than 3 nm, the optimal value of buffer thickness, and in the case of optimal thickness, the device exhibits excellent performance comparable to conventional Al-cathode device. The phenomenon observed is ascribed to enhanced electron injection as a result of combined effect of interfacial reaction and tunneling barrier reduction mechanism: while chemical reaction plays a key role at the very beginning of interface formation, tunneling dominates in the subsequent stage leading to the tremendous improvement of the characteristics.     

Organic light-emitting devices with a 2-(4-biphenyl)-5-(4-butylphenyl)-1,3,4-oxadiazole layer between the α-naphtylphenyliphenyl diamine and 8-hydroxyquinoline aluminum

Organic light-emitting devices (OLEDs) with a 2-(4-biphenyl)-5-(4-butylphenyl)-1,3,4-oxadiazole layer between the α-naphtylphenyliphenyl diamine and 8-hydroxyquinoline aluminum were fabricated using a vacuum evaporation method. Compared to the different thickness of the buffer layer, the OLEDs with the 1.0 nm buffer layer showed the maximum power efficiency. The enhancements in power efficiency result from an improved balance of hole and electron injections. After comparing among different density buffer layer, PBD are good candidates for hole-injecting buffer layer, and 1.0 nm PBD buffer layer shows better operational durability and life.