Dual enhancing properties of LiF with varying positions inside organic light-emitting devices

A multilayer organic light-emitting device (OLED) has been fabricated with a thin (0.3 nm) lithium fluoride (LiF) layer inserted inside an electron transport layer (ETL), aluminum tris(8-hydroxyquinoline) (Alq₃). The LiF electron injection layer (EIL) has not been used at an Al/Alq₃ interface in the device on purpose to observe properties of LiF. The electron injection-limited OLED with the LiF layer inside 50 nm Alq₃ at a one forth, a half or a three forth position assures two different enhancing properties of LiF. When the LiF layer is positioned closer to the Al cathode, the injection-limited OLED shows enhanced injection by Al interdiffusion. The Al interdiffusion at least up to 12.5 nm inside Alq₃ rules out the possible insulating buffer model in a small molecule bottom-emission (BE) OLED with a thin, less than one nanometer, electron injection layer (EIL). If the position is further away from the Al cathode, the Al diffusion reaches the LiF layer no longer and the device shows the electroluminescence (EL) enhancement without an enhanced injection. The suggested mechanism of LiF EL efficiency enhancer is that the thin LiF layer induces carrier trap sites and the trapped charges alters the distribution of the field inside the OLED and, consequently, gives a better recombination of the device. By substituting the Alq₃ ETL region with copper phthalocyanine (CuPc), all of the electron injection from the cathode of Al/CuPc interface, the induced recombination at the Alq₃ emitting layer (EML) by the LiF EL efficiency enhancer, and the operating voltage reduction from high conductive CuPc can be achieved. The enhanced property reaches 100 mA/cm² of current density and 1000 cd/m² of luminance at 5 V with its turn-on slightly larger than 2 V. The enhanced device is as good as our previously reported non-injection limited LiF EIL device [Yeonjin Yi, Seong Jun Kang, Kwanghee Cho, Jong Mo Koo, Kyul Han, Kyongjin Park, Myungkeun Noh, Chung Nam Whang, Kwangho Jeong, Appl. Phys. Lett. 86 (2005) 213502].     

Transparent flexible plastic substrates for organic light-emitting devices

In this paper, we describe the properties of flexible plastic substrates with a transparent conducting electrode (TCE), which are important for organic light-emitting devices (OLEDs). Specifically, we have evaluated the TCE electrical resistivity, surface roughness, electrode patterning, optical transmission, and the substrate water vapor/oxygen transmission. We have studied the effect of ultraviolet (UV)-ozone treatment on the TCE surface by using contact angle measurements and x-ray photoelectron spectroscopy (XPS). A decrease in the advancing contact angle by 30–40° and an increase of oxygen content on the TCE surface by 10 at.% were observed after the UV-ozone treatment. These changes facilitate the polymer adhesion to the TCE surface and increase the TCE surface work function, respectively. A sheet resistance of 12–13 Ω/□, an optical transmission greater than 80% over the visible range, and a surface roughness of 1.4–2.2-nm RMS over 50×50 μm² have been obtained for the plastic substrates. These properties are adequate for OLED applications based on United States Display Consortium specifications. Finally, we have found that a combination of hydrogenated amorphous silicon-nitride and silicon-oxide layers deposited on one side of the substrate at low-temperature reduces the water vapor and oxygen transmission rates (TRs) to less than 10⁻⁵ g/cm²-day-atm and about 10⁻⁷ cc/cm²-day-atm, respectively.     

Structure optimization of organic light-emitting devices

A triple layer organic light-emitting diode (OLED) with two heterostructure of indium-tin oxide (ITO)/N,N’-diphenyl-N, N’-bis(1-naphthyl) (1,1’-biphenyl)-4,4’-diamine (NPB)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/ 8-Hydrox- yquinoline aluminum (Alq3)/Mg:Ag has been fabricated by using the vacuum deposition method. The influence of different film thickness of BCP layer on the performance of the OLEDs has been investigated. The results show that when the thickness of the BCP layer film gradually r...     

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.     

一种新的多发光层白色有机电致发光器件

采用多发光层结构,将一种新型的黄橙色荧光染料2-溴-4-氟苯乙烯-8-羟基喹啉锌(BFHQZn,(E)-2-(2-bronw-4-fluorostyryl)quinolato-Zinc)与蓝色9,10-二-2-蔡蔥(ADN)组合在一起实现白光.研究了插入4,4-N,N-二咔唑联苯(CBP)对器件色度的影响,通过改变发光...     

有机电致发光器件的新型薄膜封装技术研究

针对有机电致发光器件(OLED)在空气中水汽和O2作用下寿命下降的问题,提出一种对OLED进行薄膜封装方法。封装薄膜由电子束蒸镀Al2O3薄膜和原子层沉积(ALD,atomic layer deposition)Al2O3薄膜相结合形成。利用Ca薄膜电学测试方法测定封装薄膜的水汽透过率(WVTR)。具体实现方法是,采用玻璃作为衬底,在100nm的Al电极上蒸镀200nm的Ca膜,然后对整个系统进行薄膜封装,只留出Al电极的一部分作为探针接触电极。实验发现,采用电子束蒸镀结合ALD的Al2O3薄膜封装,Ca薄膜变成透明的时间比未封装或采用单一结构封装得到了延长。为了检验薄膜封装效果,制作了一组绿光OLED,器件结构为ITO/MoOX(5nm)/mMTDATA(20nm)/NPB(30nm)/Alq3(50nm)/LiF(1nm)/Al,实验结果表明,本文提出的薄膜封装方法对器件进行封装,器件的寿命得到了延长。     

Solution-processable carbazole-based host materials for phosphorescent organic light-emitting devices

In this study, solution-processable carbazole-type host materials, 1,3-bis(3-(3,6-di-n-butylcarbazol-9-yl)phenyl)benzene (BCzPPh) and 4,6-bis(3-(3,6-di-n-butylcarbazol-9-yl)phenyl)pyrimidine (BCzPPm), were synthesized for use in phosphorescent organic light-emitting devices (OLEDs). Both host materials possess a high solubility in common organic solvents and high triplet energy to confine excitons to the phosphorescent emitter. The two nitrogen atoms in the central pyrimidine ring of BCzPPm have a profound effect on the photoluminescence properties and the electron-accepting capability. When doped with the green phosphorescent emitter tris(2-(4-tolyl)phenylpyridine)iridium (III), BCzPPh exhibited power efficiencies and external quantum efficiencies above 30 lm/W and 13%, respectively, in a simple bilayer OLED.     

高效率非掺杂型白色有机电致发光器件

制备了基于rubrene超薄层和NPBX做激子阻挡层的高效率的非掺杂型白色有机电致发光器件.器件结构为:ITO/2T-NATA(20 nm)/NPBX(25-d nm)/rubrene(0.2 nm)/NPBX(d nm)/DPVBi(30 nm)/Alq(30 nm)/LiF(0.5 nm)/Al.器件的电致发光光谱依靠激子阻挡层NPBX厚度d的变化而变化,当NPBX厚度d为5 nm时,器件色坐标从7 V变化到16 V时均在白光的中心区域,有最大电流效率7.91 cd/A(V=7 V)和最大亮度13 540 cd/m2 (V=16 V).     

有机/聚合物电致发光器件的稳定性问题

有机/聚合物电致发光(EL)器件走向实用化的最大障碍是其稳定性和寿命。文章综述了有机/聚合物EL器件的稳定性问题,并从器件的失效过程、电极材料及其界面对器件稳定性的影响及有机材料本身的稳定性等方面讨论了器件的稳定性。     

蓝光OLED的掺杂研究

采用蓝色发光材料ADN为主体发光材料、BAlq3为掺杂材料,通过改变BAlq3的掺杂浓度制备了结构为ITO/NPB/ADN:BAlq3/Alq3/Mg:Ag的一系列蓝光有机发光器件(OLED).研究了器件各有机层之间的能级匹配和BAlq3的掺杂浓度对载流子注入、传输、复合以及发光色纯度的影响.实验结果表明,空穴阻挡材料BAlq3的掺入显著影响OLED的电流密度、发光亮度、发光效率和发光光谱,当BAlq3的掺杂浓度为25%时,OLED的发光效率为1.0 lm/W,发光光谱的峰值为440 nm,色纯度为(0.18,0.15),未封装器件的半衰期为950小时,器件同时满足了高效率和高色纯度的要求.     

Research on flexible silver nanowire electrode for organic light-emitting devices

By spin-coating silver nanowires(AgNWs) and polymethyl methacrylate(PMMA), applying pressure imprint and plasma treatment, we obtained flat Ag NW thin film with a sheet resistance of 20 Ω/sq and a transmittance of 78% at 550 nm with low surface roughness. No significant change in sheet resistance was observed after cyclic bending(bending radius is 5 mm) test and tape test. After 1 000 bending tests, the change rate of sheet resistance was only 8.3%. The organic light-emitting devices(OLEDs) were prepared by using such Ag NW electrodes and a maximum brightness of 5 090 cd/m² was obtained. Compared with the Ag NWs electrode without any treatment, the present Ag NW electrodes have lower sheet resistance and better hole injection. Our results show spin-coated with flat layers, embossed and plasma-treated Ag NW electrodes are suitable for manufacturing flexible organic optoelectronic devices.     

Effective hole-injection layer for non-doped inverted top-emitting organic light-emitting devices

Non-doped inverted top-emitting organic light-emitting diode with high efficiency is demonstrated through employing an effective hole-injection layer composed of MoO_x. One reason for high efficiency lies on the energy-level matching between MoO_x and hole-transport, and another is due to the Ohmic contact formed between MoO_x and Ag. Both of them lead to an improvement of the hole-injection capability from Ag top anode. Moreover, the symmetrical current of “hole-only” device with MoO_x shows better hole-injection capability, which is independent of the deposition sequence. The optimized device with MoO_x hole-injection layer exhibits maximum current efficiency of 3.7 cd/A at a raised luminance level of 14,900 cd/m² and a maximum luminance of 47,000 cd/m² under 18 V.     

聚对二甲苯类薄膜用于有机电致发光器件的封装

采用热解化学气相沉积聚合(TCVDP)方法制备了聚对二甲苯(PPX)和聚一氯对二甲苯(PCPX)薄膜材料,利用其对有机电敛发光器件(OLED)进行了封装.利州紫外可见光谱、扫描电镜(SEM)对薄膜的相关性能进行了表征.比较了器件经过两种薄膜封装前后器件的工作寿命.实验结果表明:利用TCVDP方法,可以制备出透明的表面平整、结构致密的聚对二甲苯类薄膜材料;用于OLED)的封装能大幅度地提高器件的工作寿命,经过PPX封装后的寿命为1215 h,经过PCPX封装后的寿命为1 558 h,比未封装的器件寿命(197 h)提高了6～8倍.     

Improved efficiency of indium-tin-oxide-free flexible organic light-emitting devices

An indium-tin-oxide (ITO)-free flexible organic light-emitting device (OLED) with improved efficiency has been demonstrated by employing a template stripping process to create an ultrasmooth PEDOT: PSS anode on a photopolymer substrate. The device performance has been improved owing to lowered surface roughness of the PEDOT: PSS anode. A 38% enhancement in efficiency has been obtained. The ITO-free OLEDs on the polymer substrate have shown flexibility, and the device is free of cracks and dark spots under small bending radius. Moreover, the elimination of the H₂SO₄ residues on the surface of the H₂SO₄-treated PEDOT: PSS by the template stripping has demonstrated its beneficial effect on the device stability.     

Iminodibenzyl-substituted distyrylarylenes as dopants for blue and white organic light-emitting devices

A series of highly efficient blue materials based on iminodibenzyl-substituted distyrylarylene (IDB-series) fluorescent dyes using the concept of steric-compression have been designed and synthesized by means of a rigidized and over-sized ring. The steric-compression effect can shorten the effective conjugation length (chromophore) of the molecule and the added phenyl moiety in the core can alleviate the propensity for molecular aggregation. These materials also possess high glass transition temperature over 100 °C. The blue IDB-Ph device achieved a maximum external quantum efficiency of 4.8% with a Commission Internationale de l’Eclairage (CIE_x,y) coordinate of (0.16, 0.28). When applied in two-element white OLED system, the IDB-Ph doped device achieved a luminance efficiency of 11.0 cd/A with a CIE_x,y color coordinate of (0.29, 0.36).     

Low-temperature nickel-doped indium tin oxide anode for flexible organic light-emitting devices

Characteristics of an organic light-emitting diode (OLED) with a structure of Al/tris(8-hydroxyquinoline) aluminum (Alq3), N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1, 1′biphenyl-4, 4′-diamine(NPB)/indium tin oxide (ITO)/Arton film have been improved by the introduction of Ni atoms in the ITO surface layer. The threshold voltage and turn-on voltage of an OLED device with Ni sputter power of 90 W and ITO surface oxygen plasma treatment can be reduced, respectively, by 3.4 V and 2.6 V. The existence of Ni atoms and the formation of Ni oxide phases on ITO surface are suggested for the improved characteristics.     

基于CzHQZn发光的白光有机电致发光器件

利用一种新材料(E)-2-(2-(9-ethyl-9H-carbazol-3-yl)vinyl)quinolato-Zinc(CzHQZn)作空穴传输层和发光层制备了白光有机电致发光器件(WOLED),器件的结构为indium-tin oxide(ITO)/4,4′,4′′-{N,-(2-naphthyl)-N-phenylamino}-triphenylamine(2T-NATA)(22 nm)/CzHQZn(xnm)/N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine(NPBX)(ynm)/2,9-dimethyl,-4,7-diaphenyl,1,10-phenanthroline(BCP)(10nm)/tris(8-quinolinolato)aluminum(Alq3)(68-x-ynm)/LiF(0.5 nm)/Al。研究发现发光层CzHQZn和NPBX的厚度对器件的发光性能有较大的影响。当CzHQZn厚度x为22 nm、NPBX厚度y为8 mm时,得到了色度最好和效率最大的WOLED,最大电流效率为0.9 cd/A(at ...     

具有阶梯势垒的低压有机电致发光器件

在2-t-butyl-9,10-di-(2-naphthyl)anthracene(TBADN)/tris(8-hydroxyquinoline)aluminum(Alq3)界面及TBADN/4'7-diphyenyl-1,10-phenanthroline(Bphen)界面上插入Gaq薄膜作为阶梯势垒,使有机电致发光器件的电子注入得到改善.由于Gaq(2.9 eV)的LUMO(分子最低空余轨道能级)位于Alq3(3.1 eV)(或 Bphen(3.0 eV))的LUMO和TBADN的LUMO(2.8 eV)之间,形成了从Alq3(或Bphen)经Gaq到TBADN的势垒阶梯,提高了电子注入,进而提高了器件效率.实验表明:与没有阶梯势垒的器件相比,无论是单一电子器件还是完整器件,在相同电流密度下,具有阶梯势垒的器件的电压都有所下降.在电流密度为20 mA/cm2时,当电子传输层为Alq3时,单一电子器件的电压从7.9 V降到4.9 V,完整器件的电压从7 V降到5.8 V;当电子传输层为Bphen时,单一电子器件的电压从4.2 V降到3.1 V,完整器件的电压从6.2 V降到5.1 V.在电流密度为200 mA/cm2,Alq3为电子传输层时,亮度从1 992 cd/m2升到3 281 cd/m2,最高亮度达到3 420 cd/m2,Bphen为电子传输层时,亮度从1 745 cd/m2 升到2 876 cd/m2,最高亮度达到3 176 cd/m2.本文运用能级隧穿理论对上述现象进行了解释.     

Achieving full-color organic light-emitting devices forlightweight, flat-panel displays

We review recent results in the field of organic light-emitting devices (OLED's), with particular attention to the application of organic light-emitting devices to ultra-lightweight, full color, flat-panel displays. We show that OLED brightness, efficiency, operating voltage, and lifetime is sufficient to compete with other flat-panel display technologies such as backlit liquid crystal displays. We describe a novel, tunable OLED consisting of vertically stacked, transparent light-emitting devices which can serve as a color-tunable element in high-resolution full-color display., In addition, the unique physical properties of organic thin films allow for flexible, conformable, or foldable displays which are unobtainable with conventional, inorganic semiconductor technologies     

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.