π-Extended Carbazole Derivatives as Host Materials for Highly Efficient and Long-Life Green Phosphorescent Organic Light-Emitting Diodes

High-performance organic light-emitting diodes (OLEDs) that use phosphorescent and/or thermally activated delayed fluorescence emitters are capable of realizing 100 % electron-to-photon conversion. The host materials in these OLEDs play crucial roles in determining OLED performance. Carbazole derivatives are frequently used as host materials, among which 3,3-bis(9H-carbazol-9-yl)biphenyl ( mCBP ) is often used for lifetime testing in scientific studies. In this study, the π conjugation of the carbazole unit was expanded to enhance OLED lifetime by designing and developing two benzothienocarbazole (BTCz)-based host materials, namely m1BTCBP and m4BTCBP . Among these host materials, m1BTCBP formed a highly efficient [Ir(ppy)₃]-based OLED with an operational luminescence half-life (LT₅₀) of over 300 h at an initial luminance of approximately 12000 cd m⁻² (current density: 25 mA cm⁻²). The LT₅₀ value at 1000 cd cm⁻² was estimated to be about 23 000 h. This performance is clearly higher than that of mCBP -based OLEDs (LT₅₀≈8500 h).     

Dibenzo[a,j]phenazine‐Cored Donor–Acceptor–Donor Compounds as Green‐to‐Red/NIR Thermally Activated Delayed Fluorescence Organic Light Emitters

A new family of thermally activated delayed fluorescence (TADF) emitters based on U‐shaped D‐A‐D architecture with a novel accepting unit has been developed. All investigated compounds have small singlet‐triplet energy splitting (ΔE_ST) ranging from 0.02 to 0.20 eV and showed efficient TADF properties. The lowest triplet state of the acceptor unit plays the key role in the TADF mechanism. OLEDs fabricated with these TADF emitters achieved excellent efficiencies up to 16 % external quantum efficiency (EQE).     

掺杂发光有机电致磷光器件工作原理及主体材料

本文总结了基于掺杂发光的有机电致磷光器件(PhOLED)中磷光材料被激发的途径及机理,并指出不同主体材料对器件性能的不同影响.全面介绍了小分子主体材料研究的新进展及它们在PhOLEDs器件中的运用.比较和讨论了基于各种不同性质主体材料的器件性能,指出主体材料选择策略.同时讨论了各类主体材料的分子结构、热稳定性、三线态能级、载流子迁移率及HOMO/LUMO能级之间的关系,揭示了上述特性对器件性能影响.     

Effective Host Materials for Blue/White Organic Light‐Emitting Diodes by Utilizing the Twisted Conjugation Structure in 10‐Phenyl‐9,10‐Dihydroacridine Block

Two new 10‐phenyl‐9,10‐dihydroacridine derivatives attached by dibenzothiophene (DBT) and dibenzofuran (DBF) were synthesized. The influence of the substituents of these materials was studied by theoretical calculations (DFT calculation) and experimental measurements. Owing to the twisted N‐phenyl ring, both molecules possess sufficiently high triplet energies and are suitable as hosts for phosphorescent organic light‐emitting diodes. To evaluate the electroluminescent (EL) performance of these materials, FIrpic‐based blue PHOLEDs and two‐color white PHOLEDs (FIrpic and PO‐01 as the dopants) were fabricated using the common device structures. High external quantum efficiencies (EQE) of 21.1 % and 20.9 % for FIrpic‐based blue PHOLEDs were achieved by FPhAc and TPhAc, respectively. The white device based on the host FPhAc achieved a higher performance, with a maximum EQE of 24.7 % than the device with TPhAc as host material.     

Recombination radiation from organic solids

The recombination radiation from organic solids, defined as the light emission following the fusion of oppositely charged carriers into an electrically neutral state, is discussed as a phenomenon underlying the function of organic light-emitting diodes (LEDs). Its intensity and spectral range depend on the population and nature of the emissive states, which differ, in general, from those created using light. These differences are pointed out and shown to be a result of the reverse pathways of the mutual transformation of localized molecular excitons and coulombically-correlated charge-pair excited states formed either by photoexcitation or electron-hole recombination. Spectral features of the radiation produced by the recombination of statistically independent charge carriers are discussed in terms of two molecules-based excited states like excimers or electromers in single-component materials and exciplexes or electroplexes in multicomponent materials. Consequences for optical and electrical characteristics of organic LEDs are discussed and illustrated by examples. Progress in the fundamental and applied research may be expected based on properties of recombination-produced electronic excited states.     

Phosphine oxide-functionalized polyfluorene derivatives:Synthesis,photophysics,electrochemical properties,and electroluminescence performance

A series of phosphine oxide-functionalized polyfluorene derivatives,PFH-PO-40-1 (P1),PFH-PO-20-1 (P2),PFH-PO-10-1 (P3),and PFH-PO-1-1 (P4),were prepared via a palladium-mediated Suzuki cross-coupling reaction.The structures and purities of all polymers were fully characterized by 1H and 13C NMR,UV-vis and photoluminescent spectroscopy,gel permeation chromatography,and TGA/DSC.Their emission features showed single broad peaks at about 445 nm in film,compared with those in dilute solutions,which might be caus...     

无间隔层结构的高效率荧光/磷光混合型白光有机发光二极管

采用磷光红光/荧光蓝光/磷光绿光无间隔层三发光层结构,制备出了高效率荧光/磷光混合型白光有机发光二极管(OLEDs),其中选取具有高荧光量子产率(PLQY)的荧光染料4P-NPD(双[N-(1-萘基)-N-苯基-氨基]四联苯)作为蓝光发射分子,以及常用的高效磷光染料Ir(MDQ)₂(acac)和Ir(ppy)₃(acac)分别作为红光和绿光的客体,通过混合和掺杂的方法制备了相应的发光层,实现了发光层中激子的有效利用和白光发射。 制备的白光器件最大电流效率和功率效率分别达到了27.1 cd/A和30.3 lm/W,当电压为6 V时,CIE色坐标为(0.33,0.41),显色指数CRI为70,色温CCT为5432 K。 在此基础上,设计制备了高色温的荧光/磷光混合型白光OLEDs,其色温(CCT)达到了7106 K。     

9,9′-Bicarbazole: New Molecular Skeleton for Organic Light-Emitting Diodes

Carbazole is a classic tricyclic aromatic compound that has been widely used in organic optoelectronics. Appropriate functionalization on its aromatic rings will significantly increase the possibilities for its application as an optoelectronic material. Position engineering of carbazole not only leads to its structural diversity, but also substantially enriches its functionality. Bicarbazoles have 15 isomers, most of which are well studied and have been applied in organic light-emitting diodes (OLEDs). However, one isomer, 9,9′-bicarbazole, is rarely investigated as an OLED material. Therefore, two 9,9′-bicarbazole derivatives, 3,3′-di(10H-phenoxazin-10-yl)-9,9′-bicarbazole and 3,3′-di(10H-phenothiazin-10-yl)-9,9′-bicarbazole, have been designed and prepared for use as host materials for green and red OLEDs. These two compounds demonstrated good device performances, and it is believed that the 9,9′-bicarbazole building block could be a novel platform for the design of efficient host materials for OLEDs.     

位阻型有机电致磷光材料的研究进展

重金属旋轨耦合作用使磷光有机发光二极管的内量子效率在理论上可达100%,突破了传统有机荧光二极管内量子效率为25%的限制,是目前最有潜力的第三代显示器.但是,磷光材料常因浓度猝灭、三线态湮灭、二聚体发光等因素影响器件性能.位阻型磷光材料能够抑制分子间的强相互作用,从而解决了上述问题.本文作者综述了近年来具有大体积空间位阻效应的铱(III)、铂(II)、锇(II)等有机小分子磷光材料的研究进展,讨论了其目前存在的问题和未来的发展趋势.     

带烷氧基的苯基蒎烯吡啶铱配合物在聚合物电致发光器件中的应用研究

采用旋涂法将一组带烷氧基的苯基蒎烯吡啶铱(Ⅲ)配合物(Ir(RO-pppy)₃)磷光材料掺杂到PVK中,制作出了聚合物电致发光器件:ITO/PE-DOT:PSS(40 nm)/PVK_0.7:PBD_0.3:(x%.)Ir-complex(80 nm)/CsF(1.5 nm)/Mg:Ag(200 nm).实验结果表明,带有长烷氧基链配体的铱(Ⅲ)配合物能表现出更好的器件行为,当掺杂浓度为3.2%时,器件的最高发光效率达19.9 cd/A(7.8 lm/W,9.1V),CIE为(0.20,0.56);器件最大亮度为15700 cd/m²(8.4V).通过对这组铱(Ⅲ)配合物的光物理行为及电化学性能的研究,考察了主体材料与配合物之间的能级配置以及能量转移的机理.     

Selective Introduction of Carbazole and Diphenylamine into Spirofluorenexanthene Core for Different Phosphorescent Hosts

Built on the spiro[fluorene‐9,9′‐xanthene] (SFX) core and two frequently‐used hole‐transporting groups such as carbazole and diphenylamine, two SFX derivatives, namely SFXCz and SFXDPA, have been synthesized by one‐step reaction for red, green and blue phosphorescent organic light‐emitting devices (PHOLEDs). Though the properties of these two groups are very similar, the devices based on SFXCz and SFXDPA exhibit distinct performances. In blue PHOLEDs, the device based on SFXCz exhibited much better performances than that based on SFXDPA. However, the latter was superior to the former in green and red PHOLEDs. And the red PHOLED based on SFXDPA exhibited maximum current efficiency (CE) of 27.1 cd·A^?1, power efficiency (PE) of 25.0 lm·W^?1, and external quantum efficiency (EQE) of 15.0%. The results show that the introduction of diphenylamine group is suitable for constructing green and red host materials, whereas the introduction of carbazole group is suitable for constructing blue host materials.     

基于咔唑-三唑的新型主体材料及天蓝光有机电致磷光器件

本研究针对蓝光主体材料相对缺乏的现状,利用有机电致磷光器件高效率的优势,选择1,2,4-三唑为电子传输功能基团、咔唑为空穴传输功能基团,设计、制备了新型主体材料oCzTz。通过邻位取代方式实现了分子立体构型高度扭曲,从而使分子的三重态能量达到3.01eV;oCzTz具有较高的热分解温度(353℃)和玻璃化转变温度(110℃);量化计算显示,分子的前线轨道在咔唑和三唑基团之间高度分离。以oCzTz为主体、以FIrpic为发光客体的天蓝光电致磷光器件启亮电压为3.4V,电流效率和功率效率分别高达37.2cd·A-1和29.2lm·W-1,是以TPBI为电子传输层的同类器件的最高效率之一。     

Hole‐transporting host‐polymer series consisting of triphenylamine basic structures for phosphorescent polymer light‐emitting diodes

A series of novel styrene derived monomers with triphenylamine‐based units, and their polymers have been synthesized and compared with the well‐known structure of polymer of N,N′‐bis(3‐methylphenyl)‐N,N′‐diphenylbenzidine with respect to their hole‐transporting behavior in phosphorescent polymer light‐emitting diodes (PLEDs). A vinyltriphenylamine structure was selected as a basic unit, functionalized at the para positions with the following side groups: diphenylamine, 3‐methylphenyl‐aniline, 1‐ and 2‐naphthylamine, carbazole, and phenothiazine. The polymers are used in PLEDs as host polymers for blend systems with the following device configuration: glass/indium–tin–oxide/PEDOT:PSS/polymer‐blend/CsF/Ca/Ag. In addition to the hole‐transporting host polymer, the polymer blend includes a phosphorescent dopant [Ir(Me‐ppy)₃] and an electron‐transporting molecule (2‐(4‐biphenyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole). We demonstrate that two polymers are excellent hole‐transporting matrix materials for these blend systems because of their good overall electroluminescent performances and their comparatively high glass transition temperatures. For the carbazole‐substituted polymer (T_g = 246 °C), a luminous efficiency of 35 cd A^?1 and a brightness of 6700 cd m^?2 at 10 V is accessible. The phenothiazine‐functionalized polymer (T_g = 220 °C) shows nearly the same outstanding PLED behavior. Hence, both these polymers outperform the well‐known polymer of N,N′‐bis(3‐methylphenyl)‐N,N′‐diphenylbenzidine, showing only a luminous efficiency of 7.9 cd A^?1 and a brightness of 2500 cd m^?2 (10 V). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3417–3430, 2010     

基于氟代苯并咪唑配体的绿光铱配合物的合成与表征

基于一种氟代的配体2-(4’-氟苯基)-1-苯基-苯并咪唑,在高温(>200℃)条件下直接合成了经式绿光铱配合物mer-Ir(FPBI)3,并通过1H NMR和单晶X射线衍射分析确定了其经式构型。不同于以前报道的具有经式构型的铱配合物(<0.1),mer-Ir(FPBI)3在甲苯溶液中的光致发光量子效率高达0.46。应用该配合物制备了高效磷光有机电致发光器件,最大电流效率和外量子效率分别为38.5 cd/A和11.8%,色坐标为(0.29,0.58)。     

红色铱配合物磷光材料及器件的研究进展

有机电致发光器件具有驱动电压低、高亮度、高效率等优点,引起了研究人员的广泛关注,在固态照明和平板显示领域具有广阔应用前景。 在绿、蓝、红三基色器件中,绿光器件和蓝光器件的性能普遍优于红光器件,基本满足了产业化的需要;目前红色有机电致发光材料及器件的研究进展相对缓慢。 因为红光材料的能隙较窄,致使主客体材料之间能级匹配困难,导致红光器件普遍效率低、色纯度差,但是,红光材料是获得白光器件必不可少的材料。 因此,如何获得高性能红光材料对于有机电致发光器件的发展至关重要。 本文综述了近年来红色铱配合物磷光材料及器件的研究进展,对提升效率和色纯度的方法进行重点阐述;并结合现有工作,对红色有机电致磷光材料与器件的前景进行展望。     

Organic electroluminescent devices containing phosphorescent molecules in molecularly doped hole transporting layer

We demonstrate high-efficient simple electrophosphorescent devices comprised of tris{4-[N-(3-methylphenyl)anilino]phenyl}amine (m-MTDATA) dispersed in a polycarbonate (PC) matrix as a hole-transporting layer (HTL), and 2-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as an electron-transporting layer (ETL). The HTL doped with a complex phosphor fac-tris(2-phenylpyridine)iridium, [Ir(ppy)₃], and/or 5,6,11,12-tetraphenyltetracene (rubrene) fluorescent dye is shown to act as an emitter. Devices containing [Ir(ppy)₃] as a single HTL dopant show the highest external quantum efficiency (QE) reaching 9 % (photon/electron) due to direct electron-hole recombination on phosphorescent [Ir(ppy)₃]. A decrease in QE of one order of magnitude at high current densities is observed in all devices. Addition of rubrene to [Ir(ppy)₃]-doped devices shifts the maximum QE towards larger current densities.     

Deep-Red and Near-Infrared Iridium Complexes with Fine-Tuned Emission Colors by Adjusting Trifluoromethyl Substitution on Cyclometalated Ligands Combined with Matched Ancillary Ligands for Highly Efficient Phosphorescent Organic Light-Emitting Diodes

Six novel Ir(C^N)₂(L^X)-type heteroleptic iridium complexes with deep-red and near-infrared region (NIR)-emitting coverage were constructed through the cross matching of various cyclometalating (C^N) and ancillary (LX) ligands. Here, three novel C^N ligands were designed by introducing the electron-withdrawing group CF₃ on the ortho (o-), meta (m-), and para (p-) positions of the phenyl ring in the 1-phenylisoquinoline (piq) group, which were combined with two electron-rich LX ligands (dipba and dipg), respectively, leading to subsequent iridium complexes with gradually changing emission colors from deep red (≈660 nm) to NIR (≈700 nm). Moreover, a series of phosphorescent organic light-emitting diodes (PhOLEDs) were fabricated by employing these phosphors as dopant emitters with two doping concentrations, 5% and 10%, respectively. They exhibited efficient electroluminescence (EL) with significantly high EQE values: >15.0% for deep red light0 (λ_max = 664 nm) and >4.0% for NIR cases (λ_max = 704 nm) at a high luminance level of 100 cd m⁻². This work not only provides a promising approach for finely tuning the emission color of red phosphors via the easily accessible molecular design strategy, but also enables the establishment of an effective method for enriching phosphorescent-emitting molecules for practical applications, especially in the deep-red and near-infrared region (NIR).     

一类以菲衍生物为配体的新型红色到近红外磷光配合物的合成及其光致和电致发光性质

以2-(菲-9)-吡啶、1-(菲-9)异喹啉和喹喔啉并[2,3-l]菲为配体,合成了3个新颖的红色到近红外磷光配合物(pypt)2Ir(acac)、(sqpt)2Ir(acac)和(qupt)2Ir(acac).对这些配合物的吸收、发射光谱和电化学性质进行了研究,结果发现,菲取代基的性质主要影响配合物的LUMO能级,随着菲取代基共轭程度的增加,吸收光谱和发射光谱红移,光致发光(PL)光谱从619 nm红移到704 nm.将4%的(sqpt)2Ir(acac)掺杂在PVK+PBD主体材料中制备了掺杂磷光发光器件,器件电致发光(EL)光谱的λmax为704 nm,器件的EL光谱从红色一直延伸到近红外区域.