有机小分子电致磷光及发光机理研究进展

在过去10余年对小分子和聚合物电致发光器件的研究中,由于器件三线态激子能量没有得到充分的利用,使器件的内量子效率存在25%的理论极限,大大限制了其发光效率。为突破这一理论极限,在小分子主体材料中掺杂磷光染料制成电致磷光器件是近几年研究的热点,磷光染料的掺杂可以充分利用单线态和三线态激子,理论上器件的内量子效率可以达到100%。本文针对有机小分子电致磷光器件的发展、发光机理以及主客体分子间的能量传递等方面作了简明的讨论,指出了在器件设计时应该注意的一些问题。     

含卤素的纯有机小分子室温磷光材料研究概述

在最近几年中,纯有机小分子构建的室温磷光材料因其能够同时利用单线态激子和三线态激子,且相较于重金属掺杂体系和高分子体系,具有低毒性、制备简单等优点引起了人们极大的兴趣。通过介绍近几年含有卤素的有机小分子材料的室温磷光发光类型,讨论了室温磷光小分子在分子设计时需要综合考虑的各种因素。     

红色热激活延迟荧光材料的研究进展

通过反向系间窜越,热激活延迟荧光(TADF)材料可以同时利用三线态激子和单线态激子,使器件的理论内量子效率突破传统荧光材料的25%,达到理论上的100%,可与磷光材料相媲美,且材料价格便宜无需贵金属,因而受到人们广泛关注。近年来,对绿光及蓝光材料的研究进展较快,而红光材料由于分子结构的合理设计比较困难,研究进展相对较慢。从受体的类型出发,综述了近年来有关红色TADF材料的研究进展,并结合现有工作,对红色TADF材料的发展前景进行了展望。     

"光子-买一赠三”--简评有机三线态电致发光材料与器件进展*

有机电致发光材料与器件的研究已取得了重要进展,但要实现高信息含量的应用,器件的稳定性和效率仍须进一步提高。基于量子统计理论的研究结果表明,只有25%的电子空穴复合能量生成单线态激子,对于一个纯荧光的发光材料,在理论上,其器件效率的上限是光致发光效率的25%。三线态发光材料的应用,理论上可有效利用所有的复合能量,从而大幅度提高器件效率,目前已成为有机电致发光领域的研究热点。综述了有机三线态电致发光材料与器件的进展。     

新型含长链β-二酮环状金属铂配合物的光致发光和电致发光研究

测定了新型含长链β-二酮环状金属铂配合物YDETPt的量子效率、磷光寿命、吸收光谱和发光光谱,并研究了其光致发光和电致发光性能.结果表明,在521nm处有较强的金属配合物三重态磷光发射,是一种绿色磷光材料.配合物在主体材料中掺杂浓度为8%的器件,外量子效率最大,达到0.87%.     

一种新型红色磷光材料的合成及光物理性能研究

以2-甲基苯并噻唑、苯甲醛为原料,通过与三氯化铱配合,得到一种新型红色金属铱(Ⅲ) E-2-苯乙烯基苯并噻唑(SBT)乙酰丙酮(acac)配合物(SBT)2Ir(acac).通过质谱、核磁、红外光谱对其结构进行了表征,并对其光致发光性能进行了研究.研究结果表明:配合物(SBT)2 Ir(acac)在428和471nm处的紫外吸收属于单线态和三线态金属铱到配体的电荷转移吸收(1MLCT和3MLCT);在632nm处有强的金属配合物三线态磷光发射;(SBT)2Ir(acac)金属配合物的EHOMO=-4.8 eV,ELUMO=-2.5eV,磷光量子效率Φ (SBT)2Ir(acac) =0.19.(SBT)2Ir(acac)可能是一种极有潜力的电致磷光材料.     

热激活延迟荧光器件性能影响因素研究进展

热激活延迟荧光(TADF)材料能够充分利用单重态和三重态激子,其理论内量子效率可达100%,突破了传统荧光材料的极限。TADF材料具有生产成本低、易合成、效率高等优点,近年来受到了广泛关注。介绍了TADF材料分子设计和器件结构设计的基本原则,综述了近年来TADF器件的最新研究进展。     

有机电致发光器件掺杂研究进展

有机电致发光器件(Organic light-emitting device,OLED)因具有成本低、主动发光、驱动电压低、响应速度快、视角宽及可柔性显示等诸多优势,在平板显示及固态照明领域受到广泛关注。但无论是用作显示还是照明,色彩的应用都是不可或缺的。制备不同颜色的发光器件,除可以使用各种颜色的有机材料外,利用荧光或磷光染料掺杂也是重要的方法。同时,这种方法也可以大大提高器件的量子效率。尤其从理论上来说,磷光OLED的内量子效率可以达到100%。从OLED的掺杂原理、荧光掺杂与磷光掺杂等方面阐述了OLED的研究进展。     

有机半导体照明(有机照明)研究进展

采用有机发光二极管(OLEDs)的有机半导体照明(有机照明)是绿色环保、健康安全的新型面光源,有望在固态照明领域得到广泛的应用。有机照明的发展是随着有机发光材料的不断进步而进步的。有机发光材料从最初的荧光材料发展到磷光材料以及最近提出的热活化延迟荧光材料,其性能在不断地提升。基于这些材料的白光OLEDs的性能也在不断提升。最早的白光器件基于荧光小分子材料,但是由于只能利用单线态激子发光,效率很低。随后磷光材料的引入使得白光器件的效率大幅度提升,但是由于蓝色磷光材料本身的稳定性问题,全磷光白光器件的寿命较短。为了结合荧光和磷光的优点,人们提出了荧光/磷光杂化的白光器件,这是目前最有前景的一类白光器件结构。目前针对有机照明的研究,已从早期只关注效率突破阶段,进入到综合提高效率和寿命阶段。从荧光白光、磷光白光以及荧光/磷光混合白光3个方面对有机照明的研究状况、发展趋势进行了介绍。     

一种新型金属铱(Ⅲ)类磷光材料的合成及性能研究

以邻氨基苯硫酚、苯甲酰氯为起始原料,通过与三氯化铱配合反应,合成了一种新型金属铱的(2-苯基苯并噻唑)配合物(bt)2Ir(acac),产率为45.47%,熔点为303～304℃.通过质谱、元素分析及红外光谱对其结构进行了表征,并对其光致发光性质进行了研究.研究表明,配合物在350～450nm存在单线态和三线态金属铱到配体的电荷跃迁,在566.0 nm处有强的金属配合物三线态磷光发射,配合物(bt)2Ir(acac)是一种新型的磷光材料.     

Recent progresses on materials for electrophosphorescent organic light-emitting devices

Although organic light-emitting devices have been commercialized as flat panel displays since 1997, only singlet excitons were emitted. Full use of singlet and triplet excitons, electrophosphorescence, has attracted increasing attentions after the premier work made by Forrest, Thompson, and co-workers. In fact, red electrophosphorescent dye has already been used in sub-display of commercial mobile phones since 2003. Highly efficient green phosphorescent dye is now undergoing of commercialization. Very recently, blue phosphorescence approaching the theoretical efficiency has also been achieved, which may overcome the final obstacle against the commercialization of full color display and white light sources from phosphorescent materials. Combining light out-coupling structures with highly efficient phosphors (shown in the table-of-contents image), white emission with an efficiency matching that of fluorescent tubes (90 lm/W) has now been realized. It is possible to tune the color to the true white region by changing to a deep blue emitter and corresponding wide gap host and transporting material for the blue phosphor. In this article, recent progresses in red, green, blue, and white electrophosphorescent materials for OLEDs are reviewed, with special emphasis on blue electrophosphorescent materials.     

新型有机电致荧光材料研究进展

有机发光二极管因独特的优势被看作新一代的照明及平面显示技术,引起了研究人员的广泛关注。传统的荧光材料仅能利用单重态激子发光,因而效率并不理想。近年来,能够利用三重态激子能量发光的新型荧光材料的研究实现了新的突破。按照三重态激子到单重态激子的转化机理,荧光材料可以分为三重态-三重态湮灭、热致延迟荧光和局域电荷转移杂化激发态三种特殊类型。本文围绕着这几种类型的荧光材料展开了探讨,介绍了有机电致荧光器件的概况以及不同类型荧光材料的发光机理,并从分子设计的角度说明了高性能发光器件的设计思路。     

Photoluminescence Quenching Probes Spin Conversion and Exciton Dynamics in Thermally Activated Delayed Fluorescence Materials

Fluorescent materials that efficiently convert triplet excitons into singlets through reverse intersystem crossing (RISC) rival the efficiencies of phosphorescent state‐of‐the‐art organic light‐emitting diodes. This upconversion process, a phenomenon known as thermally activated delayed fluorescence (TADF), is dictated by the rate of RISC, a material‐dependent property that is challenging to determine experimentally. In this work, a new analytical model is developed which unambiguously determines the magnitude of RISC, as well as several other important photophysical parameters such as exciton diffusion coefficients and lengths, all from straightforward time‐resolved photoluminescence measurements. From a detailed investigation of five TADF materials, important structure–property relationships are derived and a brominated derivative of 2,4,5,6‐tetrakis(carbazol‐9‐yl)isophthalonitrile that has an exciton diffusion length of over 40 nm and whose excitons interconvert between the singlet and triplet states ≈36 times during one lifetime is identified.     

Organic Materials for Deep Blue Phosphorescent Organic Light‐Emitting Diodes

Recently, great progress has been made in the device performance of deep blue phosphorescent organic light‐emitting diodes (PHOLEDs) by developing high triplet energy charge‐transport materials, high triplet energy host and deep blue emitting phosphorescent dopant materials. A high quantum efficiency of over 25% and a high power efficiency of over 15 lm/W have already been achieved at 1000 cd m^?2 in the deep blue PHOLEDs with a y color coordinate less than 0.20. In this work, recent developments in organic materials for high efficiency deep blue PHOLEDs are reviewed and a future strategy for the development of high efficiency deep blue PHOLEDs is proposed.     

New Trends in the Use of Transition Metal–Ligand Complexes for Applications in Electroluminescent Devices

The advantage of using phosphorescent transition metal–ligand complexes in optoelectronic applications such as organic light‐emitting diodes (OLEDs) and light‐emitting electrochemical cells (LECs) are described and evaluated. Additionally, different device constructions utilizing phosphorescent transition‐metal complexes like iridium(III ) mixed‐ligand complexes and ruthenium(II ) systems are reviewed and specified. Diverse host materials in which the phosphorescent emitters can be placed are discussed, such as small organic molecules and a few polymeric systems, and alternative processing technologies are briefly compared. Recent developments in the synthesis of iridium(III ) triplet emitters are discussed. Different device architectures require different kinds of metal–ligand complexes. The different synthetic routes leading to charged and non‐charged complexes are briefly discussed.     

Highly efficient blue- and white-organic light-emitting diode based on dual recombination zones with a charge control layer

Highly efficient blue phosphorescent organic light-emitting diodes are investigated using iridium(Ill) bis[(4,6-di-fluorophenyl)-pyridinato-N,C2']picolinate doped in N,N'-dicarbazolyl-3,5-benzene (mCP) with a charge control layer (CCL) as the dual recombination zone (DRZ) system. DRZ with CCL was used to form a broad recombination zone and exciton confinement within each emission zone. Holes and electrons can be easily transported through the CCL, which were a mixed p-type mCP and n-type 2,2',2"-(1,3,5-benzenetryl) tris(1-phenyl)-1H-benzimidazol, for controlling the carrier movement. The CCL can play a role in triplet exciton blocking as expected from high triplet energy levels as well. Additionally, a white organic light-emitting diode was fabricated using a new phosphorescent orange emitter: bis[2-(2,4-difluorophenyl)pyridinato]iridium 2-(2-hydroxyphenyl)benzothia zolate doped in DRZ. The white device showed a maximum luminous efficiency of 23.15 cd/A, a maximum external quantum efficiency of 9.56%, and a maximum power efficiency of 13.37 lm/W. It also showed white emission with CIEx,y coordinates of (x = 0.33, y = 0.41) at 8 V.     

Long-range resonantly enhanced triplet formation in luminescent polymers doped with iridium complexes

The current drive to produce cheap, flexible plastic displays has led to rapid improvements in device efficiency. Inclusion of highly phosphorescent heavy-metal organic complexes as dopants ensures that both singlet and triplet excitations formed on charge recombination can be used efficiently to emit light. However, the inclusion of these dopants affects the photophysics of the host in a surprising way, generating a ten- to twenty- fold instantaneous increase in the number of host triplet states, independent of host triplet energy, quenching up to 95% of all singlet states. Once created however, these triplets are only weakly quenched by the same mechanism. We ascribe this to a resonant, remote intermolecular heavy-atom effect that greatly increases the inter-system crossing rate of the host polymer arising through the strong overlap of the delocalized pi orbitals of the host and ligands. This mechanism competes effectively with F?rster energy transfer, and operates over large distances.     

Small Molecule Host Materials for Solution Processed Phosphorescent Organic Light‐Emitting Diodes

Solution processed phosphorescent organic light‐emitting diodes (OLEDs) have been actively developed due to merits of high quantum efficiency of phosphorescent materials and simple fabrication processes of solution processed OLEDs. The device performances of the solution processed phosphorescent OLEDs have been greatly improved in the last 10 years and the progress of the device performances was made by the development of small molecule host materials for solution processes. A hybrid host of polymer and small molecules, a single small molecule host and a mixed host of small molecule hosts have effectively enhanced the quantum efficiency of the solution processed phosphorescent OLEDs. Therefore, this paper reviews recent developments in small molecule host materials for solution processed phosphorescent OLEDs and provides future directions for the development of the small molecule host materials.