Theoretical Investigation on the Electron and Energy Transfer between Peripheral Carrier Transport Groups and Central Chromophores in Electroluminescent Materials

The molecular materials with structures of luminescent core and peripheral carrier groups (e.g. carbazoles), have exhibited high‐performance in organic light‐emitting diodes (OLEDs). Present work is to understand the basic process of electronic and energy exchange between the peripheral functional groups and the central core through quantum chemical analysis. As an example, 4,7‐bis(9,9‐bis(6‐(9H‐carbazol‐9‐yl)hexyl)‐9H‐fluoren‐2‐yl)benzo[c]‐[1,2,5]thiadiazole (TCBzC) is investigated in regards to optoelectronic properties using density functional theory (DFT). The results suggest that the forbidden transition from peripheral carbazole to the central chromophore core makes for separated electrical and optical properties, and high performance electroluminescence (EL) is mainly attributed to the energy‐transfer from carbazoles to the fluorene derivative core     

Optically detected magnetic resonance studies of luminescence‐quenching processes in π‐conjugated materials and organic light‐emitting devices

It is widely recognized that nonradiative quenching of excitons by other excitons and polarons become the dominant decay mechanism of these excitons at high excitation densities. These quenching processes cause the roll‐off in the efficiency of organic light‐emitting devices (OLEDs) and prevent lasing at high injection current densities. This review presents the optically‐detected magnetic resonance (ODMR) evidence for these photoluminescence‐ and electroluminescence‐quenching processes. And while it provides such evidence for quenching of singlet excitons by polarons and triplet excitons, it reveals the central role of the strongly spin‐dependent annihilation of triplet excitons by polarons, since under normal excitation conditions the steady‐state polaron and triplet exciton populations are 100–10⁴ times the singlet exciton population. In addition, it also suggests that quenching of singlet excitons by bipolarons, likely stabilized by a counterpolaron or countercharge at specific sites, may also be a significant quenching mechanism that also affects the charge transport properties.     

TD-DFT investigation of electronic structures,photophysical properties and the theoretical design of OLEDs based on phosphorescent Ir(III) complexes bearing the non-π electron-conjugated carbene ligand

In the search for efficient phosphorescent materials, a rational design is presented for the iridium complex material (dfbmb)Ir(fptz)₂ (2) (dfbmb?=?1-(2,4-difluorobenzyl)-3-methylbenzimidazolium), which involves the use of two 2-pyridyl triazolate (fptz) chromophores and a non-π electron-conjugated high-field ligand dfbmb assembled by a saturated σ-bond methylene group, and a comparison with the benchmark (dfbmb)₂Ir(fptz) (1). In this work the electronic structures, absorption and phosphorescence spectra were investigated using the TD-DFT method. In order to obtain the mechanism of high phosphorescence yield in (1) and estimate the radiative rate constant k _r for (2), the radiative rate constant k _r, the spin-orbital coupling (SOC) matrix element, ΔE(S???T), and the square of the SOC matrix element (?ψ_S1|H_SO|ψ_T1?²) for (1) and (2) were measured. It is concluded that the switch of the cyclometalated ligand from the main chelate to the ancillary chelate seems to enhance the splitting of ΔE(S???T) in the current system. Finally, using the information gained, a PhOLED utilizing (1) and (2) was designed.     

Effect of a perfluorocyclopentene core unit on the structures and photoluminescence of fluorene- and anthracene-based compounds

A novel series of blue luminescent compounds, in which three identical functional groups, such as fluorene, anthracene, and spiro-bifluorene, are linked distortedly around a perfluorocyclopentene core, have been synthesized and characterized. The introduction of a perfluorocyclopentene linkage into the molecular framework leads to an enhancement of the photoluminescence (PL) efficiency and thermal stability. All compounds exhibit intense blue photoluminescence, which has been attributed to fluorene- or anthracene-based π→π* transitions. The maximum emission wavelengths of all compounds at room temperature are in the region of 420-480 nm, with higher PL quantum efficiencies than in 9,10-diphenylanthracene. The electroluminescent (EL) properties of compound 4, 1,2-bis(9,9′-spirobifluoren-2-yl)-3,3,4,4,5,5-hexafluorocyclopentene, were investigated. A multilayer EL device with the configuration of ITO/2TNATA(60 nm)/NPB(20 nm)/ADN:2%-compound-4(35 nm)/Alq₃(20 nm)/LiF(2 nm)/Al has been successfully fabricated.     

多层氧化物复合阴极透明OLED器件

制备了一种采用多层氧化物复合阴极的透明OLED,器件结构为:ITO/MoO3(10nm)/NPB(60nm)/Alq3(65nm)/Al(1nm)/MoO3(1nm)/Al(Xnm)/MoO3(30nm)。所采用的复合阴极结构为MoO3/Al/MoO3(MAM),同时在复合阴极(MAM)与电子传输层(Alq3)中间插入一层厚度为1nm的Al中间层,该薄Al层一方面提高了电极与有机层间界面的平整度,同时增强了电极的导电性;另一方面,在电子传输层与中间层Al薄膜之间形成了良好的欧姆接触,提高了电子的注入能力。改变MAM结构中Al的厚度,获得该透明OLEDs的最佳性能,在Al的厚度为18nm时器件亮度最高,为2 297cd/cm2。     

ITO的表面处理对有机电致发光器件性能的影响

作为有机电致发光器件(OLEDs)的一个主要部分,ITO的表面形貌以及表面性能对整个器件的性能起着决定性的作用。介绍了对ITO的各种处理方法,包括O2Plasma和UV ozone等。这些方法可以改变ITO的表面化学成分以及结构,可以大幅度地提高器件的亮度、寿命以及稳定性,使OLEDs的实用化成为可能。     

Electric‐Field‐Assisted Charge Generation and Separation Process in Transition Metal Oxide‐Based Interconnectors for Tandem Organic Light‐Emitting Diodes

The charge generation and separation process in transition metal oxide (TMO)‐based interconnectors for tandem organic light‐emitting diodes (OLEDs) is explored using data on electrical and spectral emission properties, interface energetics, and capacitance characteristics. The TMO‐based interconnector is composed of MoO₃ and cesium azide (CsN₃)‐doped 4,7‐diphenyl‐1,10‐phenanthroline (BPhen) layers, where CsN₃ is employed to replace the reactive metals as an n‐dopant due to its air stability and low deposition temperature. Experimental evidences identify that spontaneous electron transfer occurs in a vacuum‐deposited MoO₃ layer from various defect states to the conduction band via thermal diffusion. The external electric‐field induces the charge separation through tunneling of generated electrons and holes from MoO₃ into the neighboring CsN₃‐doped BPhen and hole‐transporting layers, respectively. Moreover, the impacts of constituent materials on the functional effectiveness of TMO‐based interconnectors and their influences on carrier recombination processes for light emission have also been addressed.     

Synthesis of polymer‐iridium complex and its electroluminescent characteristics

A π‐conjugated polymer‐iridium complex containing the ligand in the main chain was synthesized by the Suzuki coupling method, and was applied to organic light‐emitting devices (OLEDs) as the emitter material. The polymer‐iridium complex showed red photoluminescence and electroluminescence with the maximum external quantum efficiency of ca. 3% by using 4,4′‐N,N′‐dicarbazole‐biphenyl and 2‐(4‐biphenylyl)‐5‐(4‐tert‐butyl‐phenyl)‐1,3,4‐oxadiazole blended into the polymer emitter layer. Copyright © 2005 John Wiley & Sons, Ltd.     

Characterization of a passivation layer comprising MgO?SiO2 and ZrO2

Thin films with magnesium oxide (MgO) and silicon oxide (SiO₂) compounds mixed at various mixture ratios were deposited on flexible polyether sulfone (PES) substrates by an e‐beam evaporator to investigate their potential for transparent barrier applications. In this study, as the MgO fraction increased, thin films comprising MgO and SiO₂ compounds became more amorphous, and their surface morphologies became smoother and denser. In addition, zirconium oxide (ZrO₂) was added to the above‐mentioned compound mixtures, and the properties of the compound mixture comprising Mg? Si? Zr? O were then measured. ZrO₂ made the thin mixture films more amorphous, and made the surface morphology denser and more uniform. Whole thin films of 250 ± 30 nm in thickness were formed, and their water vapor transmission rates (WVTRs) decreased rapidly. The best WVTR was obtained by depositing thin films of Mg? Si? Zr? O compound among the whole thin films. The WVTRs of the PES substrate in the bare state decreased from 47 to 0.8 g m^?2 day^?1. This Mg? Si? Zr? O compound was deposited on polyethylene terephtalate (PET) substrates again to confirm the availability of the compound mixture. Thin films on the PET substrates decreased the WVTRs remarkably from 2.96 to 0.01 g m^?2 day^?1. These results were similar to those of thin films on PES substrates. As the thin mixture films became more amorphous and surface morphology denser and more uniform, the WVTRs decreased. Therefore, the thin mixture films became more suitable for flexible organic light emitting displays (OLEDs) as transparent passivation layers against moisture in air. Copyright © 2006 John Wiley & Sons, Ltd.     

含有Alq3和Znq2的可交联聚合物的合成与表征

合成了溶解性优良、带有可聚合链段的8-羟基喹啉金属螯合物(Alq3和Znq2)单体,在室温下通过紫外光照射,形成热力学性能稳定、8-羟基喹啉金属螯合物含量高(50(wt)%以上)的交联聚合物.这种材料可以解决使用旋涂的方法制备器件带来的底层溶解的问题,从而实现大面积、多层电致发光器件的制备,还可以通过光刻手段实现器件涂层图案化,是器件实现全彩色、超像素方法之一.其光致发光和电致发光性质证明这种材料本身以及其加工性能在有机/高分子平面显示技术领域有一定应用价值.