Phosphorescent organic light emitting diodes with a cross-linkable hole transporting material

A cross-linkable hole transporting material PLEXCORE® HTL was incorporated in phosphorescent organic light emitting diodes. This hole transporting material is based on an arylamine derivate. The device performance in terms of efficiency and lifetime was compared to the same devices with a thermally evaporated 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB)-based hole transporting layer. The resulting devices with the cross-linkable HTL gave higher efficiency, smaller roll-off and longer lifetime compared with devices with the NPB-based devices. This new hole transporting material paves the road toward solution processed multilayer light emitting devices.     

Full coverage all-inorganic cesium lead halide perovskite film for high-efficiency light-emitting diodes assisted by 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene

A full coverage all-inorganic cesium lead halide perovskite CsPbBr₃ film is achieved by introducing a small organic molecule material, 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB), as a solution additive. The light-emitting diode (LED) using this CsPbBr₃:TmPyPB perovskite film as light emitting layer exhibit improved electroluminescent (EL) performance with the maximum brightness of 22309 cd/m², highest current efficiency of 8.77 cd/A, and external quantum efficiency (EQE) of 2.27%, which are 8.6, 10.2 and 10.3 times to that of neat CsPbBr₃ film based LED, respectively. The enhanced EL performances are ascribed to less current leakage due to full coverage, and improved electron transporting in the CsPbBr₃:TmPyPB perovskite film.     

Organometal halide perovskite as hole injection enhancer in organic light-emitting diode

We introduce an organometal halide perovskite (CH₃NH₃PbI₃), as a hole injection layer (HIL) to accelerate hole injection and transport in tris-(8-hydroxyquinoline) aluminum-based organic light-emitting diodes (OLEDs). The excellent charge mobility of CH₃NH₃PbI₃ along with the better interface contacts induced by the CH₃NH₃PbI₃ HIL improved the charge balance and thus enhanced device performance compared with that of OLEDs without a HIL and with a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) HIL. Maximum luminance of 19110 cd m⁻² and power efficiency of 3.210 lm W⁻¹ were obtained. Also, besides more balanced charge recombination, the non-aqueous fabrication of the perovskite HIL and the chemical stability of indium tin oxide in contact with CH₃NH₃PbI₃ led to increased device stability and durability, giving a half-life time as long as 31.7 h.     

高效叠层OLED白光器件进展

叠层有机发光二极管（Organic Light-Emitting Diode,OLED）白光器件具备低功耗、高亮度、高色域等性能优势。然而,由于效率、寿命及驱动电压等性能仍有较大改进空间,叠层结构的材料及电学结构仍需进一步优化。本文重点介绍叠层OLED白光器件的最新研究进展,总结了三类电荷产生层（Charge Generation Layer,CGL）在工程化应用中存在的问题以及其非破坏性检测方法;综述高效叠层OLED白光器件的“全磷光体系”、“并行通道激子收集”及“混合磷光热活性型延迟荧光（Thermally Activated Delayed Fluorescence,TADF）体系”最新研究成果,对器件寿命问题进行总结,探讨分析“分级掺杂”、“四色混合TADF体系”等从结构方面提出优化方案,并针对不同发光材料体系中的CGL材料及结构综述叠层OLED白光器件实现较低工作电压的技术方法,最后对叠层OLED白光器件的材料和结构提出改进建议。     

Modification effect of hole injection layer on efficiency performance of wet-processed blue organic light emitting diodes

We examined the performance of solution-processed organic light emitting diodes (OLEDs) by modifying the hole injection layer (HIL), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS). Atomic force microscopy (AFM) showed morphological changes with surface roughness (R_RMS) of 1.47, 1.73, and 1.37 nm for pristine PEDOT: PSS, PEDOT: PSS modified with a 40 v% deionized water and with a 30 v% acetone, respectively. The surface hydrophobicity of the acetone modified PEDOT:PSS HIL layer was decreased by 34% as comparing with the water modified counterpart. Electrical conductivity was increased to two orders of magnitude for the water and acetone modified PEDOT:PSS as compared to pristine. We observed a low refractive index and high transmittance for the modified HILs. We fabricated and explored electroluminescent properties of bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) based sky blue device by utilizing HIL with and without modification. The changes in electrical conductivity, surface roughness, refractive index, and transmittance of the modified HILs strongly influenced the performance of devices. By utilizing a 30% acetone modified HIL, the power efficiency was increased from 14.2 to 24.2 lm/W, an increment of 70% and the EQE from 8.5 to 13.1% at 100 cd/m², an increment of 54%. The maximum luminance also increased from 11,780 to 18,190 cd/m². The findings revealed herein would be helpful in designing and fabricating high efficiency solution processed OLEDs.     

Aqueous solution-processed InCl3 as an effective buffer layer to improve hole injection in simplified phosphorescent organic light emitting diodes

An effective anode buffer layer is demonstrated by aqueous solution-processed indium trichloride (sInCl₃) in simplified phosphorescent organic light emitting diodes (PhOLEDs). The hole injection is improved in sInCl₃ based PhOLEDs exhibiting better performance with decreased driving voltage, increased power efficiency compared to the traditional ultraviolet-ozone (UV-Ozone) treated ones. Then, the mechanism for the enhanced hole injection is investigated. Better electrode contact is found in sInCl₃ based hole dominated devices. Higher work function (∼0.60 eV) is detected on the sInCl₃-ITO anode and stable InCl bonds are formed on its surface compared to the UV-Ozone treated one according to the photoelectron spectroscopy.     

Thermally stable efficient hole transporting materials based on carbazole and triphenylamine core for red phosphorescent OLEDs

In this work, a series of hole transporting materials with carbazole and triphenylamine cores have been synthesized and characterized. In the carbazole's 3rd and 6th positions, two site tryphenylamine para positions are end capped with the same types of branching derivatives to compare the overall performances of constructed devices. All of our hole transporting materials showed good thermal stabilities without any crystallized features which expressed in higher decomposition temperature (Over 500 °C at 5% weight reduction). All synthesized materials revealed HOMO energy levels between −5.62 and −5.48 eV, which values are lying between HOMO energy values of anode and emission layer; as a result, it made an effective path for hole transportation. Higher lying LUMO values between −2.51 and −2.31 can block the electrons from adjacent layer to ensure the perfect recombination in the middle layer. Triphenylamine based HTMs indicated better performances than carbazole based HTMs. Further comparisons were done by using NPB as hole transporting material with the same red phosphorescent based OLED device. HTM2A based device IV was exhibited higher maximum current efficiency of 30.6 cd/A and higher maximum external quantum efficiency of 26.7% than reference NPB based device. Measured Hole mobility value of HTM2A with hole dominant device was 5.3 × 10⁻⁴ cm² V⁻¹ s⁻¹, which was better than NPB. Synthesized HTM2A would be a promising hole transporting material for various phosphorescent based OLEDs.     

Multilayer light emitting devices with organometal halide perovskite: Polymer composite emission layer: The relationship of device performance with the compositions of emission layer and device configurations

The formation of composite layers comprising polymers such as poly(ethylene oxide) (PEO) and organometal halide perovskites (Peros) is an effective way to improve the morphology integrity of Pero films and the performance of Pero light emitting devices. Herein, we report the influences of the ratio of the organic content to inorganic content in the precursors as well as the compositions of PEO: Pero films on their morphology, crystal structure and electroluminescent property. Multilayer Pero light emitting devices show the external quantum efficiency of ca. 4.0% and power efficiency of 7.9 lm W⁻¹.     

High efficiency phosphorescent white organic light-emitting diodes with an ultra-thin red and green co-doped layer and dual blue emitting layers

Phosphorescent white organic light emitting diodes (WOLEDs) with a multi-layer emissive structure comprising two separate blue layers and an ultra-thin red and green co-doped layer sandwiched in between have been studied. With proper host and dopant compositions and optimized layer thicknesses, high-performance WOLEDs having a power efficiency over 40 lm/W at 1000 cd/m² with a low efficiency roll-off have been produced. Through a systematic investigation of the exciton confinement and various pathways for energy transfer among the hosts and dopants, we have found that both the ultra-thin co-doped layer and two blue emitting layers play a vital role in achieving high device efficiency and controllable white emission.     

异质结堆叠发光层红色磷光有机发光二极管

本文采用主客体交错结构的发光层,即发光层是 由多组主体材料CBP和客体材料Ir(piq)₂(acac)异质结堆叠构成的。为了改善器件的性能 ,分别优化 了单主体层和单客体层的厚度。研 究表明,单主体层厚度为3~4 nm,单客体层厚度为0.3 nm时,器件能够获得的最大电流效率为3.92 cd/A,色纯度 和发光稳 定性俱佳,1mA工作电流下的CIE色坐标为(0.669,0.308),当工作电流从0.1 mA变化 到1mA,色度坐标的变化值(Δ(x,y)) 仅为(0.004,0.002)。所采用的 主客体交错发光层的制备方法,工艺简单,且因为能分别调整主客体层的厚度而改善因客体 分子聚集或因长程偶极子间相互作用对发光效率的影响,为非掺杂磷光有机发光二极管的制 备提供了思路。