pengyuhaopeng

Publication date: December 2017
Source:Vacuum, Volume 146
Author(s): Gopeeka Rajan, Vandana Yadav, Payal Manzhi, Gayatri Chauhan, C.K. Suman, Ritu Srivastava, O.P. Sinha
1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) molecule have been studied as hole injection layer for application in organic semiconductor based devices with potential to modify the electronic properties of electrodes due to its strong electron-withdrawing property. Thermally stable hole transport material 2, 7-bis [N, N-bis (4-methoxy-phenyl) amino]-9, 9-spirobifluorene (MeO-Spiro-TPD) has been used to fabricate hole only devices. To make the injection efficient at metal/organic interface and to reduce the driving voltage of the organic devices, the interface has been modified with a thin layer of highly electron accepting HAT-CN material. Modified interface has been investigated at a different range of thicknesses of HAT-CN. This interface modification resulted in the switching of injection limited transport to space charge limited conduction mechanism with the introduction of HAT-CN layer at metal/organic interfaces. The hole injection property has been found to increase with an increase in HAT-CN thickness. When these modified substrates were used as a hole injecting contacts in organic light emitting diodes (OLEDs), they have shown an increase in current density and device efficiency.

Publication date: April 2018
Source:Microelectronics Reliability, Volume 83
Author(s): Deepak Kumar Dubey, Meenu Singh, Snehasis Sahoo, Jwo-Huei Jou
High-efficiency white emission is crucial to the design of energy-saving display and lighting panels, whereas solution-process feasibility is highly desirable for large area-size and cost-effective roll-to-roll manufacturing. In this study, we demonstrate highly-efficient, bright and chromaticity stable white organic light emitting diodes (OLEDs) with solution-processed single emissive layer. The resultant best white OLED shows excellent electroluminescence performance with forward-viewing external quantum efficiency, current efficiency and power efficiency of 22.7%, 48.8cdA⁻¹ and 27.8lmW⁻¹ at 100cdm⁻², respectively, with a maximum luminance of 19,590cdm⁻². Furthermore, we also observed an increment of 112% in the power efficiency, 86.9% in the current efficiency and a decrement of 39.2% in the external quantum efficiency at 100cdm⁻² as the doping concentration of blue dye was increased from 10wt% to 25wt% in the devices. The better efficiency performance may be attributed to the effective exciton-confining device architecture and low-energy barrier for electrons to inject from the hole-blocking electron-transport layer to the host layer.

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Publication date: November 2017
Source:Organic Electronics, Volume 50
Author(s): Chunxiu Zang, Xiaomei Peng, Hui Wang, Ziwei Yu, Letian Zhang, Wenfa Xie, Hongyu Zhao
Efficient multilayer (ML) and single layer (SL) phosphorescent organic light-emitting devices (PHOLEDs) with a bipolar host 9,9′-[4′-(2-ethyl-1H-benzimidazol-1-yl) [1,1′-biphenyl]-3,5-diyl] bis-H-Carbazole (EBBPC) are fabricated. The photophysical, electrochemical and carrier transporting properties of EBBPC host are investigated. The maximum external quantum efficiency (EQE) can reach 14.9%, 15.6%, 16.0% and 15.4% for red (R), green (G), blue (B), and white ML-PHOLEDs, respectively. And the maximum EQE can also reach 10.1%, 14.6% and 9.8% for R, G, and B SL-PHOLEDs, respectively. Besides, the SL-PHOLEDs show low efficiency roll-off due to the broader exciton formation zone in SL OLEDs. The excellent performance of ML- and SL-PHOLEDs could be attributed to the balanced bipolar transporting properties and appropriate energy level of the host.

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Publication date: November 2017
Source:Organic Electronics, Volume 50
Author(s): Tanmay Chatterjee, Wen-Yi Hung, Wei-Feng Tang, Hsiao-Fan Chen, Ken-Tsung Wong
Three new bipolar molecules composed of carbazole, triarylamine, and bipyridine were synthesized and utilized as host materials in multi-color phosphorescent OLEDs (PhOLEDs). These carbazole-based materials comprise a hole-transport triarylamine at C3 and an electron-transport 2,4′- or 4,4′-bipyridine at N9. The different bipyridine isomers and linking topology of the bipyridine with respect to carbazole N9 not only allows fine-tuning of physical properties but also imparts conformational change which subsequently affects molecular packing and carrier transport properties in the solid state. PhOLEDs were fabricated using green [(ppy)2Ir(acac)], yellow [(bt)2Ir(acac)], and red [(mpq)2Ir(acac)] as doped emitters, which showed low driving voltage, high external quantum efficiency (EQE), and extremely low efficiency roll-off. Among these new bipolar materials, the 2Cz-44Bpy-hosted device doping with 10% (ppy)2Ir(acac) as green emitting layer showed a high EQE of 22% (79.8 cd A⁻¹) and power efficiency (PE) of 102.5 lm W⁻¹ at a practical brightness of 100 cd m⁻². In addition, the device showed limited efficiency roll-off (21.6% EQE) and low driving voltage (2.8 V) at a practical brightness of 1000 cd m⁻².

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Publication date: November 2017
Source:Organic Electronics, Volume 50
Author(s): Youming Zhang, Zheng Yin, Fanyuan Meng, Junting Yu, Caifa You, Shengyi Yang, Hua Tan, Weiguo Zhu, Shijian Su
Two novel tetradentate platinum (II) 3,6-substituted salophen complexes of Pt-2 and Pt-3 were synthesized and characterized, in which the substituted group is a donor (D) unit of 4,4′-di(tert-butyl)triphenylamine (Bu^tTPA) for Pt-2 and a donor-acceptor (D-A) framework of Bu^tTPA and benzothiadiazole (BT) for Pt-3. Their thermal, optophysical, electrochemical and electroluminescent properties were primarily investigated. It is found that the emission for this type of tetradentate platinum (II) complexes is tuned from deep red to near infrared by appending D-A framework under photo-excitation. As a result, Pt-3 presented a significant near infrared electroluminescence peaked at 703 nm in its doped polymer light-emitting devices (PLEDs). The maximum external quantum efficiency of 0.88% is observed in the Pt-3 doped PLEDs using a blend of poly(vinylcarbazole) and 1,3-bis(5-(4-(tert-butyl)phenyl)-1,3,4-oxadiazol-2-yl) benzene as the host matrix. Our work indicates that appending D-A framework into tetradentate Pt(II) salophen complex is a useful strategy to get high-performance near infrared emission for this type of tetradentate Pt (II) complexes.

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