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Highly Simplified Tandem Organic Light-emitting Devices Incorporating a Green Phosphorescence Ultrathin Emitter within a Novel Interface Exciplex for High Efficiency Ting Xu, Jun-Gui Zhou, Chen-Chao Huang, Lei Zhang, Man Keung Fung, Imran Murtaza, Hong Meng, and Liang-Sheng Liao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b16094 • Publication Date (Web): 08 Mar 2017 Downloaded from http://pubs.acs.org on March 9, 2017
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ACS Applied Materials & Interfaces
Highly Simplified Tandem Organic Light-Emitting Devices Incorporating a Green Phosphorescence Ultrathin Emitter within a Novel Interface Exciplex for High Efficiency Ting Xua,b, Jun-Gui Zhoua, Chen-Chao Huanga, Lei Zhanga, Man-Keung Funga, Imran Murtazac,d, Hong Mengb,c* and Liang-Sheng Liaoa* a
Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute
of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou, Jiangsu 215123, China b
School of Advanced Materials, Shenzhen Graduate School, Peking University,
Shenzhen 518055, China c
Key Laboratory of Flexible Electronics and Institute of Advanced Materials, Jiangsu
National Synergistic Innovation Centre for Advanced Materials, Nanjing Tech University, Nanjing 211816, China d
Department of Physics, International Islamic University, Islamabad 44000, Pakistan
KEYWORDS Organic light-emitting diodes, Tandem structure, Interface exciplex, Ultrathin emissive layers, Current efficiency
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ABSTRACT
Herein, we report a novel design philosophy of tandem OLEDs incorporating a doping-free green phosphorescent Bis[2-(2-pyridinyl-N)phenyl-C](acetylacetonato) iridium(III) (Ir(ppy)2(acac) ) as ultrathin emissive layer (UEML) into a novel interface-exciplex-forming cyclohexane
(TAPC)
and
structure
of
1,1-Bis[(di-4-tolylamino)
1,3,5-tri(p-pyrid-3-yl-phenyl)benzene
phenyl]
(TmPyPB).
Particularly, relatively low working voltage and remarkable efficiency are achieved and the designed tandem OLEDs obtain a peak current efficiency of 135.74 cd/A (EQE=36.85 %) which is two times higher than 66.2 cd/A (EQE=17.97 %) of the device with a single emitter unit. This might be one of the highest efficiencies of OLEDs applying ultrathin emitters without light extraction. Moreover, with the proposed structure, the color gamut of the displays can be effectively increased from 76 % to 82 % NTSC if the same red and blue emissions as those in the NTSC are applied. A novel form of harmonious fusion among interface exciplex, UEML, and tandem structure is successfully realized, which shed light on further development of ideal OLEDs structure with high efficiency, simplified fabrication, low power consumption, low cost and improved color gamut, simultaneously.
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ACS Applied Materials & Interfaces
1. Introduction After the invention of first succinct organic light-emitting device (OLED) with twolayer structure in 1987 by C.W Tang,1 flat-panel displays and illumination applications based on OLED technology have developed sharply due to their attractive features such as simple fabrication process, devisable smart structure, impressive color rendering, ultra-thin structure, wide viewing angles, abundant organic materials, light-weight and high compatibility with flexible substrates.2-9 OLEDs stacking by two or more emitter units have drawn enormous attention due to their impressive current efficiency (CE), brightness, external quantum efficiency (EQE), luminous efficiency, and device life time
compared
to
conventional
OLEDs.10-14
However,
stacking
multiple
electroluminescence (EL) units in tandem OLEDs increases driving voltage and complicates fabrication process relative to their standard single unit counterparts. Moreover, commercial OLED products are still so pricey for consumers.15 Therefore it is urgently needed to boil down the OLEDs structure and fabrication technology to reduce the cost of products.15 To be specific, in typical tandem OLEDs, the doping technique needs the careful selection of appropriate hosts for different dopants in hostguest emitter system.16 Besides, the controlment of codeposition rate and dopant concentration in the fabrication procedure is complex and not absolutely accurate, which tends to lower the yield in production line. Moreover, the physical vapor deposition equipment needs to be remoulded with adequate sensors and evaporator sources in order to realize complex device fabrication of tandem OLEDs, which increase their manufacturing costs. 3
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To loosen the bottlenecks, the doping-free technology applying ultrathin emitting nanolayers (
