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Frontiers of Optoelectronics

Front Optoelec    2013, Vol. 6 Issue (4) : 435-439     DOI: 10.1007/s12200-013-0349-3
RESEARCH ARTICLE |
A simple unilateral homogenous PhOLEDs with enhanced efficiency and reduced efficiency roll-off
Shaoqing ZHUANG, Wenzhi ZHANG, Xiao YANG, Lei WANG()
Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China
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Abstract

In this paper, highly efficient phosphorescent organic lighting emitting diodes (PhOELDs) with low efficiency roll-off are demonstrated by using a unilateral homogenous device structure with wide band-gap material 4, 4', 4″-tri(N-carbazolyl)-triphenylamine (TCTA) as hole transporting layer and emitting layer (EML). The optimized blue device exhibits a high power efficiency of 40 lm/W, external quantum efficiency of 19.2% and current efficiency of 37.7 cd/A. More importantly, the device exhibits a low efficiency roll-off at 1000 cd/m2. In addition, the white homogenous PhOLEDs only exhibits the efficiency roll-off 5.6% and 17.5%, corresponding to the brightness of 1000 and 5000 cd/m2 respectively. These interesting results demonstrate that the simple unilateral homogenous device structure is a promising way to enhance the device efficiency and reduce the efficiency roll-off.

Keywords enhance efficiency      efficiency roll-off      unilateral homogenous structures     
Corresponding Authors: WANG Lei,Email:wanglei@mail.hust.edu.cn   
Issue Date: 05 December 2013
 Cite this article:   
Shaoqing ZHUANG,Wenzhi ZHANG,Xiao YANG, et al. A simple unilateral homogenous PhOLEDs with enhanced efficiency and reduced efficiency roll-off[J]. Front Optoelec, 2013, 6(4): 435-439.
 URL:  
http://journal.hep.com.cn/foe/EN/10.1007/s12200-013-0349-3
http://journal.hep.com.cn/foe/EN/Y2013/V6/I4/435
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Shaoqing ZHUANG
Wenzhi ZHANG
Xiao YANG
Lei WANG
Fig.1  Absorption (Abs) spectra of FIrpic and orange ((fbi)Ir(acac)); photoluminescence (PL) spectra of pure TCTA, FIrpic and orange doped TCTA and FIrpic
Fig.2  Structure and energy levels of unilateral homogenous device (device 1) and control device (device 2). ITO: indium tin oxide; HOMO: highest occupied molecular orbital; LUMO: lowest unoccupied molecular orbital
Fig.3  (a) curves of the devices 1 and 2; (b) current efficiency of unilateral homogenous device (device 1) and control device (device 2) at different brightness. Inset: EL spectrum of unilateral homogenous device (device 1) and control device (device 2)
Va)EQEmaxLEmaxLE1000 cd/m2LE 5000 cd/m2LE 10000 cd/m2
blue/TCTA2.8/6.519.137.734.227.119.1
blue/NPB3.0/7.114.528.423.915.47.8a)
white/TCTA3.0/9.715.940.838.734.030.3
white/NPB3.1/7.015.135.832.825.113.1
Tab.1  EL performance of blue and white PhOLEDs at different conditions
Fig.4  Thickness of excition recombination zone in homogenous device
Fig.5  Current efficiency of white PhOLED with homogenous structure and control structure. Inset: EL spectrum of different device structures
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