Alternative p-doped hole transport material for low operating voltage and high efficiency organic light-emitting diodes
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We investigate the properties of N,N'-[(Diphenyl-N,N'-bis) 9,9,-dimethyl-fluoren-2-yl]-benzidine (BF-DPB) as hole transport material (HTL) in organic light-emitting diodes (OLEDs) and compare BF-DPB to the commonly used HTLs N,N,N',N'-tetrakis(4-methoxyphenyl)-benzidine (MeO-TPD), 2,2',7,7'-tetrakis(N,N'-di-p-methylphenylamino)-9,9'-spirobifluorene (Spiro-TTB), and N, N'-di(naphtalene-1-yl)-N,N'-diphenylbenzidine (NPB). The influence of 2,2'-(perfluoronaphthalene-2,6-diylidene)dimalononitrile (F6-TCNNQ p-dopant) concentration in BF-DPB on the operation voltage and efficiency of red and green phosphorescent OLEDs is studied; best results are achieved at 4 wt. % doping. Without any light extraction structure, BF-DPB based red (green) OLEDs achieve a luminous efficacy of 35.1 lm/W (74.0 lm/W) at 1000 cd/m(2) and reach a very high brightness of 10 000 cd/m(2) at a very low voltage of 3.2 V (3.1 V). We attribute this exceptionally low driving voltage to the high ionization potential of BF-DPB which enables more efficient hole injection from BF-DPB to the adjacent electron blocking layer. The high efficiency and low driving voltage lead to a significantly lower luminous efficacy roll-off compared to the other compounds and render BF-DPB an excellent HTL material for highly efficient OLEDs.
Murawski , C , Fuchs , C , Hofmann , S , Leo , K & Gather , M C 2014 , ' Alternative p-doped hole transport material for low operating voltage and high efficiency organic light-emitting diodes ' Applied Physics Letters , vol 105 , no. 11 , 113303 . DOI: 10.1063/1.4896127
Applied Physics Letters
Copyright 2014 AIP Publishing LLC. Alternative p-doped hole transport material for low operating voltage and high efficiency organic light-emitting diodes Murawski, C., Fuchs, C., Hofmann, S., Leo, K. & Gather, M. C. 15 Sep 2014 In : Applied Physics Letters. 105, 11, 5 p.113303 available from http://scitation.aip.org/content/aip/journal/apl/105/11/10.1063/1.4896127
This work received funding from the European Community Seventh Framework Programme under Grant Agreement No. FP7 267995 (NUDEV) and from the European Social Fund and the free state of Saxony through the OrganoMechanics project.
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