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Enhanced Electroluminescence Efficiency of Phosphorescent Organic Light-Emitting Diodes by Controlling the Triplet Energy of the Hole-Blocking Layer

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7 Author(s)
Park, Young Wook ; Display & Nanosystem Lab., Korea Univ., Seoul, South Korea ; Kim, Young Min ; Choi, Jin Hwan ; Park, Tae Hyun
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This letter reports on the effect of the triplet energy (E T) of the hole-blocking layer (HBL) on triplet exciton quenching between the emissive layer (EML) host and the HBL of phosphorescent organic light-emitting diodes (PHOLEDs). Using different EML hosts and HBLs having different E T's and electron mobilities, the effects of the E T's of the HBL have been analyzed. When the E T of the HBL is lower than that of the EML host, the PHOLEDs show significant dependence of reduced device performances. PHOLEDs having a 3-(4-biphenylyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole HBL show 65% improved external quantum efficiency (EQE) at 500 cd/m2 with a 4, 4',4"-tris( N-carbazolyl)-triphenyl-amine host than that with an N,N' -dicarbazolyl-4-4''biphenyl host, while PHOLEDs having a 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline HBL show 41% reduced EQE. To solve the remaining key issue of developing highly efficient PHOLEDs, the E T of matching the EML and the HBL is extremely desirable and is also explored.

Published in:

Electron Device Letters, IEEE  (Volume:31 ,  Issue: 5 )