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Blue organic light-emitting diodes realizing external quantum efficiency over 25%
using thermally activated delayed fluorescence emitters
#MMPMID28325941
Miwa T
; Kubo S
; Shizu K
; Komino T
; Adachi C
; Kaji H
Sci Rep
2017[Mar]; 7
(1
): 284
PMID28325941
show ga
Improving the performance of blue organic light-emitting diodes (OLEDs) is needed
for full-colour flat-panel displays and solid-state lighting sources. The use of
thermally activated delayed fluorescence (TADF) is a promising approach to
efficient blue electroluminescence. However, the difficulty of developing
efficient blue TADF emitters lies in finding a molecular structure that
simultaneously incorporates (i) a small energy difference between the lowest
excited singlet state (S(1)) and the lowest triplet state (T(1)), ?E (ST), (ii) a
large oscillator strength, f, between S(1) and the ground state (S(0)), and (iii)
S(1) energy sufficiently high for blue emission. In this study, we develop TADF
emitters named CCX-I and CCX-II satisfying the above requirements. They show blue
photoluminescence and high triplet-to-singlet up-conversion yield. In addition,
their transition dipole moments are horizontally oriented, resulting in further
increase of their electroluminescence efficiency. Using CCX-II as an emitting
dopant, we achieve a blue OLED showing a high external quantum efficiency of
25.9%, which is one of the highest EQEs in blue OLEDs reported previously.
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