Blue organic light-emitting diodes realizing external quantum efficiency over 25% using thermally activated delayed fluorescence emitters.
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 (S1) and the lowest triplet state (T1), ΔEST, (ii) a large oscillator strength, f, between S1and the ground state (S0), and (iii) S1energy 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.
Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011, Japan.
Takuya
T
Miwa
Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011, Japan.
Shosei
S
Kubo
Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011, Japan.
Katsuyuki
K
Shizu
Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka, 819-0395, Japan.
Takeshi
T
Komino
Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka, 819-0395, Japan.|JST, ERATO, Adachi Molecular Exciton Engineering Project, 744 Motooka, Nishi, Fukuoka, 819-0395, Japan.
Chihaya
C
Adachi
Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011, Japan. kaji@scl.kyoto-u.ac.jp.|JST, ERATO, Adachi Molecular Exciton Engineering Project, 744 Motooka, Nishi, Fukuoka, 819-0395, Japan. kaji@scl.kyoto-u.ac.jp.
Hironori
H
Kaji