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“Trade‐Off” Hidden in Condensed State Solvation: Multiradiative Channels Design for Highly Efficient Solution‐Processed Purely Organic Electroluminescence at High Brightness
Author(s) -
Cai Xinyi,
Chen Dongjun,
Gao Kuo,
Gan Lin,
Yin Qingwu,
Qiao Zhenyang,
Chen Zijun,
Jiang Xiaofang,
Su ShiJian
Publication year - 2018
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201704927
Subject(s) - oled , intersystem crossing , materials science , common emitter , singlet state , electroluminescence , triplet state , dopant , optoelectronics , excited state , brightness , quenching (fluorescence) , solvation , photon upconversion , fluorescence , photochemistry , luminescence , atomic physics , doping , nanotechnology , chemistry , optics , physics , layer (electronics) , ion , organic chemistry
Actualizing highly efficient solution‐processed thermally activated delayed fluorescent (TADF) organic light‐emitting diodes (OLEDs) at high brightness becomes significant to the popularization of purely organic electroluminescence. Herein, a highly soluble emitter benzene‐1,3,5‐triyltris((4‐(9,9‐dimethylacridin‐10(9 H )‐yl)phenyl)methanone was developed, yielding high delayed fluorescence rate ( k TADF > 10 5 s −1 ) ascribed to the multitransition channels and tiny singlet–triplet splitting energy (Δ E ST ≈ 32.7 meV). The triplet locally excited state is 0.38 eV above the lowest triplet charge‐transfer state, assuring a solely thermal equilibrium route for reverse intersystem crossing. Condensed state solvation effect unveils a hidden “trade‐off”: the reverse upconversion and triplet concentration quenching processes can be promoted but with a reduced radiative rate from the increased dopant concentration and the more polarized surroundings. Striking a delicate balance, corresponding vacuum‐evaporated and solution‐processed TADF‐OLEDs realized maximum external quantum efficiencies (EQEs) of ≈26% and ≈22% with extremely suppressed efficiency roll‐off. Notably, the wet‐processed one achieves to date the highest EQEs of 20.7%, 18.5%, 17.1%, and 13.6%, among its counterparts at the luminance of 1000, 3000, 5000, and 10 000 cd m −2 , respectively.