“Trade‐Off” Hidden in Condensed State Solvation: Multiradiative Channels Design for Highly Efficient Solution‐Processed Purely Organic Electroluminescence at High Brightness

• DOI: 10.1002/adfm.201704927
• Publication Date: 2017-12-08T10:48:47Z
• Authors: Xinyi Cai; Dongjun Chen; Kuo Gao; Lin Gan; Qingwu Yin; Zhenyang Qiao; Zijun Chen; Xiaofang Jiang; Shi‐Jian Su
• Keywords: Intersystem crossing; Photon Upconversion

Abstract 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 electroluminescence. Herein, a soluble emitter benzene‐1,3,5‐triyltris((4‐(9,9‐dimethylacridin‐10(9 H )‐yl)phenyl)methanone was developed, yielding fluorescence rate ( k TADF > 10 5 s −1 ) ascribed multitransition channels and tiny singlet–triplet splitting energy (Δ E ST ≈ 32.7 meV). The triplet locally excited state is 0.38 eV above lowest charge‐transfer state, assuring solely thermal equilibrium route for reverse intersystem crossing. Condensed solvation effect unveils hidden “trade‐off”: upconversion concentration quenching processes can be promoted but with reduced radiative from increased dopant more polarized surroundings. Striking delicate balance, corresponding vacuum‐evaporated TADF‐OLEDs realized maximum external quantum efficiencies (EQEs) ≈26% ≈22% extremely suppressed efficiency roll‐off. Notably, wet‐processed one achieves date highest EQEs 20.7%, 18.5%, 17.1%, 13.6%, among its counterparts luminance 1000, 3000, 5000, 000 cd m −2 , respectively.