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Fast spin-flip enables efficient and stable organic electroluminescence from charge-transfer states

DOI: 10.1038/s41566-020-0668-z DOI Help

Authors: Lin-song Cui (University of Cambridge) , Alexander J. Gillett (University of Cambridge) , Shou-feng Zhang (Guangxi University of Science and Technology; Georgia Institute of Technology) , Hao Ye (Kyushu University) , Yuan Liu (echnische Universität Dresden) , Xian-kai Chen (Georgia Institute of Technology) , Ze-sen Lin (Kyushu University) , Emrys W. Evans (University of Cambridge) , William K. Myers (Centre for Advanced Electron Spin Resonance (CAESR), University of Oxford) , Tanya K. Ronson (University of Cambridge) , Hajime Nakanotani (Kyushu University) , Sebastian Reineke (Technische Universität Dresden) , Jean-luc Bredas (Georgia Institute of Technology) , Chihaya Adachi (Kyushu University) , Richard H. Friend (University of Cambridge)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Nature Photonics , VOL 395

State: Published (Approved)
Published: August 2020
Diamond Proposal Number(s): 21497

Abstract: A spin-flip from a triplet to a singlet excited state, that is, reverse intersystem crossing (RISC), is an attractive route for improving light emission in organic light-emitting diodes, as shown by devices using thermally activated delayed fluorescence (TADF). However, device stability and efficiency roll-off remain challenging issues that originate from a slow RISC rate (kRISC). Here, we report a TADF molecule with multiple donor units that form charge-resonance-type hybrid triplet states leading to a small singlet–triplet energy splitting, large spin–orbit couplings, and a dense manifold of triplet states energetically close to the singlets. The kRISC in our TADF molecule is as fast as 1.5 × 107 s−1, a value some two orders of magnitude higher than typical TADF emitters. Organic light-emitting diodes based on this molecule exhibit good stability (estimated T90 about 600 h for 1,000 cd m−2), high maximum external quantum efficiency (>29.3%) and low efficiency roll-off (<2.3% at 1,000 cd m−2).

Journal Keywords: Electronics, photonics and device physics; Lasers, LEDs and light sources; Materials chemistry; Materials for devices

Subject Areas: Physics, Materials

Instruments: I19-Small Molecule Single Crystal Diffraction

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