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

Journal article

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).

Authors: Cui, L-S; Gillett, AJ; Zhang, S-F; Ye, H; Liu, Y

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Springer Nature
• Journal: Nature Photonics
• Volume: 14
• Issue: 10
• Pages: 636–642
• Publication date: 2020-08-03
• Acceptance date: 2020-06-26
• DOI: 10.1038/s41566-020-0668-z
• EISSN: 1749-4893
• ISSN: 1749-4885
• Language: English
• Keywords: FFR