Suppression of Dexter transfer by covalent encapsulation for efficient matrix-free narrowband deep blue hyperfluorescent OLEDs

Hwan-Hee Cho, Daniel G. Congrave*, Alexander J. Gillett, Stephanie Montanaro, Haydn E. Francis, Victor Riesgo-Gonzalez, Junzhi Ye, Rituparno Chowdry, Weixuan Zeng, Marc K. Etherington, Jeroen Royakkers, Oliver Millington, Andrew D. Bond, Felix Plasser, Jarvist M. Frost, Clare P. Grey, Akshay Rao, Richard H. Friend, Neil C. Greenham*, Hugo Bronstein*

*Corresponding author for this work

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Abstract

Hyperfluorescence shows great promise for the next generation of
commercially feasible blue organic light-emitting diodes, for which
eliminating the Dexter transfer to terminal emitter triplet states is key to
efficiency and stability. Current devices rely on high-gap matrices to prevent
Dexter transfer, which unfortunately leads to overly complex devices from
a fabrication standpoint. Here we introduce a molecular design where
ultranarrowband blue emitters are covalently encapsulated by insulating
alkylene straps. Organic light-emitting diodes with simple emissive layers
consisting of pristine thermally activated delayed fluorescence hosts doped
with encapsulated terminal emitters exhibit negligible external quantum
efficiency drops compared with non-doped devices, enabling a maximum
external quantum efficiency of 21.5%. To explain the high efficiency in the
absence of high-gap matrices, we turn to transient absorption spectroscopy.
It is directly observed that Dexter transfer from a pristine thermally
activated delayed fluorescence sensitizer host can be substantially reduced
by an encapsulated terminal emitter, opening the door to highly efficient
‘matrix-free’ blue hyperfluorescence.
Original languageEnglish
Number of pages17
JournalNature Materials
Early online date13 Mar 2024
DOIs
Publication statusE-pub ahead of print - 13 Mar 2024

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