Matrix-free hyperfluorescent organic light-emitting diodes: opportunities and challenges
Hwan-Hee Cho a, Dan G. Congrave b, Hugo Bronstein b, Neil C. Greenham a
a Department of Physics, Cavendish Laboratory, University of Cambridge; Cambridge, UK
b Department of Chemistry, University of Cambridge, UK
nanoGe Fall Meeting
Proceedings of Materials for Sustainable Development Conference (MAT-SUS) (NFM22)
#OPTONEXT - Next Gen Semiconductors for Optoelectronics
Barcelona, Spain, 2022 October 24th - 28th
Poster, Hwan-Hee Cho, 244
Publication date: 11th July 2022

For realising better device stability and colour purity, efficient thermally activated delayed fluorescence (TADF) materials have been widely studied as exciton donors for fluorescent acceptors. Highly efficient hyperfluorescent organic light-emitting diodes (OLEDs) have been reported exploiting a variety of combinations of TADF donors and fluorescent acceptors embedded into high-gap host matrices. However, it should be taken into account that the host matrix can reduce power efficiency, resulting from a considerable increase in driving voltage. Furthermore, a three-component composition in an emitting layer (EML) also increases the complexity of device fabrication beyond the typical host-guest emissive layer adopted by industry. So far, wide-gap host matrices have been considered practically essential to dilute TADF and fluorescent molecules and suppress two challenging energy loss mechanisms, 1) Aggregation/ concentration quenching of TADF donors and 2) Triplet Dexter energy transfer between TADF donors and fluorescent acceptors. In principle, the EML of hyperfluorescent OLEDs only requires two components: a TADF host and a fluorescent emitter, a simpler device structure that is termed matrix-free hyperfluorescence (MFHF). If the host matrix could be removed without the efficiency loss, more efficient and simple-structured MFHF OLEDs could be realised. In this presentation, new strategies are explored to suppress the main loss pathways associated with hyperfluorescent devices to preclude the need for a high-gap co-host. Firstly, novel organometallic TADF compounds (so-called carbene-metal-amides (CMAs)) are explored as efficient TADF hosts resistant to concentration quenching. Secondly, sterically encapsulated fluorescent acceptors are introduced to prevent close contact between the donors and acceptors and minimise Dexter triplet transfer energy loss in MFHF OLEDs.

George and Lilian Schiff Foundation, Rank Prize, ERC

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