Blue OLED emitter TPh-BDBF reaches 28.4% EQE and triples lab device lifetime
Teams from Gyeongsang and Kyung Hee universities and Samsung Display made a blue emitter that keeps color purity; test devices lasted about three times longer than the reference.
A team led by Professor Kim Yun-hee of the Department of Chemistry at Gyeongsang National University, together with Professor Kim Tae-kyung's group at Kyung Hee University and Samsung Display, developed TPh-BDBF, an emitter for blue organic light-emitting diodes, according to veritas-a.com. Laboratory devices with it reached a maximum external quantum efficiency (EQE) of 28.4%, and their lifetime was about three times that of devices with the reference material t-DABNA veritas-a.com
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Device results
In a thermally activated delayed fluorescence (TADF) OLED with 5 wt% emitter, the maximum EQE was 28.4%, against 18.0% for t-DABNA at the same concentration veritas-a.com
veritas-a.comveritas-a.comOpen source ↗. Raising the emitter concentration from 1 to 5 wt% kept the full width at half maximum near 22 nm. In solution the emitter produced blue light at 460 nm with an 18 nm width.
Stability was tested in phosphor-sensitized fluorescence (PSF) devices, where a phosphorescent sensitizer passes energy to TPh-BDBF. At 1 wt%, the PSF device showed a maximum EQE of 27.0% and CIE coordinates of about (0.13, 0.11). The time to fall to 80% of the initial brightness of 1000 cd/m² (LT80) was 53.1 hours, versus 17.5 hours for t-DABNA veritas-a.com
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Molecular design
Multi-resonance TADF (MR-TADF) emitters have narrow spectra and high color purity, but their planar molecules interact strongly. This causes concentration quenching, while hole trapping and unwanted energy transfer limit device life. The team attached bulky ortho-terphenyl amine substituents to a dibenzofuran core to tune the electronic structure of the emitting center. Strongly twisted outer groups shield it in three dimensions.
Single-crystal analysis and molecular dynamics simulations showed that these groups keep the emitting cores apart. Device measurements and energy transfer analysis showed less hole trapping and less short-range Dexter transfer than with t-DABNA veritas-a.com
veritas-a.comveritas-a.comOpen source ↗. The results were published in Chemical Engineering Journal (Elsevier); the first authors are Cheon Hyeong-jin and Hwang Ji-hun.
