What They Say
Scientists from Kyushu and Kwanse Gakuin Universities have released through a paper in ‘Nature’, with support from Kyulux and JNC Petrochemical Corp, details of a new blue material based on TADF that has CIE colour coordinates of (0.13,0.16) with EQE of 32% at 1,000 cd/m². The emitted light has a FWHM of 19nm and a LT95 of 18 hours at 1,000 cd/m².
The design is based on a two-unit stacked tandem hyperfluorescence OLED with improved singlet-excited-state energy transfer from a sky-blue assistant dopant exhibiting thermally activated delayed fluorescence (TADF) called hetero-donor-type TADF(HDT-1) to a pure-blue emitter. With stricter control of device fabrication and procedures it is expected that device lifetimes will further improve to rival commercial fluorescent blue OLEDs.
“Three-fourths of electrical charges combine to form energy states called triplets in OLEDS, and TADF molecules can convert these nonemitting triplets into light-emitting singlets,” Masaki Tanaka, an OPERA (Center for Organic Photonics and Electronics Research) researcher who worked closely with Chan on the study told Photonics.com. “However, v-DABNA is somewhat slow at converting the high-energy triplets, which often play a role in degradation. To get rid of the dangerous triplets more quickly, we included an intermediary TADF molecule that can more rapidly convert triplets into singlets.”
What We Think
Lifetime remains a challenge, but progress continues in trying to solve the blue problem for OLED materials. I’ve been reporting on this topic on and off for twenty five years and made myself ‘persona non grata’ with CDT, a pioneer in polymer OLEDs in the UK that eventually was bought by Sumitomo when at a press conference designed to build hype around OLED, I asked ‘what about blue?’. Now, huge progress has been made, but I’m not holding my breath, yet.
In the past, Kyulux CEO Jun Adachi has said that the target for the blue emitter material, needed for a commercial customer, is 700 hours (T95). (BR)
