Researchers from Shenzhen University and Wuhan University have designed new white OLED devices that exhibit exceptional power efficiency (over 190 lm/W, 39% EQE) and extended operational lifetime (LT80 446 hours at 1,000 cd/m2).
The new device uses a blue TADF emitter emitter combined with a yellow MR-TADF emitter. The light is a warm white light. The researchers also used the same technique to create a standard white emission device, that still achieves a high EQE of 35.6%, thus further validating the strategy.
The researchers explain why the combination of the TADF and MR-TADF emitters results in such high performance devices. The blue D-A type TADF emitters, characterized by high kRISC, efficiently drive the up-conversion of triplet excitons. A fraction of these excitons undergo radiative transitions, leading to blue light emission, while the remaining excitons swiftly undergo Förster-type energy transfer (FET) to access the S1 state of yellow MR-TADF emitters. Subsequently, taking advantage of the higher kr of yellow MR-TADF emitters, they promptly engage in radiative transition, emitting the yellow component. This orchestrated process harmonizes triplet up-conversion and singlet radiation, ensuring efficient utilization of excitons to achieve dual objectives of enhancing both efficiency and stability.
