Bright, efficient, and stable pure-green hyperfluorescent organic light-emitting diodes by judicious molecular design.

To fulfill ultra-high-definition display, efficient and bright green organic light-emitting diodes with Commission Internationale de l'Éclairage y-coordinate ≥ 0.7 are required. Although there are some preceding reports of highly efficient devices based on pure-green multi-resonance emitters, the efficiency rolloff and device stabilities for those pure-green devices are still unsatisfactory. Herein, we report the rational design of two pure-green multi-resonance emitters for achieving highly stable and efficient pure-green devices with CIE x,y s that are close to the NTSC and BT. 2020 standards. In this study, our thermally activated delayed fluorescence OLEDs based on two pure-green multi-resonance emitters result in CIE y up to 0.74. In hyperfluorescent device architecture, the CIE x s further meet the x-coordinate requirements, i.e., NTSC (0.21) and BT. 2020 (0.17), while keeping their CIE y s ~ 0.7. Most importantly, hyperfluorescent devices display the high maximum external quantum efficiencies of over 25% and maximum luminance of over 10 5  cd m -2 with suppressed rolloffs (external quantum efficiency of ~20% at 10 4  cd m -2 ) and long device stabilities with LT 95 s of ~ 600 h.