High Efficiency Fluorescent Electroluminescence with Extremely Low Efficiency Roll‐Off Generated by a Donor–Bianthracene–Acceptor Structure: Utilizing Perpendicular Twisted Intramolecular Charge Transfer Excited State

Abstract

AbstractAlthough phosphorescent and thermally activated delayed fluorescence (TADF) emitters can break through the spin statistics rules and achieve nearly 100% radiative exciton production (ηr), the swift efficiency roll‐off as luminance increases due to the accumulation of lowest triplet excited states with relatively long lifetime is the fatal bottleneck for their lighting application. How to achieve high ηr and low efficiency roll‐off simultaneously is still a challenge. To address this issue, two metal‐free organic molecules are reported with a highly twisted donor–bianthracene–acceptor structure involving high‐lying twisted intramolecular charge transfer (TICT) intermediate excited states, by which electroluminescent (EL) devices with both high ηr and extremely low efficiency roll‐off could be realized. Significant low efficiency roll‐off is achieved with about 99.1% of the maximum external quantum efficiency (EQE) maintained even at a high current density of 100 mA cm−2, corresponding to luminance of 23615 cd m−2, along with maximum EQE of 7.13% (ηr of 64.82%) in a doped green EL device with 9‐(4‐{10′‐[4‐(4,6‐diphenyl‐[1,3,5]triazin‐2‐yl)‐phenyl]‐[9,9′]bianthracenyl‐10‐yl}‐phenyl)‐9H‐carbazole as a host. The state‐of‐the‐art low efficiency roll‐off and enhanced ηr would be attributed to spin mixing of high‐lying TICT singlet and triplet intermediate excited states, proving the great potential of such a host design strategy for their practical lighting application.