Donor Extension on Spiro-Acridine Enables Highly Efficient TADF-OLEDs with Relieved Efficiency Roll-Off

摘要

Organic light emitting diodes based on thermally activated delayed fluorescent(TADF) emitters with both high external quantum efficiency (EQE) andlow efficiency roll-off are under urgent pursuing. Three TADF emitters basedon fluorene-spiro-acridine derivatives as donors are developed. Composing ofrigid donor and acceptor, all emitters exhibit high PLQYs of 96–99. Directconjugation attached on acridine offers an enhanced reverse intersystemcrossing (k_(RISC)) in IA-TRZ, while the extension via spiro-junction acceleratesthe radiative decay rate (k_r) in 2S-TRZ and IT-TRZ. Remarkably, all emittersenable high electroluminescent performance with EQE of 35.6 for 2S-TRZ,36.1 for IT-TRZ and 32.0 for IA-TRZ, respectively, and very high luminanceof up to 100 000 cd m~(?2). Surprisingly, 2S-TRZ and IT-TRZ that hold larger k_rand smaller kRISC than that of IA-TRZ exhibit more relieved efficiency roll-off,indicating the significance of k_r. More importantly, IT-TRZ with a moderatek_r and k_(RISC) among these emitters shows the lowest roll-off which demonstratesthat the comprehensive consideration of all photophysical processesis important to attain excellent devices. It also emphasizes the molecularmodulation method through side group that can induce elaborate control ondecay channels for finely optimizing emitters. This study can provide a usefulperspective in designing practical emitters.