Efficient selenium-integrated TADF OLEDs with reduced roll-off

Organic light emitters based on multiresonance-induced thermally activated delayed fluorescent materials have great potential for realizing efficient, narrowband organic light-emitting diodes (OLEDs). However, at high brightness operation, efficiency roll-off attributed to the slow reverse intersystem crossing (RISC) process hinders the use of multiresonance-induced thermally activated delayed fluorescent materials in practical applications. Here we report a heavy-atom incorporating emitter, BNSeSe, which is based on a selenium-integrated boron-nitrogen skeleton and exhibits 100% photoluminescence quantum yield and a high RISC rate (k(RISC)) of 2.0 x 10(6) s(-1). The corresponding green OLEDs exhibit excellent external quantum efficiencies of up to 36.8% and ultra-low roll-off character at high brightnesses (with very small roll-off values of 2.8% and 14.9% at 1,000 cd m(-2) and 10,000 cd m(-2), respectively). Furthermore, the outstanding capability to harvest triplet excitons also enables BNSeSe to be a superior sensitizer for a hyperfluorescence OLED, which shows state-of-the-art performance with a high excellent external quantum efficiency of 40.5%, power efficiency beyond 200 lm W-1, and luminance close to 20,0000 cd m(-2). Green OLEDs based on BNSeSe offer high operational efficiency and reduced efficiency roll-off.