Efficient solution-processed orange-red organic light-emitting diodes based on a novel thermally activated delayed fluorescence emitter

A novel thermally activated delayed fluorescence (TADF) emitter 1,2,3,4-tetrakis(3,6-di-tert-butyl-9H-carbazol-9-yl)thianthrene 5,5,10,10-tetraoxide (4t-BuCzTTR) was designed and synthesized for solution-processed red organic light-emitting diodes (OLEDs). With appropriate component segments and a well-arranged molecular structure, 4t-BuCzTTR successfully exhibits red fluorescence, significant TADF characteristics, excellent thermal stability and good solution processability. By using 4t-BuCzTTR as the emitter, the optimized doped OLED exhibits an orange-red emission with a peak at 592 nm and a high maximum external quantum efficiency of 6.2%. To the best of our knowledge, the result is not only higher than the theoretical limits of traditional fluorescent OLEDs, but also among the highest results of the reported solution-processed red OLEDs based on pure organic emitters, indicating the superiority of 4t-BuCzTTR.