Highly efficient and nearly roll-off-free electrofluorescent devices via multiple sensitizations

The efficiency roll-off at high luminance has hindered the wide application of organic light-emitting diodes (OLEDs) for decades. To circumvent this issue, both high exciton utilization and short exciton residence should be satisfied, which, however, faces formidable challenges. Here, we propose an advanced approach of phosphor-assisted thermally activated delayed fluorophor (TADF)-sensitized fluorescence, abbreviated as TPSF. It is proved to be a rational strategy that can realize high quantum efficiency and elaborately accelerated radiative exciton consumption simultaneously by breaking singlet-triplet spin-flip cycles on a TADF host via multiple sensitizations. On the basis of a TADF molecule exhibiting anti-accumulation-caused quenching character, a proof-of-concept device exhibits a maximum external quantum efficiency (EQE_max) of 24.2% with an ultrahigh L_90% (the luminance at which EQE drops to 90% of its maximum value) of 190,500 cd m^-2 and a greatly improved operational stability, unlocking the full potential of OLEDs for ultrahigh-luminance applications.