Ultra-low power-consumption OLEDs via phosphor-assisted thermally-activated-delayed-fluorescence-sensitized narrowband emission

The further success of OLED beyond conventional low-luminance display applications has been hampered by the low power efficiency (PE) at high luminance. Here, we demonstrate the strategic implementation of an exceptionally high-PE, high-luminance OLED using a phosphor-assisted thermally-activated-delayed-fluorescence (TADF)-sensitized narrowband emission. On the basis of a TADF sensitizing-host possessing a fast reverse intersystem crossing, an anti-aggregation-caused-quenching character and a good bipolar charge-transporting ability, this design achieves not only a 100% exciton radiative consumption with decay times mainly in the sub-microsecond regime to mitigate exciton annihilations for nearly roll-off-free external quantum efficiency, but also narrowband emission with both small energetic loss during energy transfer and resistive loss with increasing luminance. Consequently, besides a maximum PE of 187.7 lm/W, an exceptionally high critical maximum luminance (where a PE of 100 lm/W is maintained) of over 110,000 cd/m2 is achieved for the proof-of-the-concept device, nearly one-of-magnitude higher than the previous record. The device performance of organic light-emitting diodes has been hampered by the low power efficiency at high luminance. Here, authors employ a thermally activated delayed fluorescence sensitizing host, achieving maximum power efficiency close to 190 lm/W and maximum luminance of over 110,000 cd/m2.