High efficiency color-tunable organic light-emitting diodes with ultra-thin emissive layers in blue phosphor doped exciplex

High efficiency color-tunable organic light-emitting diodes (CT-OLEDs) have been demonstrated by combining non-doped ultra-thin red and green phosphorescent emitters with a blue phosphorescence-doped exciplex system. The resultant devices deliver a sunlight-style emission with a wide correlated color-temperature span from 2143 to 7563 K and achieve the maximum current efficiency, the power efficiency, and the external quantum efficiency of 34.4 cd A−1, 39.5 lm W−1, and 18.6%, respectively, without any out-coupling enhancements. Furthermore, the CT-OLEDs exhibit low efficiency roll-off that the external quantum efficiencies still remain 18.5% and 17.1% even at 1000 and 5000 cd m−2, respectively, which are more efficient than those of state-of-the-art CT-OLEDs.