Highly efficient color-temperature tunable organic light-emitting diodes

Color temperature (CT) is crucial to human physiology. A simple organic light-emitting diode with CT tunable between 1700 and 5200 K and a high current efficiency of 23.7 cd A(-1) at 1000 cd m(-2) is demonstrated. The wide CT span may be attributed to the use of a hole-modulation material with high triplet energy and high electron mobility, and the high efficiency to the use of emitters with high quantum yield. The efficiency is further improved to 31.3 cd A(-1) by using double hole-modulation layers, which can more effectively prevent excessive hole-injection, leading to a better carrier-injection balance.