Abstract
Low color temperature (CT) lighting sources are crucial for their low suppression of melatonin secretion, and high power efficiency is essential for energy-saving. This study demonstrates the incorporation of a blend interlayer between emissive layers to improve the device performance of low CT organic light emitting diodes. The resulting devices exhibit a CT much lower than that of incandescent bulbs, which is ∼2500 K with a ∼15 lm W -1 efficiency, and even as low as that of candles, which is ∼2000 K with ∼0.1 lm W -1 . The best device fabricated shows an external quantum efficiency of 22.7% and 36 lm W -1 (54 cd A -1 ) with 1880 K at 100 cd m -2 , or 20.8% and 29 lm W -1 (50 cd A -1 ) with 1940 K at 1000 cd m -2 . The high efficiency of the proposed device may be attributed to its interlayer, which helps effectively distribute the entering carriers into the available recombination zones. © 2011 The Royal Society of Chemistry.