High efficiency low color-temperature organic light-emitting diodes with a blend interlayer

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 similar to 2500 K with a similar to 15 lm W(-1) efficiency, and even as low as that of candles, which is similar to 2000 K with similar to 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.