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

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.