Very low color-temperature Organic Light-Emitting Diodes for lighting at night

Light sources with low color temperature (CT) are essential for their markedly less suppression effect on the secretion of melatonin, and high power efficiency is crucial for energy-saving. To provide visual comfort, the light source should also have a reasonably high color rendering index (CRI). In this report, we demonstrate the design and fabrication of low CT and high efficiency organic light-emitting diodes. The best resultant device exhibits a CT of 1,880 K, much lower than that of incandescent bulbs (2,000-2,500 K) and even as low as that of candles, (1,800-2,000 K), a beyond theoretical limit external quantum efficiency 22.7%, and 36.0 lm/W at 100 cd/m². 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.