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/m<sup>2</sup>. 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 SPIE

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