Low color-temperature, high color rendering index hybrid white organic light-emitting diodes by the effective control of exciton recombination zone

Abstract

Excitons dominate the optoelectronic properties of organic devices. Lighting sources with a low color-temperature (CT) and high color rendering index (CRI) are preferred for low suppression of melatonin secretion and better visual comfort. Herein, we designed and fabricated low CT and high CRI hybrid white organic light-emitting diodes (WOLEDs) via the effective control of exciton recombination in the emitting zone. In our structure, the three emissive layers of red EML/yellow-blue EML/spacer/green EML were employed, and the yellow phosphor was doped in the blue fluorescence host at a low concentration. This guaranteed that the yellow emission was from the phosphor, and the blue emission was from the fluorescent host; therefore, the four-color warm WOLEDs with low CT and high CRI were obtained well. Via optimization, it was observed that the best performing device showed a low CT of ∼1945 K with a maximum power efficiency of 20.6 lm W⁻¹ and retained ∼2000 K with a power efficiency of 16.9 lm W⁻¹ at a luminance of 1000 cd m⁻², which is better than other low CT light sources such as incandescent bulbs and candles. Furthermore, the resulting device also exhibited a CRI as high as 95. The low CT hybrid WOLEDs provide a promising alternative for night lighting to safeguard human health.