Nano-Structures Enabling Sunlight and Candlelight-Style OLEDs
Nano structures enable organic light-emitting diode (OLED) devices to be fabricated with relatively high efficiency and brightness, opening up a new era for high quality displays and lighting, wherein devising a pseudo-natural light is always a must. The uses of incandescent bulbs are the most friendly, electricity-driven lighting sources, lighting measure from the perspectives of human eye protection, melatonin generation, artifacts, ecosystems, the environment, and the night skies due to their intrinsically low blue emission. However, they are phasing out because of the energy wasting. To overcome these difficulties, researchers are focusing on developing a new light with high efficiency, whose emission spectra would also match with those of the natural lights. In 2009, Jou’s group invented the world’s first electrically powered sunlight-style OLED that yielded a sunlight-style illumination with various daylight chromaticities, whose color temperature ranges between 2,300 and 8,200 K, fully covering those of the entire daylight at different times and regions, and contributed a noteworthy incentive to OLED technology in general lighting. By putting more efforts on this technology, a blue hazard free, low color temperature candlelight-style OLED was developed by employing candlelight complementary emitters, namely orange-red, yellow, green, and sky-blue. The resultant candlelight OLED that exhibits a 1,900 K color temperature is exactly like candles or oil lamps, which is friendly to human eyes, physiologies, ecosystems, artifacts, and night-skies. Specifically, it is at least 10 times safer from the retina protection perspective or 5 times better for melatonin to naturally occur after dusk, as compared with the blue light-enriched white OLED, LED and CFL counterparts. In this article, we discuss the device structure, physics, and engineering behind the serendipity of the pseudo-natural light-style OLEDs.