This structure for organic light emitting diodes (OLEDs) includes a layer of low refractive index material that enhances the light outcoupling in a bottom-emitting OLED. OLEDs are used in mobile devices and computer displays, wearable electronics and televisions due to their wide spectrum of colors, fast response time, flexibility, and low-processing cost. Increasing demands for cheaper and more energy-efficient consumer electronics suggests revenue upwards of $20 billion by 2020 for greener phosphorescent lighting sources. Traditional layering structure in OLEDs allows less than 30 percent of the light generated to escape the device and become useful, which is defined as “outcoupling efficiency.” Researchers at the University of Florida have inserted a layer of low refractive index material, a corrugated substrate, and a macrolens that can significantly enhance the light outcoupling in a bottom-emitting OLED, producing a corrugated green phosphorescent OLED with an external quantum efficiency of 67 percent.
Low refractive index layer for more light-efficient OLEDs
This low refractive index layer inserted between the bottom transparent electrode and the corrugated substrate enhances the light outcoupling in a bottom-emitting OLED. Traditionally, a bottom-emitting OLED comprises a glass substrate, a transparent bottom electrode, organic layer stacks and a reflective top electrode and loses 70 percent or more of the light generated even if the internal quantum efficiency is 100 percent. This OLED structure with the enhanced refractive index contrast, corrugated substrate and macrolens extracts trapped light, increasing outcoupling significantly, producing a high current efficiency of 201 cd/A and a high external quantum efficiency of 67 percent.