Significant LED performance improvements have been achieved by taking advantage of novel materials. An organic light emitting diode (OLED) requires at least one transparent electrode, which is most commonly indium tin oxide (ITO). While ITO is both transparent and a good electrical conductor, its light transmission differs from the other organic material layers used in the device, leading to internal reflections which reduce efficiency. Researchers replaced ITO with a special highly conductive polymer known as PEDOT:PSS. The new OLEDs have a peak power efficiency and other key properties that are among the highest reported to date. They are 44% more efficient than comparable devices made with ITO. The researchers used computer simulations to show that the enhanced performance is largely an effect of the difference of optical properties between the polymer-based electrode and ITO. Because of the improved efficiency and potentially easier processing of these ITO-free OLEDs, the results pave the way for improved commercial OLEDs at lower cost.
- Min Cai, Zhou Ye, Teng Xiao, Rui Liu, Ying Chen, Robert W. Mayer, Rana Biswas, Kai-Ming Ho, Ruth Shinar, and Joseph Shinar. Extremely Efficient Indium-Tin-Oxide-Free Green Phosphorescent Organic Light-Emitting Diodes. Advanced Materials, 2012, 24, 4337-4342. DOI:10.1002/adma.201202035