Highly Efficient Organic Light-Emitting Devices for General Illumination

Lighting devices consume 8.3 percent of all energy produced in this country. Even a small improvement in lighting efficiency will save millions of barrels of oil or similar quantities of other fossil fuels used to produce electrical power. Organic light emitting devices have striking advantages for general-purpose illumination ¿ they are thin, flat, and lightweight, and also take up very little space. However, before they can become viable alternatives to conventional luminous sources, their energy efficiency, must be improved. Today, white organic light emitting devices have an efficiency of only 25-60 lumens per watt, while a lighting efficiency over 100 lumens per watt is needed for significant energy savings. One of the most significant factors responsible for their low efficiency is internal reflection at the interfaces between layers. To improve efficiency, this project will fabricate a random surface relief structure between the bases of organic light emitting devices and their active layers. The multilayer surface relief structure includes a polymer material with a high refractive index, matching that of the electroconductive anode, and a polymer with low refractive index. Light scattering at the interface between these layers will significantly improve the probability of photons penetrating through the interface. Phase I demonstrated that the light scattering by this relief enhances photons¿ probabilities of escaping, thus improving efficiency by factor of 1.5. In Phase II, a low-cost, roll-to-roll, mass production technology will be developed for fabricating flexible and rigid substrates, which will be fully compatible with subsequent organic light emitting device manufacturing. Commercial Applications and Other Benefits as described by the awardee: Flexible substrates for highly efficient organic light emitting devices should contribute to mass production, reduce costs, and make these devices more attractive to customers. All of these factors will result in energy savings and a reduced dependence on foreign oil.