Eastern Kodak Company

Lighting consumes more than 20% of electricity generated in the United States. Solid state lighting relies upon either inorganic or organic light-emitting diodes (OLEDs). OLED devices because of their thinness, fast response, excellent color, and efficiency could become the technology of choice for future lighting applications, provided progress is made to increase power efficiency and device lifetime and to develop cost-effective manufacturing processes. As a first step in this process, Eastman Kodak Company has demonstrated an OLED device architecture having an efficacy over 50 lm/W that exceeds the specifications of DOE Energy Star Program Requirements for Solid State Lighting. The project included work designed to optimize an OLED device, based on a stacked-OLED structure, with performance parameters of: low voltage; improved light extraction efficiency; improved internal quantum efficiency; and acceptable lifetime. The stated goal for the end of the project was delivery of an OLED device architecture, suitable for development into successful commercial products, having over 50 lum/W power efficiency and 10,000 hours lifetime at 1000 cd/m{sup 2}. During the project, Kodak developed and tested a tandem hybrid IES device made with a fluorescent blue emitter, a phosphorescent yellow emitter, and a phosphorescent red emitter in a stacked structure. The challenge was to find low voltage materials that do not absorb excessive amounts of emitted light when the extraction enhancement structure is applied. Because an extraction enhancement structure forces the emitted light to travel several times through the OLED layers before it is emitted, it exacerbates the absorption loss. A variety of ETL and HTL materials was investigated for application in the low voltage SSL device structure. Several of the materials were found to successfully yield low operating device voltages without incurring excessive absorption loss when the extraction enhancement structure was applied. An internal extraction layer comprises two essential components: a light extraction element (LEE) that does the actual extraction of emitted light and a light coupling layer (LCL) that allows the emitted light to interact with the extraction element. Modeling results show that the optical index of the LCL needs to be high, preferably higher than that of the organic layers with an n value of {approx}1.8. In addition, since the OLED structure needs to be built on top of it the LCL needs to be physically and chemically benign. As the project concluded, our focus was on the tandem hybrid device, which proved to be the more efficient architecture. Cost-efficient device fabrication will provide the next challenges with this device architecture in order to allow this architecture to be commercialized