Title: Enhanced light outcoupling from Organic Light Emitting Devices (OLEDs) for energy efficient solid state lighting (SSL) applications
Speaker: Eeshita Manna
Advisors: Drs. Joseph Shinar and Ruth Shinar
Abstract: SSL technology has the potential to contribute significantly to the world’s climate change issue by reducing energy usage and the carbon footprint as compared to other lighting technologies. Inorganic and Organic LEDs are preferable for many lighting applications. OLEDs are particularly suitable for lighting as they are potentially low cost, compatible with flexible substrates and provide warm and diffused light. However, there are many challenges that need to be resolved for integrating these devices as commercial products. One such challenge is light outcoupling. As only ~17-20% of generated photons escape to the forward hemisphere, enhancing light extraction can significantly contribute to the commercialization of OLEDs as SSL luminaires. Here, an enhancement in light outcoupling from bottom emitting OLEDs using a corrugated polycarbonate (PC) substrates is demonstrated along with a simple way to conformally develop multilayer PEDOT:PSS (poly(3,4 ethylenedioxythiophene) polystyrene sulfonate) anode on nano-patterned PC substrates. The effects of solution process parameters on conformal coating is discussed. Higher speed spin-coating for a longer duration is found to be helpful to grow thin PEDOT:PSS layers conformally on high plastic patterns demonstrating a uniform current distribution in multilayered anode yielding better devices. Several surface morphology and current distribution images of the PEDOT:PSS anode are shown to support the argument. Additionally at least 1.5 fold outcoupling enhancement from various OLEDs fabricated on PEDOT:PSS anode conformally coated on patterned PC substrates are demonstrated and the reproducibility and stability issues are discussed for these devices. Finally a potential solution to the problem to use a secondary semi-transparent anode along with PEDOT:PSS is proposed.