High Efficiency White and Colored Organic Electroluminescence

The need for light weight, low power multicolor displays and backlights has spurred interest in thin-film, organic electroluminescent (EL) devices. A typical organic EL device consists of an indium-tin oxide anode (ITO) layer on a glass substrate, and sequential layers of bis(triphenyl)diamine (TAD, hole transporter), tris(8-hydroxyquinoline)aluminum (A1Q, electron transporter and green light-emitter), and a low work function metal cathode (e.g., Al or Mg:Ag).1 Device efficiency, stability, and spectral output can be tailored by incorporating intermediate layers of organic hole-blockers2 or blue-emitters,3 or doping A1Q with narrow spectral linewidth organic dyes.4 Cavity resonance effects have been employed in lithographically patterned optical microcavities to select single5or multiple6 colors out of broad spectrum organic emitters like A1Q. Device efficiency is a critical parameter, especially for liquid crystal display backlight applications. We will describe an approach for white light EL and an approach for enhancing device efficiency.