Optical processes of organic emitters in optical microcavity - art. no. 663907

Optical characteristics of microcavity organic light-emitting devices (OLEDs) having two mirrors are examined. Analyses show that a high-reflection back mirror and a low-loss high-reflection exit mirror are essential for such microcavity devices to obtain luminance enhancement relative to conventional noncavity devices. The capping layer in the composite mirror plays the role of enhancing reflection and reducing absorption loss, rather than enhancing transmission. In addition, by setting the normal-direction resonant wavelength around the peak wavelength of the intrinsic emission, one obtains the highest luminance enhancement along the normal direction and hardly detectable color shift with viewing angles, yet accompanied by highly directed emission and lower external quantum efficiency. On the other hand, the highest enhancement in external quantum efficiencies and the most uniform brightness distribution are obtained by setting the normal-direction resonant wavelength 20-40 nm longer than the peak wavelength of the intrinsic emission, yet with noticeable color shift over viewing angles. Due to the tradeoffs between different emission characteristics in choosing the resonant wavelength, the exact design of microcavity devices would depend on actual applications.