Top-emitting organic light-emitting diodes: Influence of cavity design

We report on red top-emitting organic light-emitting diode structures with higher order cavities. The emission zone is placed in the first, second, and third antinodes of the electric field in the cavity by increasing the hole transport layer thickness. Furthermore, the thicknesses of the cathode and the capping layer are varied to achieve high efficiencies. Using doped charge transport layers and a phosphorescent emitter, we reach up to 29%, 17%, and 12% external quantum efficiencies for first, second, and third order devices, respectively. An optical model is further used to analyze the angular dependent emission.