Light Out-coupling Efficiency Enhancement in Organic Light-emitting Diodes Using a Multilayer Stacked Electrode with Sol-gel Processed TaO

We demonstrate enhanced light out-coupling efficiency of organic light-emitting diodes by applying a multilayer stacked electrode structure consisting of fast and cost-effective sol-gel processed tantalum pentoxide (TaO), thin layer of Au and molybdenum trioxide (MoO). The application of the TaO/Au/MoO electrode can modulate the optical characteristics of the device due to the optical microcavity effect. The refractive index of the sol-gel processed TaO thin film varied depending on the annealing temperature and reached a maximum at 400 °C (n = 2.2 at 512 nm). The influence of the refractive index of the TaO layer and the thickness of the multilayer electrode stack on the optical microcavity effect was systematically investigated. The device with the TaO/Au/MoO electrode, fabricated at an optimum condition based on the simulation result by calculating the photon flux, exhibited 52% enhancement in light out-coupling efficiency at 1000 cd/m and improved color stability with the viewing angle, having near-Lambertian emission.