The investigation of light outcoupling in blue top-emitting OLEDs

A classic electromagnetic theory is used in this paper to investigate the light outcoupling in blue top-emitting organic light-emitting devices (TEOLEDs) with a samarium/silver (Sm/Ag) bilayer cathode. With the method, the outcoupling efficiency and the spectra of the devices with different top-electrodes and outcoupling layers were simulated. The calculated results demonstrate that in the devices, the increasing thickness of the Ag film would result in the redshift of blue emission and the decrease of emission intensity. While the thickness of the Sm film only influences the emission intensity of the devices. The thickness of the outcoupling layer is varied to obtain the saturated and efficient blue emission and then the optimal thickness is determined. The microcavity effect induced mainly by the bilayer cathode with a relatively high reflectivity is considered to explain the optical characteristics of the blue TEOLEDs, including some abnormal phenomena. The simulated results show good agreement with the measured data.