Top-emitting white organic light-emitting diodes based on a ZnS light outcoupling layer

Abstract

Top-emitting white organic light-emitting diode (TEWOLED) has potential applications in lighting and full color displays. Microcavity effect in TEWOLED restrains the realization of the white emission with excellent optical and electric performances. In this paper, a ZnS film with a high refractive index used as a light outcoupling layer is introduced into the metal cathode to enhance its transmittivity to a maximal value in the blue light wavelength region. In addition, transfer matrix theory is utilized to optimize the thicknesses of the cathode and the ZnS outcoupling layer and the wide-angle interference is used to design the position of the blue emission layer inside the organic light-emitting diode. Based on the above work, the white light with relatively high luminous efficiency, good color purity, and small CIE coordinate change is acquired. The corresponding luminance and current efficicency are 9213 cd/m2 and 3 cd/A, respectively. The CIE coordinates belong to the white emission and are near the white light equal-energy point. The white emission also shows stable spectra with respect to the observation angle, with a limited CIE coordinate change of (0.02, 0) for a large observation angle change from 0 to 60.