Over 32.5% Efficient Top-Emitting Quantum-Dot LEDs with Angular-Independent Emission

Top-emitting quantum-dot light-emitting diodes (TQLEDs) with light emitted from the top semitransparent electrodes can improve the aperture ratio, efficiency, and color saturation of displays. However, because of the microcavity effect induced by the top semitransparent electrodes, the devices usually exhibit angular-dependent emission, which is unfavorable for display applications. In this study, highly transparent and conductive indium zinc oxide (IZO) is used as the top electrode to reduce the microcavity effect, thereby improving the angular color stability. By further applying a nanosphere scattering layer on the IZO top electrode, the trapped light is greatly extracted, and thus, the external quantum efficiencies (EQEs) are remarkably improved by 35, 50, and 133% for the red, green, and blue devices, respectively. The champion red TQLEDs exhibit a record EQE of 32.5% with angular-independent color emission. The demonstrated TQLEDs with high efficiency, high color stability, and a high aperture ratio could be the ideal candidates for QLED displays.