Angle-Independent Top-Emitting Quantum-Dot Light-Emitting Diodes Using a Solution-Processed Subwavelength Scattering–Capping Layer

Owing to the excellent optoelectronic properties of colloidal quantum dots (QDs), light-emitting diodes based on QDs (QLEDs) have been considered one of the most promising electroluminescence (EL) devices for full-color displays with a wide color gamut. Particularly, top-emission device architecture has been of interest to both academia and industry, because of the advantages in light outcoupling, aperture ratios, and integration with conventional backplanes. In this structure, however, angle-dependent color shifts originating from a variation in microcavity length are a critical issue that needs to be resolved. Here, a solution-processed dual-functional scattering–capping layer (SCPL) using ZnO nanoparticles on top-emitting QLEDs with ZnSeTe/ZnSe/ZnS QDs to modulate the optical interference is presented. By precisely controlling the thickness of the SCPL, the EL intensity and spectrum can be redistributed to produce a uniform color from any viewing angle. It is discovered that, unlike conventional CPLs, the formation of random nanocracks and nanoclusters in the SCPL adds subwavelength light-scattering capabilities, which promotes light extraction. The QLEDs with the solution-processed SCPL exhibit a 44% increase in the maximum external quantum efficiency, with completely imperceptible angle-dependent spectral shifts. The SCPL is expected to be applied to the development of high-performance and next-generation QLED displays.