High Efficiency Ultra‐Narrow Emission Quantum Dot Light‐Emitting Diodes Enabled by Microcavity

A wide‐color‐gamut display enableby a narrow emission linewidth facilitates a visually immersive experience akin to the real world. Quantum dot light‐emitting diodes (QLEDs) with excellent color purity and high efficiency hold great promise as future candidates for high‐definition displays. However, most devices typically exhibit emission linewidths exceeding 20 nm, and lack a universal strategy for further enhancing the color purity. In this study, a planar microcavity structure for realizing ultra‐narrow emissions is developed by incorporating a distributed Bragg reflector into normal electroluminescent devices. By leveraging the strong optical resonance effect derived from this microcavity structure, red QLEDs are successfully fabricated with an extraordinary full width at half maximum of 11 nm in the normal direction, beyond the BT.2020 color coordinates. The fabricated red‐microcavity QLEDs exhibit a considerable enhancement in the external quantum efficiency, which increases from 28.2% to 35.6%, together with an extended operating lifetime. The strategy adopted herein will serve as an effective reference for achieving ultra‐narrow emission and high‐efficiency QLEDs. Ultra‐high color purity and efficient forward‐emitting red quantum dot light‐emitting diodes (QLEDs) with an emission linewidth of 11 nm and an a external quantum efficiency (EQE) of 35.6% are achieved by integrating distributed Bragg reflector into normal electroluminescent (EL) devices to form a microcavity. This study fills the gap of EL linewidth near 10 nm for red QLEDs with EQE exceeding 20% and significantly promotes the commercialization for ultra‐high‐definition display applications.