Highly Efficient Light‐Emitting Diodes Based on Self‐Assembled Colloidal Quantum Wells

Nanocrystal‐based light‐emitting diodes (Nc‐LEDs) have immense potential for next‐generation high‐definition displays and lighting applications. They offer numerous advantages, such as low cost, high luminous efficiency, narrow emission, and long lifetime. However, the external quantum efficiency (EQE) of Nc‐LEDs, typically employing isotropic nanocrystals, is limited by the out‐coupling factor. Here efficient, bright, and long lifetime red Nc‐LEDs based on anisotropic nanocrystals of colloidal quantum wells (CQWs) are demonstrated. Through modification of the substrate's surface properties and control of the interactions among CQWs, a self‐assembled layer with an exceptionally high distribution of in‐plane transitions dipole moment of 95%, resulting in an out‐coupling factor of 37% is successfully spin‐coated. The devices exhibit a remarkable peak EQE of 26.9%, accompanied by a maximum brightness of 55 754 cd m−2 and a long operational lifetime (T95@100 cd m−2) over 15 000 h. These achievements represent a significant advancement compared to previous studies on Nc‐LEDs incorporating anisotropic nanocrystals. The work is expected to provide a general self‐assembly strategy for enhancing the light extraction efficiency of Nc‐LEDs based on anisotropic nanocrystals. Through modification of the substrate's surface properties and control of the interactions among colloidal quantum wells, self‐assembled of the layer with an exceptionally high distribution of in‐plane transitions dipole moment of 95% is successfully realized. Incorporation of the novel hole transfer layer PF8Cz effectively suppresses electron leakage, which leads to the high‐performance light‐emitting diodes with a peak external quantum efficiency of 26.9%.