Quantum‐Well Encapsulation Enabling Air‐Processed Quasi‐2D Perovskites with Long‐Term Stability for Large‐Area Deep‐Blue Light‐Emitting Diodes

Pure‐bromide quasi‐2D perovskites have achieved notable progress in enabling air‐processed light‐emitting diodes (PeLEDs). However, the ultrathin quantum well emitters are characteristic of high surface activity, leading to the deep‐blue pure‐bromide quasi‐2D perovskite films still face challenges of long‐term stability and optical tunability in ambient conditions. Here, a hydrolysis strategy is presented for achieving quantum well encapsulation, which enables significant enhancement in the stability and optical tunability of blue perovskite films, due to the hydrolysis of AlBr 3 or SiBr 4 generating oxo‐bridged networks that passivate the surfaces of the quantum wells. The air‐processed blue films exhibit an outstanding photoluminescence quantum yield of ≈50.9%, and remarkable color‐stable‐emission even after exposing in air (RH ≈10–20%, room temperature) for 2160 h, or under thermal stimuli (70 °C) for 92 h, which exceptionally exceeds the long‐term stability of similar films fabricated in an inert environment. The deep‐blue PeLEDs achieve a record external quantum efficiency of 4.02% for air‐processed blue devices, which is comparable to the performance of analogous devices fabricated in a glove box. Notably, large‐area deep‐blue PeLEDs with an emission area of 9.0 cm 2 are presented, providing a promising path toward the development of high‐performance, commercially viable perovskite display technologies.