Partially Ionized Amino Acid Salt Enabling Spatially Vertical n‐Phase Distribution of Quasi‐2D Perovskite for Efficient Deep‐Blue Light‐Emitting Diodes

The deep‐blue perovskite light‐emitting diodes (PeLEDs) are of essential and indispensable for the application in full‐gamut display. However, the deep blue emission required large bandgap in small n phase exhibits high surface activity that gives rise to the difficulty of n phase distribution control spatially and proportionally in quasi‐2D perovskite films. Here, the deep‐blue pure‐bromide perovskite films is present that exhibit spatially vertical n phase distribution, owing to the partially ionized amino acid salt of 3‐Ammonium propionic acid bromide (3CBr) modulated crystallization kinetic of perovskite. The strong interaction of 3CBr and perovskite lattice improves the stability of small n phases, showing tunable photoluminescence (PL) emission and enhanced PL quantum yield (PLQY). The achieved champion deep blue PeLED shows a maximum EQE of 3.64% at electroluminescence (EL) emission wavelength of 466 nm, locating at the top rank of the similar devices. This work provides an effective strategy to fabricating efficient deep‐blue perovskite films and devices, promoting the development of perovskite‐based application in display. The strong interaction of 3CBr and perovskite enables crystallization kinetic control for small n phases, leading to the improved stability, PLQY, and the vertical n phase distribution in the deep‐blue perovskite film. The achieved champion deep blue PeLED show a maximum EQE of 3.64% at EL emission wavelength of 466 nm.