Chemical Reaction Modulated Low‐Dimensional Phase Toward Highly Efficient Sky‐Blue Perovskite Light‐Emitting Diodes

Blue perovskite light‐emitting diodes (PeLEDs) are crucial avenues for achieving full‐color displays and lighting based on perovskite materials. However, the relatively low external quantum efficiency (EQE) has hindered their progression towards commercial applications. Quasi‐two‐dimensional (quasi‐2D) perovskites stand out as promising candidates for blue PeLEDs, with optimized control over low‐dimensional phases contributing to enhanced radiative properties of excitons. Herein, the impact of organic molecular dopants on the crystallization of various n‐phase structures in quasi‐2D perovskite films. The results reveal that the highly reactive bis(4‐(trifluoromethyl)phenyl)phosphine oxide (BTF‐PPO) molecule could effectively restrain the formation of organic spacer cation‐ordered layered perovskite phases through chemical reactions, simultaneously passivate those uncoordinated Pb2+ defects. Consequently, the prepared PeLEDs exhibited a maximum EQE of 16.6% (@ 490 nm). The finding provides a new route to design dopant molecules for phase modulation in quasi‐2D PeLEDs.