Ordered Phase Distribution of Quasi‐2D Perovskites Controlled by a Supramolecular Approach Enables Efficient Blue Light‐Emitting Diodes

Abstract Quasi‐2D perovskites demonstrate exceptional luminescent properties, mainly attributed to heightened radiative recombination facilitated by the energy transfer process among spontaneous quantum‐well structures featuring varied n‐value distributions. However, the rapid crystallization process often induces uncontrolled variations in phase composition, characterized by distinct “n” values, leading to suboptimal energy transfer efficiency. In this study, an innovative supramolecular strategy utilizing cryptand is introduced as an additive to regulate the phase distribution within quasi‐2D perovskite films. Cryptand effectively inhibited the aggregation of PEA⁺ and the formation of unsaturated Pb‐X coordination compounds, thereby suppressing the generation of low‐“n” phases. This intervention resulted in a continuous series of ordered intermediate phases with higher “n” values. The graded electronic structure facilitated efficient energy transfer from low‐“n” to high‐“n” phases, promoting effective radiation recombination. As a result, the optimized PeLEDs emitting at 490 nm demonstrated a remarkable external quantum efficiency (EQE) enhancement to 10.16%, compared to the reference device with an EQE of 2.33%. The device also exhibited impressive spectral and operational stability. The findings establish a viable strategy for precise phase distribution regulation in quasi‐2D perovskites, offering great potential for high‐performance blue PeLEDs.