Quasi‐2D perovskite light‐emitting diodes (PeLEDs) are promising candidates to realize superior luminescent. However, the poorly controlled phase distribution and surface defects hinder the improvement of the device's performance. Here, by introducing rubidium bromide (RbBr) to tune the crystallization kinetics of quasi‐2D perovskites, more uniform phase distribution is achieved through the suppression of medium‐n phases, resulting in narrower emission spectrum and more efficient energy transfer. Meanwhile, the defects are effectively passivated by the addition of RbBr. As a result, the photoluminescence quantum yield (PLQY) of quasi‐2D perovskite films increases significantly from 45.6% to 81.3%, and the maximum external quantum efficiency (EQE) of PeLEDs reaches 18.92%. This finding provides a new insight into the phase distribution control of quasi‐2D perovskites and the further improvement of PeLEDs.

Perovskite quantum dot light-emitting diodes (QLEDs) with high color purity and wide color gamut have good application prospects in the next generation of display technology. However, colloidal perovskite quantum dots (PQDs) may introduce a large number of defects during the film-forming process, which is not conducive to the luminous efficiency of the device. Meanwhile, the disordered film formation of PQDs will form interfacial defects and reduce the device performance. Here, we report an interface-induced crystallinity enhancement (IICE) strategy to increase the crystallinity of PQDs at the hole transport layer (HTL)/PQD interface. As a result, both the Br − vacancies in the PQD film and the interfacial defects were well passivated and the leakage current was also suppressed. We achieved QLEDs with a maximum external quantum efficiency (EQE) of 16.45% and current efficiency (CE) of 61.77 cd/A, showing improved performance to more than twice that of the control devices. The IICE strategy paves a new way to enhance the crystallinity of PQD films, so as to improve the performance of QLEDs for application in the future display field.