Manipulating Crystallization Dynamics for Efficient and Spectrally Stable Blue Perovskite Light‐Emitting Diodes

Reduced‐dimensional perovskite light‐emitting diodes (PeLEDs) have shown great potential in solution‐processed high‐definition displays. However, the inferior electroluminescent (EL) performance of blue PeLEDs has become a huge challenge for their commercialization. The inefficient domain control [number of PbX6− layers (n)] and deleterious phase segregation make the blue PeLEDs suffer from low EL efficiency and poor spectral stability. Here, a rational strategy for perovskite crystallization control by adjusting the precursor concentration is proposed for improving phase distribution and suppressing ion migration in reduced‐dimensional mixed‐halide blue perovskite films. Based on this method, efficient sky‐blue PeLEDs exhibit a maximum external quantum efficiency (EQE) of 8.5% with stable EL spectra at 482 nm. Additionally, spectrally stable pure‐blue PeLEDs at 474 and 468 nm are further obtained with maximum EQEs of 4.0% and 2.4%, respectively. These findings may provide an alternative scheme for manipulating perovskite crystallization dynamics toward efficient and stable PeLEDs. A rational crystallization manipulation scheme for achieving controlled phase distribution and suppressed halide ion migration is proposed by means of delicate precursor dilution. Consequently, spectrally stable blue perovskite light‐emitting diodes with significantly improved electroluminescent efficiency have been obtained, displaying a high external quantum efficiency of 8.5% at 482 nm.