Efficient and Stable Blue Perovskite Light‐Emitting Diodes Enabled by Effective Hydrolysis of Dichloride

Abstract Despite the substantial progress in sky‐blue (480−495 nm) perovskite light‐emitting diodes (PeLEDs), the pure‐blue PeLEDs (<480 nm) merely show moderate performances. As a straightforward and effective facile way to obtain pure‐blue emission, the bromide‐chloride mixed perovskites have received considerable attention. However, the tricky issue of halide migration in the mixed halide perovskites makes a tough challenge to achieve efficient PeLEDs with stable electroluminescence (EL) spectra. Herein, the in situ treatment of Cl‐rich benzene phosphorus oxydichloride (BPOD) is proposed to achieve high‐quality pure‐blue perovskites by simultaneously enlarging the perovskite bandgap, passivating the halide vacancy defects, and immobilizing the halide ions through the hydrolysis products of chloride ions and phenylphosphonic acid. As a result, highly‐performed pure‐blue PeLEDs with a maximum external quantum efficiency (EQE) of 9.3% at 477 nm, an impressive lifetime of 34.7 min at 104 cd m −2 , and very stable EL spectra are achieved, which are superior to the conventional mixed halide PeLEDs based on lead‐chloride precursor, representing one of the best performances for mixed halide pure‐blue PeLEDs. Therefore, this work contributes a feasible and effective method for efficient and stable pure‐blue PeLEDs.