Nondestructive halide exchange via S_N2-like mechanism for efficient blue perovskite light-emitting diodes

Blue perovskite light-emitting diodes (PeLEDs) still remain poorly developed due to the big challenge of achieving high-quality mixed-halide perovskites with wide optical bandgaps. Halide exchange is an effective scheme to tune the emission color of PeLEDs, while making perovskites susceptible to high defect density due to solvent erosion. Herein, we propose a versatile strategy for nondestructive in-situ halide exchange to obtain high-quality blue perovskites with low trap density and tunable bandgaps through long alkyl chain chloride incorporated chloroform post-treatment. In comparison with conventional halide exchange method, the ionic exchange mechanism of the present strategy is similar to a bimolecular nucleophilic substitution process, which simultaneously modulates perovskite bandgaps and inhibits new halogen vacancy generation. Consequently, efficient PeLEDs across blue spectral regions are obtained, exhibiting external quantum efficiencies of 23.6% (sky-blue emission at 488 nm), 20.9% (pure-blue emission at 478 nm), and 15.0% (deep-blue emission at 468 nm), respectively.