Highly Stable Mixed Halide Perovskite Nanocrystals for High Performance Pure‐Red Light‐Emitting Diodes

Abstract Pure‐red CsPbBr x I 3−x nanocrystals (NCs) light‐emitting diodes (PeLEDs) are promising candidates for high‐performance display due to their high brightness, excellent color purity and readily tunable band gap. However, achieving highly stable pure‐red PeLEDs is still challenging due to phase segregation in the mixed halide CsPbBr x I 3−x NCs. Herein, pure‐red mixed halide CsPbBr x I 3−x NCs with a relatively small size are synthesized using phosphate acid as a ligand, effectively avoiding spontaneous phase separation. The strong interaction between phosphate ligands and Pb 2+ facilitates the slow formation of CsPbBr x I 3−x NCs, resulting in relatively small NC sizes. In addition, a dense phosphate passivation layer forms around the surface of NCs, which imparts excellent stability to the NCs against light, moisture and heat treatment. Utilizing the highly stable CsPbBr x I 3−x NCs as an emission layer, pure‐red PeLEDs emitting at 633 nm, with an external quantum efficiency (EQE) of 10.0%, a brightness of 8231 cd m −2 and a half‐life of 393 min, are fabricated. Notably, the PeLEDs show excellent stability, with negligible changes in the emission spectra under an elevated bias voltage of 14 V. This work provides a new avenue for enhancing the performance of pure red PeLEDs through strongly coordinated phosphate ligand passivation.