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

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.