Multifunctional Ionic-Ligand Regulated High-Quality γ-CsPbI3 Thin Films for Efficient and Bright Deep-Red Light-Emitting Diodes

Abstract

All-inorganic CsPbI₃ perovskite semiconductor is attractive for deep-red light-emitting diodes (LEDs) because of its high photoluminescence, good thermal stability, excellent charge transport, and solution processability. However, the metastable phase of optically active CsPbI₃ hinders the fabrication of efficient and bright deep-red LEDs. Herein, a multifunctional ionic ligand regulation strategy using (2-hydroxy-5-methylphenyl) triphenyl-phosphonium iodide and 3-(N, N-dimethyloctylammonio) propanesulfonate is reported to regulate the optically active CsPbI₃ crystallization and thus obtain high-quality γ-CsPbI₃ thin films. The high crystallinity and preferential orientation of γ-CsPbI₃ arise from the strong bonding between the ionic ligands and ionic lead halide clusters. The obtained γ-CsPbI₃ thin films also possess suppressed defect densities, high luminescence, and high stability. Using this high-quality thin film, an efficient and bright deep-red LED with a peak external quantum efficiency of 13.34% and a maximum luminance of 2110 cd m⁻² is successfully fabricated. The operational lifetime of the fabricated LED (time to half of the initial brightness, T₅₀) reaches up to 40 min under a high current density of 50 mA cm⁻² (corresponding to the initial brightness of 200 cd m⁻²).