Synergistic Regulation Effect of Nitrate and Calcium Ions for Highly Luminescent and Robust α‐CsPbI₃ Perovskite

Abstract The α‐CsPbI₃ nanocrystals (NCs) easily transform into yellow non‐perovskite, accompanying with declining photoelectric properties that restricting their practical applications in diverse fields. Herein, the highly luminescent and robust α‐CsPbI₃ NCs is achieved through engineering the lattice symmetry of perovskite, enabled by the synergistic effect of NO₃⁻ ion passivation and Ca²⁺ ion doping. The introduced NO₃⁻ ions enhance the phase‐change energy barrier and the surface steric hindrance, thus promoting the formation of α‐CsPbI₃ NCs with hyper‐symmetric crystal structure, while the Ca²⁺ ion doping contributes to improving their lattice symmetry by significant regulation of the tolerance factor. As a result, the obtained α‐CsPbI₃ NCs display an outstanding photoluminescence quantum yield of 96.6%, together with the reduced defect state density and eminent conductivity. Most importantly, the as‐engineered α‐CsPbI₃ NCs exhibit excellent stability under ambient conditions for 9 months and UV illumination for 32 h. It displays brilliant thermal stability, maintaining luminous intensity for 15 min under 140 °C, and performing desired durability and reversibility, evidenced by 160 °C cyclic test and 120 °C reversibility test. Given enhanced robustness, the as‐engineered α‐CsPbI₃ NCs based light‐emitting‐diode devices are constructed, exhibiting a power efficiency of 105.3 lm W⁻¹ and the excellent working stability for 18 h.