Synergistic Regulation Effect of Nitrate and Calcium Ions for Highly Luminescent and Robust α-CsPbI Perovskite.

The α-CsPbI 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-CsPbI NCs is achieved through engineering the lattice symmetry of perovskite, enabled by the synergistic effect of NO ion passivation and Ca ion doping. The introduced NO ions enhance the phase-change energy barrier and the surface steric hindrance, thus promoting the formation of α-CsPbI NCs with hyper-symmetric crystal structure, while the Ca ion doping contributes to improving their lattice symmetry by significant regulation of the tolerance factor. As a result, the obtained α-CsPbI 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-CsPbI 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-CsPbI NCs based light-emitting-diode devices are constructed, exhibiting a power efficiency of 105.3 lm W and the excellent working stability for 18 h.