Synergistic Regulation Effect of Nitrate and Calcium Ions for Highly Luminescent and Robust α-CsPbI 3 Perovskite.

The α-CsPbI ₃ 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 ₃ NCs is achieved through engineering the lattice symmetry of perovskite, enabled by the synergistic effect of NO ₃ ^- ion passivation and Ca ²⁺ ion doping. The introduced NO ₃ ^- ions enhance the phase-change energy barrier and the surface steric hindrance, thus promoting the formation of α-CsPbI ₃ NCs with hyper-symmetric crystal structure, while the Ca ²⁺ ion doping contributes to improving their lattice symmetry by significant regulation of the tolerance factor. As a result, the obtained α-CsPbI ₃ 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 ₃ 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 ₃ 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.
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