Stable and Efficient Red Perovskite Light-Emitting Diodes Based on Ca²⁺-Doped CsPbI₃ Nanocrystals

α-CsPbI₃ nanocrystals (NCs) with poor stability prevent their wide applications in optoelectronic fields. Ca²⁺ (1.00 Å) as a new B-site doping ion can successfully boost CsPbI₃ NC performance with both improved phase stability and optoelectronic properties. With a Ca²⁺/Pb²⁺ ratio of 0.40%, both phase and photoluminescence (PL) stability could be greatly enhanced. Facilitated by increased tolerance factor, the cubic phase of its solid film could be maintained after 58 days in ambient condition or 4 h accelerated aging process at 120°C. The PL stability of its solution could be preserved to 83% after 147 days in ambient condition. Even using UV light to accelerate aging, the T₅₀ of PL could boost 1.8-folds as compared to CsPbI₃ NCs. Because Ca²⁺ doping can dramatically decrease defect densities of films and reduce hole injection barriers, the red light-emitting diodes (LEDs) exhibited about triple enhancement for maximum the external quantum efficiency (EQE) up to 7.8% and 2.2 times enhancement for half-lifetime of LED up to 85 min. We believe it is promising to further explore high-quality CsPbI₃ NC LEDs via a Ca²⁺-doping strategy.