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

(a) LED energy-level diagram, (b) current density, (c) luminescence, and (d) EQEs for LEDs; (e) EL spectra of Ca²⁺-doped CsPbI₃ NCs (0.40%) LEDs on various driving voltages and a photograph of the working device (inset in (e)); (f) operational stability of the LEDs at a constant current density of 5.0 mA/cm².