Highly Efficient Lead-Free (Bi,Ce)-Codoped Cs₂Ag_0.4Na_0.6InCl₆ Double Perovskites for White Light-Emitting Diodes

Lead-free double perovskite phosphors are promising alternatives to lead halide perovskites for wide uses in optoelectronic applications, but suffer from a low quantum efficiency. Here, we propose to enhance the quantum efficiency of orange-emitting Cs₂Ag_0.4Na_0.6InCl₆:Bi via a codoping strategy. The internal quantum efficiency of Cs₂Ag_0.4Na_0.6InCl₆:1% Bi phosphor was increased from 89.9% to the record 98.4 and 98.6% by codoping with 1% Ni and 1% Ce, respectively. High-level density functional theory calculations have revealed that the enhanced efficiency is ascribed to the formation of shallow trap states by codoping with Ce, while codoping with Mn can create delocalized deep traps that decrease the quantum efficiency. By applying the (Bi,Ce)-codoped sample together with a blue BaMgAl₁₀O₁₇:Eu²⁺ phosphor, a white light-emitting diode with an excellent color rendering index of 95.7 and a correlated color temperature of 4430 K has been demonstrated. The developed Cs₂Ag_0.4Na_0.6InCl₆:Bi,Ce phosphor shows a great potential as down-conversion luminescent material in solid-state lighting for general illumination.