Cu+ doping enhances self-trapped exciton emission in alloyed Cs2(Ag/Na)InCl6 double perovskite

All-inorganic 3D lead-free double perovskites (DPs) with broadband self-trapped exciton (STE) emission have shown great promise as alternatives to lead halide perovskites in various optoelectronic applications such as light-emitting diodes (LEDs) and photodetectors. A fundamental understanding of the effect of doping on the optical properties of DPs, especially the STE dynamics, is of vital importance for their performance optimization and applications.

In a study published in Advanced Science, the research group led by Prof. Chen Xueyuan from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences developed a unique strategy via Cu⁺ doping to achieve efficient STE emission in the alloyed lead-free Cs₂(Ag/Na)InCl₆ DP crystals.

This unique strategy based on Cu⁺ doping boosts the STE emission in the alloyed Cs₂(Ag/Na)InCl₆ DPs. The researchers used a small amount (1.0 mol%) of Cu⁺ doping to realize the boosted STE emission in the crystals, with photoluminescence (PL) quantum yield increasing from 19.0% to 62.6% and excitation band shifting from 310 nm to 365 nm.

They comprehensively surveyed the effect of Cu⁺ doping on the electronic structure and optical properties of Cs₂(Ag/Na)InCl₆ and the STE dynamics. The as-synthesized Cs₂(Ag/Na)InCl₆: Cu⁺ crystals exhibit significantly enhanced PL stemming from the increased radiative recombination rate of STEs as well as the improved STE density.

By means of temperature-dependent PL and ultrafast femtosecond transient absorption spectroscopies, the researchers unraveled that the remarkable PL enhancement was ascribed to the increased density and radiative recombination rate of STEs, as a result of symmetry breakdown of the STE wavefunction at the octahedral Ag⁺ site induced by Cu⁺ doping.

Besides, the researchers demonstrated the excellent air, structural and thermal stability of these Cu⁺-doped Cs₂(Ag/Na)InCl₆ crystals, and revealed their great potentials as efficient yellow-emitting phosphors for application in near-ultraviolet (NUV)-converted white LEDs.

This study provides deep insights into the STE dynamics in Cu⁺-doped Cs₂(Ag/Na)InCl₆, thereby laying a foundation for future design of new lead-free DPs with efficient STE emission.