Cu+ Doping Enhances Self-trapped Exciton Emission in Alloyed Cs2(Ag/Na)InCl6 Double Perovskite----Chinese Academy of Sciences

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Cu⁺ Doping Enhances Self-trapped Exciton Emission in Alloyed Cs₂(Ag/Na)InCl₆ Double Perovskite

Mar 28, 2022

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. Fundamental understanding 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.