Ultra-stable blue-emitting lead-free double perovskite Cs₂SnCl₆ nanocrystals enabled by an aqueous synthesis on a microfluidic platform

Blue emitting Sn-based lead-free halide perovskite nanocrystals (NCs) are considered to be a promising material in lighting and displays. However, industrialised fabrication of blue-emitting NCs still remains a significant challenge due to the use of toxic solvents and optical instability, not mentioning in large-scale synthesis. In this work, a green-route synthesis of blue-emitting lead-free halide perovskite Cs₂SnCl₆ powders is developed, in which deionized water with a small amount of inorganic acid is used as the solvent and the synthesis of the Cs₂SnCl₆ powders is achieved on a microfluidic platform. Using the Cs₂SnCl₆ powders, we prepare Cs₂SnCl₆ NCs via an ultrasonication process. Changing the volume ratio of the ligands (oleic acid to oleylamine) can alter the photoluminescence (PL) characteristics of the prepared NCs, including the PL-peak wavelength, PL-peak intensity and quantum yield. The highest photoluminescence quantum yield (PLQY) of 13.4% is achieved by the Cs₂SnCl₆ NCs prepared with the volume ratio of oleic acid to oleylamine of 40 μL to 10 μL. A long-term PL stability test demonstrates that the as-synthesized Cs₂SnCl₆ NCs can retain a stable PLQY over a period of 60 days. This work opens up a new path for a large-scale green-route synthesis of blue-emitting Sn-based lead-free NCs, such as Cs₂SnX₆ (Cl, Br and I), towards their applications in optoelectronics.