Ultra-stable blue-emitting lead-free double perovskite CsSnCl 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 CsSnCl powders is developed, in which deionized water with a small amount of inorganic acid is used as the solvent and the synthesis of the CsSnCl powders is achieved on a microfluidic platform. Using the CsSnCl powders, we prepare CsSnCl NCs 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 CsSnCl 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 CsSnCl 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 CsSnX (Cl, Br and I), towards their applications in optoelectronics.