Tips and Twists in Making High Photoluminescence Quantum Yield Perovskite Nanocrystals

Abstract

Making nanocrystals in a reaction flask is always exciting. This is even more fun with visible light-emitting nanocrystals. After the workhorse CdSe,(1) CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals emerged as the next all-visible color tunable emitters in nanodimensions.(2) While the synthesis of both of these types of semiconductor nanocrystals employed colloidal hot injection reactions, but perovskite nanocrystals showed unprecedented high photoluminescence quantum yield (PLQY). Hence, these nanocrystals remained in the forefront of current research and are considered as an efficient lighting material for energy conversion. However, the root of the performance in any kind of lighting application remains the quality of the material, which in turn depends on the synthetic strategy in the reaction flask. During the last four years, significant improvements have been achieved in optimizing the synthesis and obtaining near-unity PLQYs for all blue, green, and red emitting perovskite nanocrystals. The high-temperature synthetic approach, originally developed by Kovalenko et al.,(2) remained the benchmark protocol for obtaining these high-quality nanocrystals. This has been further modified, and the reaction chemistry for the formation of all three of these halide perovskite nanocrystals has been widely investigated.(3−11) Analysis of the chronological developments with variations of precursor ratios, ligands, reaction temperature, and also the solvent suggests that each successive modification has a logic behind the optimization of the reaction. This also helps in formulating the precise reaction parameters for obtaining the near-unity PLQY for all three CsPbX3 (X = Cl, Br, and I) nanocrystals in a reaction flask. Compiling all these developments, the step-by-step progress of reactions in the synthesis of these perovskite nanocrystals, is discussed in this Viewpoint. Some synthesis tips and also some tricks for avoiding phase change or quenching of photoluminescence (PL) of these nanocrystals are also discussed.