2024 AIChE Annual Meeting
Small Angle X-Ray Scattering of Metal Halide Perovskite Nanocrystals
From photocatalysis to optoelectronics, metal halide perovskite nanocrystals are an incredibly promising material. Notably, they have a high photoluminescence quantum yield, narrow emission linewidth, and precise tunability of their band gap by adjusting both size and halide composition. A major issue with the colloidal synthesis of these materials is the occurrence of a size distribution of nanocrystals, driving inhomogeneous broadening. In a quantum confined regime, different sized particles emit different frequencies, causing the overall emission spectra to broaden - ultimately impacting the purity of the energy emitted by the material. Due to this major size dependency on the uniformity of the material produced, precise size control of colloidal nanoparticle synthesis is integral. One technique for characterizing the size and shape of nanocrystals is small angle x-ray scattering (SAXS) which can provide robust insights into their morphology. In this study, SAXS was used to investigate two main questions related to colloidal CsPbBr₃ nanocrystals: the origin of an asymmetric red-tail shift observed in its photoluminescent spectra and the impact of different surface ligands on the size, size distribution, and shape of nanocrystal solutions. By analyzing SAXS data with different shape models, these factors were compared across a series of samples. While the symmetry of the size distribution did not have a significant impact on presence of a red tail, different surface ligands, such as lecithin, affected both the size and shape of the nanocrystal solution in a distinguishable manner - such as trends in the emission linewidth and photoluminescent quantum yield. Future work involves more robust characterization, modeling, and analysis of additional samples to further connect structural properties of CsPbBr3 nanocrystals to optoelectronic performance.