Colloidal Metal-Halide Epitaxial Heterostructures: From Serendipity to Rational Design

Colloidal epitaxial heterostructures are nanoparticles made of two crystalline materials connected at an interface. These architectures profitably combine the properties of their components, and can express unique ones stemming from their interactions. Historically, heterostructures have produced major breakthroughs in the field of colloidal nanomaterials, with core/shell quantum dots being the most renowned examples. Indeed, heterostructures are often grown from isostructural materials like CdSe/CdS, where the only requirements are similar lattice parameters. However, the increasing number of heterostructures reported between non-isostructural materials points to the limits of this design strategy. In this talk, we will take the serendipitous discovery of heterostructures between lead halide perovskites (CsPbX₃) and lead sulfohalides (Pb₄S₃X₂) as a case study.[1,2] We will first identify empirical criteria behind the formation of these heterostructures by comparing them with other interfaces formed by lead halides.[3] Then, we will exploit in-situ spectroscopies performed directly in the liquid reaction medium to gain insight into the growth mechanism of these composite nanomaterials. As a next step, we will take advantage of such knowledge to master the synthesis of two competing nanomaterials (Pb₄S₃Cl₂vs Pb₃S₂Cl₂) by exploiting heterostructures as phase-selective reaction intermediates.[4] This approach is inspired by the retrosynthetic strategies typical of organic chemistry, and provides advanced control over the product of colloidal syntheses. Finally, we will rationalize these results with the help of a novel computational tool, which we designed specifically for predicting the formation of stable colloidal epitaxial heterostructures. By providing fundamental insights into the growth mechanism and stability of colloidal nanocrystal heterostructures, we hope to lower the barrier that separates the widely appealing properties of these fascinating composite nanomaterials from real-world applications.<br/><br/>1) Toso, S. et al. Nanocrystals of Lead Chalcohalides: A Series of Kinetically Trapped Metastable Nanostructures. Journal of the American Chemical Society vol. 142 10198–10211 (2020).<br/>2) Imran, M. et al. Halide Perovskite–Lead Chalcohalide Nanocrystal Heterostructures. Journal of the American Chemical Society vol. 143 1435–1446 (2021).<br/>3) Toso, S. et al. Hidden in Plain Sight: The Overlooked Influence of the Cs+ Substructure on Transformations in Cesium Lead Halide Nanocrystals. ACS Energy Letters vol. 5 3409–3414 (2020).<br/>4) Toso, S. et al. Halide perovskites as disposable epitaxial templates for the phase-selective synthesis of lead sulfochloride nanocrystals. Nature Communications vol. 13 (2022).