Probing the Stability and Band Gaps of Cs₂AgInCl₆ and Cs₂AgSbCl₆ Lead-Free\nDouble Perovskite Nanocrystals

Abstract

Lead\ntoxicity has sparked interest into alternative halide nanomaterials\nwith properties similar to CsPbX₃ perovskites. A promising\nalternative suggested from bulk studies is the family of double perovskites\nof the form Cs₂AgMX₆. Here, we report the synthesis\nof colloidal Cs₂AgInCl₆ and Cs₂AgSbCl₆ nanocrystals via injection of acyl halides into a metal acetate\nsolution under atmospheric conditions and relatively mild temperatures.\nWe demonstrate the synthesis of single-crystalline cubic nanocrystals\nof ca. 10 nm side length and their morphological similarities to other\ndouble perovskite nanostructures in terms of their [200] facet termination\nand decoration with Ag⁽⁰⁾ smaller nanocrystallites. To\ncompare the stabilities of the synthesized materials, we develop a\ntitration assay based on the degradation of nanocrystals with amines\nas a proxy for degradation by humidity, which provides a quantifiable\nstability metric. This measurement shows that Cs₂AgSbCl₆ releases more than twice the decomposition energy compared\nto Cs₂AgInCl₆ or CsPbCl₃ and degrades\nin the presence of approximately one molar equivalent of amine, whereas\nthe other two materials require more than a 100-fold excess. Using\nfacile chemical titration to quantitatively determine chemical stability\nprovides an additional tool to aid in the basic understanding of what\nmakes some of these materials more environmentally stable than others.