Glassy Flux Protocol to Confine Lead-Free CsSnX₃ Nanocrystals into Transparent Solid Medium

Encapsulation of halide perovskites into a transparent solid medium is important for increasing their stability and rendering the exploration of new optoelectronic applications. Here, we describe a glassy flux protocol to confine lead-free cesium tin halide (CsSnX₃) perovskite nanocrystals into a transparent chalcogenide glassy matrix by capitalizing on judiciously designed germanium-antimony-sulfur chalcogenide flux as a solvent to dissolve and recrystallize the target crystal phases. We show that CsSnX₃ nanocrystals can be obtained in the form of a spherical shape, single crystalline, and with an arbitrary halide ratio through the use of cesium halide and tin(II) halide at precisely defined concentrations. The grain size and size distribution of CsSnX₃ nanocrystals are rationally tuned by Ostwald-ripening-controlled crystallization of CsSnX₃ supersaturated metastable glasses. The present work suggests that the traditional flux technique could be adopted inversely for materials discovery of new nanocomposites through a simple protocol of the dissolution of target nanocrystals into an inert transparent glassy flux.