Synthesis and Perspectives of Oriented Growth of Double-Perovskite Cs2SnI6 in the Presence of Antimony

Vacancy-ordered double-perovskite Cs2SnI6 is known to be a good candidate for perovskite photovoltaics, as it is a light harvesting material which has potential both as an individual compound and as a component of a composite material. The compound is interesting due to being free of atom sites in B cationic positions, making the lattice “breathable” and giving it optoelectronic characteristics that vary with dopants. Here, antimony was examined as a possible heterovalent dopant with an ionic radius larger than that of Sn4+. In practice, it has been found that most of the materials are composites of Cs2SnI6 and Cs3Sb2I9 phases. In the CsI–SnI4–SbI3 phase triangle, the melt crystallization process produced a layered (111)-oriented microstructure of crystallites with an increasing percentage of antimony. Two-dimensional perovskite materials look more promising in the decomposition of a solid solution to Cs2SnI6 and Cs3Sb2I9 phases than in heterophase nucleation. The observed effect of (111)-oriented growth could be translated to other inorganic halides to form new oriented films or single crystals of perovskite materials. Diffuse reflectance spectroscopy showed an additional absorption shoulder in the NIR region for all groups of compounds, most likely induced by point defects in I sublattices of Cs2SnI6. Expanding the Cs2SnI6 absorption range to the NIR region could lead to new perspectives for its application.