(757c) Solution-Based Synthesis of Chalcogenide Perovskite

Halide perovskite has achieved great success due to its high power conversion efficiency up to around 30%. But its instability to air and moisture remains to be a challenging project. As a possible candidate, oxide perovskite has gained a lot of attention during the past decade, as it is insensitive to air or moisture. Unlikely, chalcogenide perovskite has been rarely reported, while it is also more stable in air and moisture than halide perovskite and promising for photovoltaic applications according to DFT simulations. As opposed to synthesis of halide and oxide perovskite, synthesis of chalcogenide reported so far is limited to solid-phase reactions, namely two solid metal precursors mixture reacts into the target perovskite under sulfur-source gas, extremely high temperature, and sometimes high pressure. The low efficiency of solid-phase reaction, high temperature, high pressure, and hazardous sulfur-source gas are the main factors limiting the scalability of chalcogenide perovskite synthesis, not to mention the versatility of the current strategy. In light of that halide and oxide perovskites can both be synthesized readily in solution, it is theoretically possible chalcogenide perovskite can also be synthesized using a solution-based reaction. Since it is preferential to form the same perovskite structure with O than S due to much higher reactivity of O, it is only possible for the formation of chalcogenide perovskite structure when the reaction is water and oxygen free. Therefore, the key point of the reaction is to find soluble metal precursors soluble in organic solvent at the same time. Fortunately, we found a type of organic salts researched thoroughly before 1990s, which were extensively used for nanocrystal growth in oleylamine. Due to the solubility, and only C, H, N, S containing property, these organic salts are the ideal precursors for solution-based chalcogenide perovskite growth.

Inspired by this, we have used these organic salts to prepare ABX₃ chalcogenides, BaSnS₃ and BaZrS₃ respectively. BaSnS₃ turns out to have a needle-like crystal structure while BaZrS₃ has a perovskite structure. Both structures are verified by X-ray diffraction (XRD) patterns and selected area electron diffraction (SAED) in TEM. This work is instructive for preparations of other promising chalcogenide perovskites with similar structures proposed by simulation works.