Kinetically Controlled Growth of Sub-Millimeter 2D Cs₂ SnI₆ Nanosheets at the Liquid-Liquid Interface

Cs₂ SnI₆ perovskite displays excellent air stability and a high absorption coefficient, promising for photovoltaic and optoelectronic applications. However, Cs₂ SnI₆ -based device performance is still low as a result of lacking optimized synthesis approaches to obtain high quality Cs₂ SnI₆ crystals. Here, a new simple method to synthesize single crystalline Cs₂ SnI₆ perovskite at a liquid-liquid interface is reported. By controlling solvent conditions and Cs₂ SnI₆ supersaturation at the liquid-liquid interface, Cs₂ SnI₆ crystals can be obtained from 3D to 2D growth with controlled geometries such as octahedron, pyramid, hexagon, and triangular nanosheets. The formation mechanisms and kinetics of complex shapes/geometries of high quality Cs₂ SnI₆ crystals are investigated. Freestanding single crystalline 2D nanosheets can be fabricated as thin as 25 nm, and the lateral size can be controlled up to sub-millimeter regime. Electronic property of the high quality Cs₂ SnI₆ 2D nanosheets is also characterized, featuring a n-type conduction with a high carrier mobility of 35 cm² V^-1 s^-1 . The interfacial reaction-controlled synthesis of high-quality crystals and mechanistic understanding of the crystal growth allow to realize rational design of materials, and the manipulation of crystal growth can be beneficial to achieve desired properties for potential functional applications.