Optical Properties of Thin Films of Tin Iodide Perovskite Nanostructures

Abstract Tin halide perovskite nanocrystals (NCs) are less prone to the environmental issues associated with the lead‐based NC analogs, however, they suffer from tin oxidation and structural polymorphism. NC durability deteriorates further in the solid state due to the greater exposure to humidity and oxygen, resulting in a very limited number of studies on thin films of tin halide nanostructures. Herein, a spectroscopic study of 3D CsSnI₃ NCs that coexist with 2D Ruddlesden‐Popper nanosheets (NSs) in residual amounts is being reported. Encapsulation by polystyrene produces solids that are stable in the oxygen‐free environment of the measurements even upon consecutive thermal cycling. At room temperature, strong NC and weak NS excitonic bands are observed in the pump‐probe and photoluminescence (PL) spectra, with bleaching dynamics and PL lifetime of the order of 0.1 and 1 ns, respectively. Spectroscopy supported by hyperspectral microscopy indicates that exciton dynamics are controlled by intrinsic exciton recombination, with minimal influence from NC‐NC and NC‐NS electronic interactions. On the other hand, structural interactions such as binding of the NSs at the surfaces of the CsSnI₃ NCs may explain the formation of trapping sites for excitons and the appearance of bound exciton emission in the cryogenic PL.