Self-Assembly\nof CsPbBr₃ Nanocubes into\n2D Nanosheets

Abstract

All-inorganic metal halide perovskites\nhave attracted considerable\nattention due to their high application potentials in optoelectronics,\nphotonics, and energy conversion. Herein, two-dimensional (2D) CsPbBr₃ nanosheets with a thickness of about 3 nm have been synthesized\nthrough a simple chemical process based on a hot-injection technique.\nThe lateral dimension of CsPbBr₃ nanosheets ranges from\n11 to 110 nm, which can be tuned by adjusting the ratio of short ligands\n(octanoic acid and octylamine) over long ligands (oleic acid and oleylamine).\nThe nanosheets result from the self-assembly of CsPbBr₃ nanocubes with an edge length of about 3 nm, which possess the same\ncrystal orientation. In addition, an amorphous region of about 1 nm\nin width is found between adjacent nanocubes. To investigate both\nthe structure and the growth mechanism of these nanosheets, microstructural\ncharacterizations at the atomic scale are conducted, combined with\nX-ray diffraction analysis, ¹H nuclear magnetic resonance\n(¹H NMR) measurement, and density functional theory (DFT)\ncalculation, aiming to determine the configuration of different ligands\nadsorbed onto CsPbBr₃. Our results suggest that the adjacent\nnanocubes are mainly connected together by short ligands and inclined\nlong ligands. On the basis of the DFT calculation results, a relationship\nis derived for the volume ratio of short ligands over long ligands\nand the lateral dimensions of CsPbBr₃ nanosheets. Moreover,\na physicochemical mechanism is proposed to explain the 2D growth of\nCsPbBr₃ nanosheets. Such a finding provides new insights\nregarding the well-ordered self-arrangement of CsPbBr₃ nanomaterials,\nas well as new routes to synthesize 2D CsPbX₃ (X = Cl and\nI) nanosheets of suitable dimensions for specific and large-scale\napplications.