Shape tunable two−dimensional ligand−free cesium antimony chloride perovskites

Abstract

Organic ligands play a key role in determining the shape and stability of the perovskite nanocrystals (NCs). However, the ligands often create poor stability and defects through imperfect attachment, in addition to the post synthesis detachment. We developed a novel route to synthesize the ligand−free ambient stable two−dimensional (2D) cesium antimony chloride (Cs3Sb2Cl9) NCs. First, hexagonal shape NCs are synthesized through a fast one−step reaction at room temperature using a reprecipitation method. The shape of hexagonal NCs is further tuned into well−defined 2D plates through a solid-state temperature-driven crystal phase transition. In−situ variable temperature X−ray diffraction and differential scanning calorimetry cycles probe temperature-sensitive metastability and irreversibility of trigonal to orthorhombic crystallographic phase transition. Rietveld analyses quantify volume fractions and coherently diffracting crystallite domains that promote the growth of the two crystal phases. Both the hexagonal NCs and plates show ambient structural stability for over months. The proposed formation mechanism can guide to improve synthetic methods to realize ligand−free shape-controlled perovskite NCs.