Ligand-Size Related Dimensionality Control in Metal Halide Perovskites

Low-dimensional organic-inorganic hybrid perovskites have triggered many fundamental research studies due to their intrinsic tunable photovoltaic properties, technologically relevant stability, and promising efficiency. However, there is limited information on how ligand size influences inherent structural and electronic properties of perovskites. To gain deeper understanding of ligand-size related structural and film properties, we fabricated a series of (L)(2)(MA)(n-1)PbnI3n+1 materials by introducing organic spacer ligands of n-CH3CH2NH3 (EA), n-CH3(CH2)(2)NH3 (PA), and n-CH3(CH2)(3)NH3 (BA) into the three-dimensional (3D) methylammonium (MA) lead iodide (MAPbI(3)) system with the same inorganic layer thickness (average < n > = 4). We demonstrate that the increased number of carbon atoms on ligands affects compatibility of ligands with the 3D [PbI6](4-) framework, leading to different structural dimensionality and crystal orientation, largely explaining different electronic properties, crystal stability, and the consequent device performance of solar cells. This work provides key missing information on how ligand size influences structural dimensionality and desirable electronic properties for future stable and efficient solar cells.