Nanocrystal Synthesis Derived Approach to Silver Bismuth Iodide Layered Double Perovskites with Aliphatic Amines: (C <i> _n </i> H _{(2 <i>n</i> +1)} NH ₃ ) ₄ AgBiI ₈

Lead-free iodide double perovskites are an interesting class of materials since they combine a relatively low toxicity (compared to the lead counterpart) with the small band gap typical of iodide-based perovskite structures. Their reported number is small due to their lower structural stability compared to the chloride and bromide analogues; hence, their synthesis is difficult. The structural constraints that limit stability, on the other hand, can be much relieved in layered organic-inorganic perovskites. Following this line of thought, we report here a successful fast precipitation route to iodide layered (C _<i>n</i> H_{(2<i>n</i>+1)}NH₃)₄AgBiI₈ (<i>n</i> = 10, 12, and 14) double perovskites that borrow concepts from the synthesis of colloidal nanocrystals. X-ray diffraction studies revealed for these compounds a monoclinic crystal structure containing edge-sharing-alternating [AgI₆] and [BiI₆] octahedra. These materials have experimental band gaps of 2.1 eV, as also corroborated by theoretical calculations. We have also investigated their phase transitions by thermal analysis and temperature-dependent diffraction and found them to be similar to their lead-based layered perovskite counterparts.