Solvent-Free Preparation and Moderate Congruent Melting Temperature of Layered Lead Iodide Perovskites for Thin-Film Formation.

Lead halide 2D hybrid perovskites (HP) have emerged as promising materials for photovoltaic and lighting applications. Solvent-free preparations offer greener route, but require congruent melting of halide perovskite for thin films, which has been demonstrated only for monolayered HP (n=1 of the (A) (MA) Pb I series) at the quite high temperature T (T ) of 171 °C. Here, we report on the solvent-free preparation (n=2, 4), thermal behaviour and melt-processed thin films of a series of HP (GABA) (MA) Pb I (n=1, 2, 4; GABA : 4-ammoniumbutyric acid cation). The n=1 and n=2 HP have an exceptional low congruent T of 126 °C and 136 °C, respectively, and, for n=1, a very good stability in the molten state. The liquid-solid reaction of molten (GABA) PbI or (GABA) (MA)Pb I with MAPbI in 1/1 (T=130 °C) or 1/2 (T=135 °C) ratio leads to pure phases of the n=2 HP and (GABA) (MA) Pb I (n=4, T =185 °C), respectively. Melt-processed thin films of n=1, n=2 and n=4 HP have also been prepared.