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) 2 (MA) n-1 Pb n I 3n+1 series) at the quite high temperature T m (T melting ) 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) 2 (MA) n-1 Pb n I 3n+1 (n=1, 2, 4; GABA + : 4-ammoniumbutyric acid cation). The n=1 and n=2 HP have an exceptional low congruent T m 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) 2 PbI 4 or (GABA) 2 (MA)Pb 2 I 7 with MAPbI 3 in 1/1 (T=130 °C) or 1/2 (T=135 °C) ratio leads to pure phases of the n=2 HP and (GABA) 2 (MA) 3 Pb 4 I 11 (n=4, T m =185 °C), respectively. Melt-processed thin films of n=1, n=2 and n=4 HP have also been prepared.