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

Abstract

Abstract 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 3 n +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 3 n +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.