In this paper we provide an accurate high-pressure structural and optical study of MAPbI3 hybrid perovskite. Structural data show the presence of a phase transition towards an orthorhombic structure around 0.3 GPa followed by full amorphization of the system above 3 GPa. After releasing pressure the systems keeps the high-pressure orthorhombic phase. The occurrence of these structural transitions is further confirmed by pressure induced variations of the photoluminescence signal at high pressure. These variations clearly indicate that the bandgap value and the electronic structure of MAPI change across the phase transition.3

Wide modulation of the band gap induced by organic cation replacement in the FA1−xMAxSnBr3 (0 ≤ x ≤ 1) solid solution.

Metal halide perovskites based on formamidinium (FA) show interesting properties compared to methylammonium (MA) compounds. The larger molecular size of FA compared to that of MA leads, however, to a structural instability in FAPbI 3 , placing FA at the border of tolerance factor for three-dimensional (3D) lead iodide perovskites. Because of the huge interest in mixed Sn/Pb perovskites, here we investigate FAPb 1−x Sn x Br 3 perovskites in a full compositional range (0 ≤ x ≤ 1). We find a non-monotonic band gap evolution with increasing Sn content, which, through firstprinciples computational analyses, we relate to a distorted structure that dynamically averages to a cubic phase, as determined by X-ray diffraction. The large FA cation induces an instantaneous structure made by partly decoupled SnBr 3 units, which leads to the observed band gap opening. FASnBr 3 thus likely represents a limit compound of 3D perovskites. Intermediate FAPb 1−x Sn x Br 3 compositions maintain a band gap of ∼1.8 eV up to 85% Sn content, making them interesting candidates for applications in tandem devices.

A novel air-stable Sn-based hybrid perovskite system, MA1−xDMAxSnBr3, system is provided.