Metal halide perovskites based on formamidiilium (FA) show interesting properties compared to methyl ammonium (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 first principles 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 SnBr3 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 similar to 1.8 eV up to 85% Sn content, making them interesting candidates for applications in tandem devices.
Exploring the Limits of Three-Dimensional Perovskites: The Case of FAPb1–xSnxBr3
Mosconi, E.;De Angelis, F.
;
2018
Abstract
Metal halide perovskites based on formamidiilium (FA) show interesting properties compared to methyl ammonium (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 first principles 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 SnBr3 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 similar to 1.8 eV up to 85% Sn content, making them interesting candidates for applications in tandem devices.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
