Mechanical Properties of Formamidinium Halide Perovskites FABX3 (FA=CH(NH2)2; B=Pb, Sn; X=Br, I) by First-Principles Calculations

The mechanical properties of formamidinium halide perovskites FABX(3) (FA=CH(NH2)(2); B=Pb, Sn; X=Br, I) are systematically investigated using first-principles calculations. Our results reveal that FABX(3) perovskites possess excellent mechanical flexibility, ductility and strong anisotropy. We shows that the planar organic cation FA(+) has an important effect on the mechanical properties of FABX(3) perovskites. In addition, our results indicate that (i) the moduli (bulk modulus B, Young's modulus E, and shear modulus G) of FABBr(3) are larger than those of FABI(3) for the same B atom, and (ii) the moduli of FAPbX(3) are larger than those of FASnX(3) for the same halide atom. The reason for the two trends is demonstrated by carefully analyzing the bond strength between B and X atoms based on the projected crystal orbital Hamilton population method.