부산대학교 도서관

The organic cation dynamics in organic–inorganic hybrid perovskites strongly affect the power energy conversion and unique physical properties of these materials. To date, the first-principles rotational potential energy surface (PES) of formamidinium (FA) has not been reported. Thus, we examined the rotational energy barriers for FA in cubic-phase perovskites (FABX3(B = Sn/Pb; X = Cl/Br/I)) by density functional theory and compared these with those of methylammonium. The calculated rotational PES of FAPbI3indicates that FA rotates around the N–N bond axis (φ) with a low energy barrier, whereas the energy barrier for FA rotation around the axis penetrating the C atom and the center of gravity of FA (θ) is high. Moreover, the φ and θ rotational barriers of FA increase with halogen substitution. Thus, we reveal important design rules for controlling the rotational barrier and orientation by forming hydrogen bonds and halogen substitution.