Local structure, bonding, and asymmetry of ((NH2)2CH)PbBr3, CsPbBr3

The local structure of hybrid organic-inorganic halide perovskites is of considerable interest due to the impact on optoelectronic and ion-conducting properties. Here, it is shown that the lead bromide perovskites are nearly perfect at low temperature, with negligible static disorder, through a temperature-dependent x-ray absorption spectroscopy study. As the crystal heats up, two things happen: the organic molecular-ion motion changes the Pb-Br bond strength at the orthorhombic-tetragonal transition, and anharmonicity (${C}_{3})$ contributes to a significant thermal disorder at room temperature.