Probing the Role of Local Structure in Driving the Stability of Halide Perovskites CH3NH3PbX3

Organic-inorganic lead halide perovskites have rapidly emerged as one of the leading contenders in optoelectronic and photovoltaic technology, but they show stability issues. Among methylammonium (MA) lead bromide and MA lead iodide, the Br counterpart is reported to exhibit improved stability under ambient conditions. However, the underlying fundamentals of such an enhancement are not fully understood. Using temperature-dependent X-ray diffraction and extended X-ray absorption fine structure measurements, we find relatively reduced value of linear coefficient of thermal expansion, elevated Einstein temperature, and reduced dynamic disorder in MAPbBr(3) compared to MAPbI(3) which implies that a relatively rigid Pb-Br bond offers steric hindrance to the migration of bulky MA ion resulting in improved stability of MAPbBr(3).

Automated summary

Utilizing temperature-dependent X-ray diffraction and extended X-ray absorption fine structure measurements, it is found that MAPbBr(3) displays relatively reduced linear coefficient of thermal expansion, elevated Einstein temperature, and reduced dynamic disorder compared to MAPbI(3), suggesting that a relatively rigid Pb-Br bond inhibits the migration of MA ions and leads to improved stability.