Manipulating the phase transitions and the appearance of a “black phase” in cyclically compressed CH3NH3PbBr3 perovskite

Abstract

Lead halide hybrid perovskites have excellent optoelectronic properties and find applications in solar cells and other devices. Strongly different compressibilities of their inorganic and organic subsystems make them highly sensitive to applied stresses, but, simultaneously, can lead to structural disordering under moderate applied stresses. Herein, in the example of single-crystalline CH₃NH₃PbBr₃ (methylammonium lead bromine perovskite, MAPbBr₃), subjected to an extreme treatment of cyclic high pressures up to 10 GPa, we discovered several novel insights. (i) Cyclic high pressure treatments up to 5 GPa, below a disordering point, can significantly manipulate the phase stability ranges, whereas, treatments across the disordering point result in the restoration of the original characteristics. (ii) High-pressure treatments can lead to complete breakdown of the perovskite structure. For MAPbBr₃, this is seen by the appearance of an enigmatic “black phase”. (iii) A nearly complete restoration of single crystallinity after multiple pressure-driven disordering indicated the presence of strong self-healing effects. We performed very accurate in situ measurements of electrical resistance for four single crystals of MAPbBr₃ over multiple cycles of compression and decompression, enabling precise tracking of the phase transitions. We proposed that changes in the phase stability ranges can result from the emergence of structural defects, forming new chemical bonds. Our results for the example of MAPbBr₃ demonstrated that by using high-pressure treatment, one can modify inorganic–organic hybrid perovskites and manipulate their phase stability ranges.