Polymorphism in metal halide perovskites

Metal halide perovskites (MHPs) are frontrunners among solution-processable materials for lightweight, large-area and flexible optoelectronics. These materials, with the general chemical formula AMX(3), are structurally complex, undergoing multiple polymorph transitions as a function of temperature and pressure. In this review, we provide a detailed overview of polymorphism in three-dimensional MHPs as a function of composition, with A = Cs+, MA(+), or FA(+), M = Pb2+ or Sn2+, and X = Cl-, Br-, or I-. In general, perovskites adopt a highly symmetric cubic structure at elevated temperatures. With decreasing temperatures, the corner-sharing MX6 octahedra tilt with respect to one another, resulting in multiple polymorph transitions to lower-symmetry tetragonal and orthorhombic structures. The temperatures at which these phase transitions occur can be tuned via different strategies, including crystal size reduction, confinement in scaffolds and (de-)pressurization. As discussed in the final section of this review, these solid-state phase transformations can significantly affect optoelectronic properties. Understanding factors governing these transitions is thus critical to the development of high-performance, stable devices.

Automated summary

Metal halide perovskites are advanced materials for optoelectronic devices, with complex structures that undergo polymorph transitions with temperature and pressure. The phase transition temperatures can be tuned via various strategies, significantly affecting optoelectronic properties. Understanding factors governing these transitions is crucial for developing high-performance, stable devices.