Hybrid perovskites under pressure: Present and future directions

Hybrid organic–inorganic perovskites (HOIPs) have emerged as outstanding candidates for high-performance photovoltaic devices, and a large variety of HOIPs has been synthesized with different compositions and structural motifs. However, issues remain about their stability and optimization for applications, motivating studies to provide better insight into understanding the structure-property relationship. The application of pressure has proven to be a valuable tool to reach this goal without altering the chemical composition. Indeed, through compression, the atomic and electronic structures of HOIPs can be both finely tuned and dramatically changed, leading to bandgap reduction, phase transitions, and even semiconductor-to-metal transition. In this Perspective, we first provide a general overview of HOIPs, introducing their structure and properties at ambient conditions, focusing only on fully hybrid metal halide perovskites, and thus neglecting the inorganic counterparts. Second, we review and summarize the findings of previous high-pressure research works on these materials, highlighting the common patterns in their high-pressure behavior. We then give an outlook of the main gaps in present work that needs to be filled in our opinion and suggest possible future directions for high-pressure research program on HOIPs. Finally, we provide a first example of such future investigations presenting a preliminary high-pressure low-temperature phase diagram of MAPbBr3 established through synchrotron x-ray diffraction and infrared spectroscopy.