Hybrid perovskites under pressure: Present and future directions

Abstract

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.

Pressure-Induced Phase Transition versus Amorphization in Hybrid Methylammonium Lead Bromide Perovskite

“…The crystal structure of these compounds can be described as an inorganic sub-lattice of corner-sharing PbBr 6 (PbI 6 ) octahedral units hosting the MA molecules . Because of the high compressibility of the inorganic host lattice and the organic molecule, the crystal structure of hybrid perovskites can be easily modified applying an external pressure . In the case of MAPbBr 3 , two phase transitions have been reported below 4.6 GPa. − Pressure modifies not only the crystal structure but also the electronic properties, including the band-gap energy, thereby becoming a powerful tool to strengthen the current understanding of the properties of MAPbBr 3 as well as other HOIPs, and to provide information relevant for optimizing the photovoltaic performance .…”

“…Because of the high compressibility of the inorganic host lattice and the organic molecule, the crystal structure of hybrid perovskites can be easily modified applying an external pressure . In the case of MAPbBr 3 , two phase transitions have been reported below 4.6 GPa. − Pressure modifies not only the crystal structure but also the electronic properties, including the band-gap energy, thereby becoming a powerful tool to strengthen the current understanding of the properties of MAPbBr 3 as well as other HOIPs, and to provide information relevant for optimizing the photovoltaic performance . Regarding the crystal structure, a recent single-crystal X-ray diffraction study revealed that MAPbBr 3 undergoes two phase transitions following the space-group sequence: Pm 3̅ m → Im 3̅→ Pmn 2 1 .…”

“…Over the last decades, hybrid organic–inorganic perovskites (HOIPs) have experienced a stunning development because they are outstanding light-absorbing materials for highly efficient photovoltaic cells. 1 Among HOIPs, methylammonium (MA, CH 3 NH 3 ) lead halide perovskites, such as MAPbBr 3 and MAPbI 3 , have received the most attention and perovskite solar cells have consequently achieved a photovoltaic efficiency of 25%. 2 The crystal structure of these compounds can be described as an inorganic sub-lattice of corner-sharing PbBr 6 (PbI 6 ) octahedral units hosting the MA molecules.…”

Temperature- and Pressure-Dependent Raman and Photoluminescence Studies of Corrugated Imidazolium-Methylhydrazinium Lead Bromide

“…This type of behavior suggests that interactions above 7.0 GPa between organic cations and inorganic substructure become so strong that they lead to distortion of both organic cations and PbBr 6 octahedra, as well as increased octahedral tilting. This static disorder was observed in different 3D and some (001)-oriented lead halides. ,− However, in case of (001)-oriented perovskites, this static disorder was usually observed at larger pressure than in our case, i.e., 9.2 GPa for (C 6 H 5 CH 2 NH 3 ) 2 PbI 4 and 8.2 GPa for (C 6 H 5 CH 2 CH 2 NH 3 ) 2 PbBr 4 . , The static disorder process and pressure-induced phase transition are reversible, as evidenced by reappearance of the bands during decompression and recovery of the ambient pressure phase at 0.01 GPa (Figure S4).…”

Anomalous Electron–Phonon Coupling in Cesium-Substituted Methylammonium Lead Iodide Perovskites

“…Hence, TE causes a gap reduction. However, lead halide perovskites are an exception in terms of the sign of the gap pressure coefficient (see ref and references therein).…”