Compression with gigapascal-scale pressures can yield dramatic structural and electronic changes in solids. Understanding correlations between pressure-induced structural and electronic changes allows us to use compression as a tuning knob for accessing new material properties. Furthermore, the compressibility of organic-inorganic hybrids can be modulated by fine-tuning both organic and inorganic components. In this talk, I will discuss the dramatic effects of applied pressure, of up to 50 GPa, on both 2D and 3D hybrid perovskites. 2D perovskites: The d9 Cu centers in Cu−Cl perovskites display a prominent Jahn-Teller (JT) distortion, which contributes to the materials’ insulating nature. The question of whether applied pressure can suppress such a JT distortion has been extensively debated in the literature. By applying pressures above the theoretical minimum required to relieve the JT distortion, we see an unprecedented color change in the perovskite, from translucent yellow to opaque black, and an increase in electronic conductivity of more than 5 orders of magnitude. Using a suite of spectroscopic probes, we find that the JT distortion is at least partially relieved at high pressures to provide a new electronic conduction pathway. Our recent studies on an analogous 2D Pb−I−SCN perovskite reveal a far more compressible material, whose color changes from red to black at a much lower pressure. 3D perovskites: Using atomic coordinates from the first single-crystal structures of the high-pressure phases of (CH3NH3)PbI3 and (CH3NH3)PbBr3, we track structural evolution upon compression. These structural changes explain why the solids first lighten in color and then become opaque black with compression. High-pressure resistivity measurements show that the Pb−I perovskite approaches a metallic transition at ca. 50 GPa. We also find that applied pressure can mitigate light-induced instabilities in mixed-halide perovskites, affording higher voltages from devices employing these absorbers.

Hybrid perovskites under pressure: Accessing new properties through lattice compression

253rd National Meeting (2017)

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