title: High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites and Pressure Effects on their Electronic and Optical Properties.
abstract: We report the first high-pressure single-crystal structures of hybrid perovskites. The crystalline semiconductors (MA)PbX3 (MA = CH3NH3 (+), X = Br(-) or I(-)) afford us the rare opportunity of understanding how compression modulates their structures and thereby their optoelectronic properties. Using atomic coordinates obtained from high-pressure single-crystal X-ray diffraction we track the perovskites' precise structural evolution upon compression. These structural changes correlate well with pressure-dependent single-crystal photoluminescence (PL) spectra and high-pressure bandgaps derived from density functional theory. We further observe dramatic piezochromism where the solids become lighter in color and then transition to opaque black with compression. Indeed, electronic conductivity measurements of (MA)PbI3 obtained within a diamond-anvil cell show that the material's resistivity decreases by 3 orders of magnitude between 0 and 51 GPa. The activation energy for conduction at 51 GPa is only 13.2(3) meV, suggesting that the perovskite is approaching a metallic state. Furthermore, the pressure response of mixed-halide perovskites shows new luminescent states that emerge at elevated pressures. We recently reported that the perovskites (MA)Pb(Br x I1-x )3 (0.2 < x < 1) reversibly form light-induced trap states, which pin their PL to a low energy. This may explain the low voltages obtained from solar cells employing these absorbers. Our high-pressure PL data indicate that compression can mitigate this PL redshift and may afford higher steady-state voltages from these absorbers. These studies show that pressure can significantly alter the transport and thermodynamic properties of these technologically important semiconductors.
authors.affiliation: Departments of Chemistry and Geological Sciences, Stanford University , Stanford, California 94305, United States.
authors.forename: Adam
authors.initials: A
authors.lastname: Jaffe
authors.affiliation: Departments of Chemistry and Geological Sciences, Stanford University, Stanford, California 94305, United States; Departments of Chemistry and Geological Sciences, Stanford University, Stanford, California 94305, United States; Photon Science and Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States.
authors.forename: Yu
authors.initials: Y
authors.lastname: Lin
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Christine M
authors.initials: CM
authors.lastname: Beavers
authors.affiliation: SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
authors.forename: Johannes
authors.initials: J
authors.lastname: Voss
authors.affiliation: Departments of Chemistry and Geological Sciences, Stanford University, Stanford, California 94305, United States; Photon Science and Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States.
authors.forename: Wendy L
authors.initials: WL
authors.lastname: Mao
authors.affiliation: Departments of Chemistry and Geological Sciences, Stanford University , Stanford, California 94305, United States.
authors.forename: Hemamala I
authors.initials: HI
authors.lastname: Karunadasa