Pressure-Induced Metallization of the Halide Perovskite (CH₃NH₃)PbI₃

We report the metallization of the hybrid perovskite semiconductor (MA)PbI₃ (MA = CH₃NH₃⁺) with no apparent structural transition. We tracked its bandgap evolution during compression in diamond-anvil cells using absorption spectroscopy and observed strong absorption over both visible and IR wavelengths at pressures above ca. 56 GPa, suggesting the imminent closure of its optical bandgap. The metallic character of (MA)PbI₃ above 60 GPa was confirmed using both IR reflectivity and variable-temperature dc conductivity measurements. The impressive semiconductor properties of halide perovskites have recently been exploited in a multitude of optoelectronic applications. Meanwhile, the study of metallic properties in oxide perovskites has revealed diverse electronic phenomena. Importantly, the mild synthetic routes to halide perovskites and the templating effects of the organic cations allow for fine structural control of the inorganic lattice. Pressure-induced closure of the 1.6 eV bandgap in (MA)PbI₃ demonstrates the promise of the continued study of halide perovskites under a range of thermodynamic conditions, toward realizing wholly new electronic properties.