Lithium Cycling in a Self-Assembled Copper Chloride–Polyether Hybrid Electrode

Atomic-scale integration of polyether molecules and copper­(II) chloride layers in a two-dimensional perovskite affords, to the best of our knowledge, the first example of extended Li⁺ cycling in a metal chloride electrode. The hybrid can cycle over 200 times as a cathode in a lithium battery with an open-circuit voltage of 3.2 V. In contrast, CuCl₂ alone or the precursors to the hybrid cannot be cycled in a lithium battery, demonstrating the importance of the layered, organic–inorganic architecture. This work shows that appropriate organic groups can enable Li⁺ cycling in inexpensive, nontoxic, metal halide electrodes, which is promising for large-scale applications

Red-to-Black Piezochromism in a Compressible Pb–I–SCN Layered Perovskite

Red-to-Black Piezochromism in a Compressible Pb–I–SCN Layered Perovskit

Self-Assembly of Broadband White-Light Emitters

We use organic cations to template the solution-state assembly of corrugated lead halide layers in bulk crystalline materials. These layered hybrids emit radiation across the entire visible spectrum upon ultraviolet excitation. They are promising as single-source white-light phosphors for use with ultraviolet light-emitting diodes in solid-state lighting devices. The broadband emission provides high color rendition and the chromaticity coordinates of the emission can be tuned through halide substitution. We have isolated materials that emit the “warm” white light sought for many indoor lighting applications as well as “cold” white light that approximates the visible region of the solar spectrum. Material syntheses are inexpensive and scalable and binding agents are not required for film deposition, eliminating problems of binder photodegradation. These well-defined and tunable structures provide a flexible platform for studying the rare phenomenon of intrinsic broadband emission from bulk materials

Red-to-Black Piezochromism in a Compressible Pb–I–SCN Layered Perovskite

Red-to-Black Piezochromism in a Compressible Pb–I–SCN Layered Perovskit

Quinone-Functionalized Carbon Black Cathodes for Lithium Batteries with High Power Densities

Quinone-Functionalized Carbon Black Cathodes for Lithium Batteries with High Power Densitie

Pressure-Induced Conductivity and Yellow-to-Black Piezochromism in a Layered Cu–Cl Hybrid Perovskite

Pressure-induced changes in the electronic structure of two-dimensional Cu-based materials have been a subject of intense study. In particular, the possibility of suppressing the Jahn–Teller distortion of d⁹ Cu centers with applied pressure has been debated over a number of decades. We studied the structural and electronic changes resulting from the application of pressures up to ca. 60 GPa on a two-dimensional copper­(II)–chloride perovskite using diamond anvil cells (DACs), through a combination of in situ powder X-ray diffraction, electronic absorption and vibrational spectroscopy, dc resistivity measurements, and optical observations. Our measurements show that compression of this charge-transfer insulator initially yields a first-order structural phase transition at ca. 4 GPa similar to previous reports on other Cu^II–Cl perovskites, during which the originally translucent yellow solid turns red. Further compression induces a previously unreported phase transition at ca. 8 GPa and dramatic piezochromism from translucent red-orange to opaque black. Two-probe dc resistivity measurements conducted within the DAC show the first instance of appreciable conductivity in Cu^II–Cl perovskites. The conductivity increases by 5 orders of magnitude between 7 and 50 GPa, with a maximum measured conductivity of 2.9 × 10^–4 S·cm^–1 at 51.4 GPa. Electronic absorption spectroscopy and variable-temperature conductivity measurements indicate that the perovskite behaves as a 1.0 eV band-gap semiconductor at 39.7 GPa and has an activation energy for electronic conduction of 0.232(1) eV at 40.2 GPa. Remarkably, all these changes are reversible: the material reverts to a translucent yellow solid upon decompression, and ambient pressure powder X-ray diffraction data taken before and after compression up to 60 GPa show that the original structure is maintained with minimal hysteresis

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

Intrinsic White-Light Emission from Layered Hybrid Perovskites

We report on the second family of layered perovskite white-light emitters with improved photoluminescence quantum efficiencies (PLQEs). Upon near-ultraviolet excitation, two new Pb–Cl and Pb–Br perovskites emit broadband “cold” and “warm” white light, respectively, with high color rendition. Emission from large, single crystals indicates an origin from the bulk material and not surface defect sites. The Pb–Br perovskite has a PLQE of 9%, which is undiminished after 3 months of continuous irradiation. Our mechanistic studies indicate that the emission has contributions from strong electron–phonon coupling in a deformable lattice and from a distribution of intrinsic trap states. These hybrids provide a tunable platform for combining the facile processability of organic materials with the structural definition of crystalline, inorganic solids

Broadband Emission with a Massive Stokes Shift from Sulfonium Pb–Br Hybrids

Broadband Emission with a Massive Stokes Shift from Sulfonium Pb–Br Hybrid

Broadband Emission with a Massive Stokes Shift from Sulfonium Pb–Br Hybrids

Broadband Emission with a Massive Stokes Shift from Sulfonium Pb–Br Hybrid