Tuning the bandgap of Cs2AgBiBr6 through dilute tin alloying.

The promise of lead halide hybrid perovskites for optoelectronic applications makes finding less-toxic alternatives a priority. The double perovskite Cs2AgBiBr6 (1) represents one such alternative, offering long carrier lifetimes and greater stability under ambient conditions. However, the large and indirect 1.95 eV bandgap hinders its potential as a solar absorber. Here we report that alloying crystals of 1 with up to 1 atom% Sn results in a bandgap reduction of up to ca. 0.5 eV while maintaining low toxicity. Crystals can be alloyed with up to 1 atom% Sn and the predominant substitution pathway appears to be a ∼2 : 1 substitution of Sn2+ and Sn4+ for Ag+ and Bi3+, respectively, with Ag+ vacancies providing charge compensation. Spincoated films of 1 accommodate a higher Sn loading, up to 4 atom% Sn, where we see mostly Sn2+ substitution for both Ag+ and Bi3+. Density functional theory (DFT) calculations ascribe the bandgap redshift to the introduction of Sn impurity bands below the conduction band minimum of the host lattice. Using optical absorption spectroscopy, photothermal deflection spectroscopy, X-ray absorption spectroscopy, 119Sn NMR, redox titration, single-crystal and powder X-ray diffraction, multiple elemental analysis and imaging techniques, and DFT calculations, we provide a detailed analysis of the Sn content and oxidation state, dominant substitution sites, and charge-compensating defects in Sn-alloyed Cs2AgBiBr6 (1:Sn) crystals and films. An understanding of heterovalent alloying in halide double perovskites opens the door to a wider breadth of potential alloying agents for manipulating their band structures in a predictable manner

Light-induced picosecond rotational disordering of the inorganic sublattice in hybrid perovskites.

Femtosecond resolution electron scattering techniques are applied to resolve the first atomic-scale steps following absorption of a photon in the prototypical hybrid perovskite methylammonium lead iodide. Following above-gap photoexcitation, we directly resolve the transfer of energy from hot carriers to the lattice by recording changes in the mean square atomic displacements on 10-ps time scales. Measurements of the time-dependent pair distribution function show an unexpected broadening of the iodine-iodine correlation function while preserving the Pb-I distance. This indicates the formation of a rotationally disordered halide octahedral structure developing on picosecond time scales. This work shows the important role of light-induced structural deformations within the inorganic sublattice in elucidating the unique optoelectronic functionality exhibited by hybrid perovskites and provides new understanding of hot carrier-lattice interactions, which fundamentally determine solar cell efficiencies

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

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

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

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