perovskite – Page 2 – Lightsources.org

An energy-resolution record for resonant inelastic x-ray scattering

2018/02/152018/02/21

Resonant inelastic x-ray scattering (RIXS) is a powerful technique for studying electronic excitations in a wide variety of new and complex materials, offering momentum- and energy-resolution and potentially even analysis of scattered polarization. Since its inception in the 1990s, the development of RIXS instrumentation and scientific subjects have benefited from a closely intertwined evolution; improvements in energy resolution and throughput, spurred by specific scientific cases, have in turn made new subjects of study feasible. In the continued quest for substantially improved energy resolution, a novel prototype RIXS flat-crystal spectrometer was recently tested at X-ray Science Division beamline 27-ID-B at the U.S. Department of Energy’s Advanced Photon Source (APS). The spectrometer established a new record resolution for RIXS below 10 meV, together with a promise to do even better soon.

Early RIXS work was aimed at the study of charge transfer excitations in transition metal oxides (TMO), including the high-T_c superconducting Cuprates, where electronic excitations could be observed at a few eV. As the understanding of strongly correlated electron systems progressed, orbital degrees of freedom came into focus: in many Mott insulators, transitions between the active d-orbitals, the “dd excitations”, were hot topics and could reliably be observed with the then state-of-the-art resolution of 100-200 meV. Magnetism and magnetic ordering are central questions in the study of correlated electron systems. For example, the layered perovskite Iridates showing strikingly similar magnetic exchange interactions as the Cuprates, implying that unconventional superconductivity might be found here, to the intriguing assertion that magnetic properties of honeycomb Iridates might point to a quantum spin liquid as ground state of this material, the spectrum of novel, exotic properties uncovered or anticipated promise a treasure trove of scientific discoveries. In the late 2000s, RIXS was established as a probe of magnetic excitations. However, spectral features associated with magnetic excitations (“magnons”) lie at a fraction of an eV or even in the sub-10meV regime. A significant advance in energy resolution is needed to attack such subjects with RIXS.

Figure: Schematic rendering of the new flat-crystal RIXS spectrometer.

Scientists discover material ideal for smart photovoltaic windows

2018/01/222018/01/24

Berkeley Lab researchers make thermochromic windows with perovskite solar cell

Smart windows that are transparent when it’s dark or cool but automatically darken when the sun is too bright are increasingly popular energy-saving devices. But imagine that when the window is darkened, it simultaneously produces electricity. Such a material – a photovoltaic glass that is also reversibly thermochromic – is a green technology researchers have long worked toward, and now, scientists at Lawrence Berkeley National Laboratory (Berkeley Lab) have demonstrated a way to make it work.

Researchers at Berkeley Lab, a Department of Energy (DOE) national lab, discovered that a form of perovskite, one of the hottest materials in solar research currently due to its high conversion efficiency, works surprisingly well as a stable and photoactive semiconductor material that can be reversibly switched between a transparent state and a non-transparent state, without degrading its electronic properties.

Image Credit: iStock

Perovskite solar cells: perfection not required!

2018/01/152018/01/17

Experiments at BESSY II reveal why even inhomogeneous perovskite films are highly functional

Metal-organic perovskite layers for solar cells are frequently fabricated using the spin coating technique. If you follow the simplest synthesis pathway and use industry-relevant compact substrates, the perovskite layers laid down by spin coating generally exhibit numerous holes, yet attain astonishingly high levels of efficiency. The reason that these holes do not lead to significant short circuits between the front and back contact and thus high-rate charge carrier recombination has now been discovered by a HZB team headed by Dr.-Ing. Marcus Bär in cooperation with the group headed by Prof. Henry Snaith (Oxford Univ.) at BESSY II.

>Read more on the HZB website.