Twisting Under the Stroboscope – Controlling Crystal Lattices of Hybrid Solar Cell Materials with Terahertz Light

To overcome global energy challenges and fight the looming environmental crisis, researchers around the world investigate new materials for converting sunlight into electricity. Some of the most promising candidates for high-efficiency low-cost solar cell applications are based on lead halide perovskite (LHP) semiconductors. Despite record-breaking solar cell prototypes, the microscopic origin of the surprisingly excellent optoelectronic performance of this material class is still not completely understood. Now, an international team of physicists and chemists from Fritz Haber Institute of the Max Planck Society, École Polytechnique in Paris, Columbia University in New York, and the Free University in Berlin demonstrated laser-driven control of fundamental motions of the LHP atomic lattice. By applying a sudden electric field spike faster than a trillionth of a second (picosecond) in the form of a single light cycle of far-infrared Terahertz radiation, the investigators unveiled the ultrafast lattice response, which might contribute to a dynamic protection mechanism for electric charges. This precise control over the atomic twist motions will allow to create novel non-equilibrium material properties, potentially providing hints for designing the solar cell material of the future. more

Ångstrom-Depth Resolution with Chemical Specificity at the Liquid-Vapor Interface

Surfactants play an important role in every day life, for instance as major components in soaps.  Since they feature hydrophilic and hydrophobic parts in their structure, they accumulate at water interfaces with air and can there influence the rate of evaporation of the solution or the efficiency with which gas molecules are taken up by the solution, a process that is for instance important for the incorporation of carbon dioxide into the oceans. How surfactants arrange themselves at the interface of water with air is an intriguing question that has fascinated scientist for centuries, going back to Benjamin Franklin who noted the calming effect of cooking oil on the surface of water, and Agnes Pockels who did some of the first systematic experiments on the subject in the late 19th century. The question of the arrangement of surfactant molecules at the water-air interface is not easy to answer since a close look at the very skin of liquid water requires methods that hone in on the outer layers of water, where surfactant molecules are located in a layer with a thickness of only a few billionths of a meter. more

Exciton fission – one photon in, two electrons out

Photovoltaics, the conversion of light to electricity, is a key technology for sustainable energy. Since the days of Max Planck and Albert Einstein, we know that light as well as electricity are quantized, meaning they come in tiny packets called photons and electrons. In a solar cell, the energy of a single photon is transferred to a single electron of the material, but no more than one. Only a few molecular materials like pentacene are an exception, where one photon is converted to two electrons instead. This excitation doubling, which is called exciton fission, could be extremely useful for high-efficiency photovoltaics, specifically to upgrade the dominant technology based on silicon. A team of researchers at the Fritz Haber Institute of the Max Planck Society, the Technical University of Berlin, and the Julius-Maximilians-Universität of Würzburg have now deciphered the first step of this process by recording an ultrafast movie of the photon-to-electricity conversion process, resolving a decades-old debate about the mechanism of the process. more

Electrocatalysis under the atomic force microscope

A further development in atomic force microscopy now makes it possible to simultaneously image the height profile of nanometre-fine structures as well as the electric current and the frictional force at solid-liquid interfaces. A team from the Helmholtz-Zentrum Berlin (HZB) and the Fritz Haber Institute (FHI) of the Max Planck Society has succeeded in analysing electrocatalytically active materials and gaining insights that will help optimise catalysts. The method is also potentially suitable for studying processes on battery electrodes, in photocatalysis or on active biomaterials. more

The Positive Outlooks of Studying Negatively-Charged Chiral Molecules

The ability to distinguish two chiral enantiomers is an essential analytical capability for chemical industries including pharmaceutical companies, flavor/odor engineering and forensic science. A new wave of chiral optical methods have shown significant improvements in chiral sensitivity, compared to their predecessors, leading to potential analytical advantages for chiral discrimination. Researchers at the Fritz Haber Institute have integrated one of these modern methods with the study of gas-phase anions, which enable mass-selection and the use of a simple table-top laser for observation of the chiral effect. Thus, taking another step closer to realizing a robust analytical tool capable of chiral discrimination of dilute and complex, chiral mixtures. more

Discovery to lower CO<sub>2</sub> Emissions in the Industrial Sector by using Green Synthesis<br /> 

Achieving a net zero greenhouse gas balance is a major challenge facing the chemical industry. The goal can be met by reducing the energy demand of chemical processes and the sustainable use of raw materials. Researchers of the Fritz-Haber-Institute have shown that the valuable intermediates propylene and propylene oxide can be formed directly by oxidation of propane in the gas phase over nonspecific interfaces, such as sea sand, without producing significant amounts of CO2.

When machines just get it right: <br />Atomic-scale insights into defect-free growth of graphene

High-level synchrotron experiments confirm the sub-atomic precision of a machine-learning based prediction for the adsorption height of graphene at liquid metal catalysts. With such reliability, the AI-approach constitutes a powerful new tool to study the growth process of this much aspired material even under most extreme conditions.

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