Poster award for MatSEC PhD student at the MRS Spring Meeting
At the MRS Spring Meeting in San Francisco, Kai Neldner was awarded for his poster contribution.
The poster contribution of Kai Neldner (HZB-Department Crystallography) was awarded a poster price of the Symposium "Thin-Film Compound Semiconductors" at the MRS Spring Meeting in San Francisco. Kai Neldner, a PhD student in the HZB Graduate School "Materials for Solar Energy Conversion" (MatSEC) has presented results on structural properties of Kesterites (Cu2ZnSnS4 - CZTS) in relation to its stoichiometry deviations.
The best performances of Kesterite-based thin film solar cells with converion efficiencies of 12.6% were obtained with an absorber material quite different from the stoichiometric compound Cu2ZnSn(S,Se)4, especially with a Cu-poor/Zn-rich composition. Because the electronic properties of a semiconductor are strongly related to its crystal structure, it is of great interest to study the nature of stoichiometry deviations systematically and to connect issues such as phase existence limits.
Kai Neldner synthesized off-stoichiometric CZTS powder samples by solid state reaction and studied the structural and chemical properties. He applied different analytical methods using also the HZB's large scale facilities BESSY II and BER II. With his obtained results he was able to prove that CZTS can accomodate deviations from stoichiometry without collapse of the kesterite type structure by the formation of certain point defects. Thus the crystal structure of CZTS can self-adapt to Cu-poor/Zn-rich and Cu-rich/Zn-poor compositions without any structural changes except in terms of the cation distribution.
- Marcel Risch has been appointed Professor at the Freie Universität BerlinMarcel Risch was appointed to a W2-S professorship in the Department of Physics at Freie Universität Berlin in August 2026. His research group has been transformed into the department 'Mechanisms of Sustainable Electrocatalysis'. Risch investigates the fundamental mechanisms of electrocatalytic reactions and, on this basis, develops knowledge- and data-driven strategies to improve electrocatalysts for the sustainable production of hydrogen, fuels and chemicals.
- BESSY II: High-resolution insights into individual biomolecules and catalystsVery small biological samples and even individual biomolecules can now be examined under near-physiological conditions with high confidence at the BESSY II infrared beamline with a newly validated and improved technique: The nanoscale infrared spectroscopy (s-SNOM) with ultra-thin silicon-based membranes. An international team demonstrated after an initial proof of concept, that high-resolution (a few tens of nanometres) nano-IR measurements reliably match expected far-field IR spectra in an aqueous environment. This methodological advance provides a solid foundation for studying biomaterials or observing catalytic processes in a liquid environment.
- New method shows how molecular switches are influenced by their neighborsResearchers at Friedrich Schiller University Jena and the Helmholtz Centre Berlin (HZB) have, for the first time, been able to directly observe how the environment surrounding a molecular switch influences its electronic structure. Molecular switches are molecules that can be switched between two states by external influences such as changes in temperature—similar to a switch with the positions »On« and »Off«. Such molecules are being investigated as potential building blocks for future data storage devices or sensor materials. Using magnetic-field-dependent terahertz spectroscopy, the researchers have now, for the first time, been able to distinguish whether neighbouring molecules in a material are in the same or different states. The results have been published in the journal »Angewandte Chemie International Edition«.