Microscopic investigation of molecule dipole reordering in organometal halide perovskites

• Applicant: Dr. Michael Schnedler
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 447951695

Organic-inorganic halide perovskites show remarkable quantum efficiencies in photovoltaic applications like solar cells, outperforming conventional silicon-based devices. To elucidate the physical origins of these uniquely high conversion efficiencies, exceptionally intense research activity arose in the condensed matter society, recently. However, till now, no research project addresses the microscopic investigation of molecule dipole (re)ordering and its impact on the electronic structure in these materials. This fact gains importance when considering that the collaborating research groups of both PIs discovered quite recently that the intercalated molecule dipoles in halide perovskites reorder and thus form highly conductive channels for charge carrier transport under illumination. Hence, atomically-resolved investigations of the molecule dipole (re)order under operation conditions, i.e. under illumination, could be the key for a physical understanding of the exceptionally high quantum efficiencies of organometal halide perovskites. Therefore, in this proposal we plan a microscopic investigation of the molecule (re)ordering and dynamics in organometal halide perovskites under actual operation conditions of solar cells, i.e. illumination. The objective is to map the dipole orientation under various conditions, to identify stable dipole ordering phases, order-disorder transitions, and dipole dynamics, to elucidate their effect on the fundamental electric properties of the material. In particular the effect of dipole orientation on the local potential, electronic properties, and carrier transport will be elucidated.In order to tackle these objectives with atomically-resolved insight, we will use low- and variable temperature cross-sectional scanning tunneling microscopy (XSTM) and spectroscopy (XSTS). Investigations are aided by laser irradiation for generating excited carriers within the perovskites and thus for analyzing the impact of molecule dipole reordering on the electric properties under illumination. These measurements are supported by off-axis electron holography to unravel the electronic properties of domain walls and interfaces. Further complementary techniques available for this project are (scanning) transmission electron microscopy, energy-dispersive X-ray spectroscopy, and secondary ion mass spectrometry. The experimental methods are supported by self-consistent simulations for quantifying molecule dipole induced polarization fields.The results can be expected to give a comprehensive physical understanding of the importance of molecule dipole order on the charge carrier dynamics and high photovoltaic performance in halide perovskites.

• DFG Programme: Research Grants
• International Connection: Taiwan
• Partner Organisation: National Science and Technology Council (NSTC)
• Cooperation Partner: Professorin Dr. Ya-Ping Chiu