Unique microscope allows unprecedented insight in nanoscale properties of perovskite solar cells

Published on 15/12/2016

LIST scientists in collaboration with colleagues from the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland, have for the first time studied the nanoscale elemental distribution of mixed perovskites which is particularly relevant for the photovoltaic efficiency and reproducibility. The discovery was possible thanks to a unique instrument developed by LIST scientists.

The HIM-SIMS instrument, which combines a novel high-resolution Helium Ion Microscope (HIM) coupled with a Secondary Ion Mass Spectrometer (HIM-SIMS), was developed during the last few years by LIST scientists, by the Advanced Instrumentation for Ion Nano- Analytics (AINA) research group belonging to LIST’s Materials Research and Technology (MRT) department within the framework of a major collaboration between LIST and Carl Zeiss.

While the conventional Zeiss Helium Ion Microscope provides morphological images with sub-nm resolution, the unique combination with SIMS allows in addition for high-sensitivity chemical imaging of surfaces with lateral resolution down to 10 nm, a factor of 5 improvement with respect to the best commercially available SIMS instrument. Furthermore, LIST developed correlative methodologies allowing the morphological and chemical data to be combined in a single image.

Joining their forces and using the HIM-SIMS instrument, the scientists from LIST and EPFL were able to make significant progress and to gain unprecedented insights into the nanoscale properties of high-efficiency perovskite solar cells.

Perovskite photovoltaics (PVs) appear in the list of the “Top 10 Emerging Technologies of 2016”, promising to be a major player in the near future carbon-free energy landscape, an inexpensive alternative to silicon solar panels. The material consists of hybrid organic and inorganic units, made out of Carbon, Nitrogen, Hydrogen, a metal (e.g. lead) and Halogens (e.g. Iodide and/or Bromide), forming a 3D crystal-lattice structure.

Usually, perovskites are deposited as thin films on a surface and self-organise into crystals that can then be used for efficient solar cells. However, limited information is available about their nanoscale distribution of the different elements after the self-organization of the material –which is vital to optimise perovskite photovoltaics.

These results of the study will help to improve the manufacturing of perovskite solar cells in the future and a better understanding of the nanoscale perovskite composition.

The work is published in the prestigious Journal of the American Chemical Society under the name of "Intrinsic Halide Segregation at Nanometer Scale Determines the High Efficiency of Mixed Cation/Mixed Halide Perovskite Solar Cells". (Link: http://pubs.acs.org/doi/abs/10.1021/jacs.6b10049)