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Poster Award MRS 2015 San Francisco

The Poster with the title “Electronic Transport Studies of Hematite α-Fe2O3 Nanoparticles for Photovoltaic Application” by Jan Mock was awarded a poster award in April 2015 on the “Material Research Society (MRS) Spring Meeting & Exhibit 2015“ ( in San Francisco for the session “Photoactive Nanoparticles and Nanostructures”.

Content of the presentation is the electrical characterization of hematite (α-Fe2O3) nanoparticles, which can be applied as an absorber material in solar cells and for photo electrochemical water splitting. A significant increase of the electrical conductivity over six orders of magnitude for a layer stack of hematite nanoparticles was observed when annealed with temperatures successively increasing from 300 K up to 620 K under vacuum conditions. The strongly enhanced conductivity is an indication for a phase transition of the semi-conducting hematite to the quasi metallic magnetite (Fe3O4). For annealing temperatures above 600 K a partial phase transition was also observed by Raman spectroscopy.

We interpret the enhanced conductivity as increasing generation of transport paths, which enable the percolation by magnetite shells surrounding hematite cores. An enhancement of the conductivity due to agglomeration or sintering of the particles was excluded by scanning electron microscopy.The results indicate a continuous material conversion of hematite into magnetite for annealing temperatures as low as 400 K, which is 600 K lower than theoretically predicted. We demonstrated the high sensitivity of temperature dependent conductivity measurements to identify phase transitions for nanoparticle layers.

The characterization of metal oxides as absorber material for solar cells is one of the focus areas of the research group “Materials Characterization and Nanomaterials” headed by Prof. Dr. R. Carius.