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Solution Processed Fe2SiS4 and Fe2GeS4 Crystalline Films and Solar Cells Using These Films

Different forms of thin-film solar panels have been developed and commercialized in thelast decade by identifying materials that are both efficient absorbers of solar power and cost-effective for manufacturer and consumer. Although they operate effectively in thin-film (1-3 microns) there are both environmental and economic concerns for the cost and sustainability of the materials and processes employed in these approaches. An alternative solution was seen in pursuing sustainable PV materials composed of Earth-abundant elements such as FeS2 (iron sulfide) for the absorber layer. The high absorption coefficient of FeS2 makes the compound unique among inorganic materials allowing downsizing of the thickness of the absorber layer to lower than 0.1 μm in a solar cell. The attractiveness of this thickness is visible when compared to 1.5–3.0 μm for current thin-film technologies and over 200 μm for single-crystal Si cells. Such thin layers not only conserve material but also provide an avenue to high efficiency through efficient charge separation associated with a high internal electrical field.In order to provide a ligand-field splitting of sufficient magnitude for effective solar absorption the Fe2+ ion must be bound by at least six S atoms thus assuring a sufficiently large band gap. This generally requires Fe2+ in an octahedral site. Adding a third element with an electronegativity that favors strong covalent bonding with sulfur can stabilize such a site. From these considerations Fe2SiS4 and Fe2GeS4 have been chosen to successfully deliver the performance originally expected from FeS2.


1) Low cost and abundance of materials 2) Ability to create ultra-thin films 3) High absorption properties 4) Small band-gaps in conduction

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