Hydration induced bandgap shift at pyrite-water interface

The practical application of earth abundant pyrite (FeS2) in photovoltaic devices is extremely limited by the low open-circuit voltage (OCV) (similar to 200mV) induced low efficiency (<3%). As such, finding out the causes for the low OCV and the corresponding solutions has been widely concerned. Here, we report the hydration induced bandgap shift at the pyrite-water interface, which has been ignored in previous efforts. The bandgap shift may be one of the reasons responsible for the low OCV. Using ab initio calculations, we found that, compared to the pure pyrite surface in vacuum, the bandgap of the pyrite-water interfacial system possesses blue and red shifts at the water coverage of more and less than the mono-layer, respectively. The bandgap shift of the interfacial system could be explained by the adsorption symmetry and charge transfer between water and the substrate. These results reveal that the interfacial water could change the electronic structure of the pyrite surface, suggesting that hydration could be a highly probable stratagem to tune the photovoltage properties of pyrite-based materials. Published by AIP Publishing