Low Intensity Conduction States in FeS₂: Implications for Absorption, Open-Circuit Voltage and Surface Recombination
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Lazić_2013_J._Phys.__Condens._Matter_25_465801.pdf
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Author(s)
Armiento, R
Chan, M K Y
Lazic, Predrag
Herbert, Francis William
Sun, Ruoshi
Chakraborty, Rupak
Buonassisi, Anthony
Yildiz, Bilge
Ceder, Gerbrand
Hartman, Katy
Date Issued
October 2013
Journal
Journal of Physics: Condensed Matter
Publisher
IOP Publishing
Citation
Lazić, P et al. “Low Intensity Conduction States in FeS₂: Implications for Absorption, Open-Circuit Voltage and Surface Recombination.” Journal of Physics: Condensed Matter 25, 46 (October 2013): 465801 © 2013 IOP Publishing Ltd
Version
Final published version
Abstract
Pyrite (FeS₂), being a promising material for future solar technologies, has so far exhibited in experiments an open-circuit voltage (OCV) of around 0.2 V, which is much lower than the frequently quoted 'accepted' value for the fundamental bandgap of ∼0.95 eV. Absorption experiments show large subgap absorption, commonly attributed to defects or structural disorder. However, computations using density functional theory with a semi-local functional predict that the bottom of the conduction band consists of a very low intensity sulfur p-band that may be easily overlooked in experiments because of the high intensity onset that appears 0.5 eV higher in energy. The intensity of absorption into the sulfur p-band is found to be of the same magnitude as contributions from defects and disorder. Our findings suggest the need to re-examine the value of the fundamental bandgap of pyrite presently in use in the literature. If the contribution from the p-band has so far been overlooked, the substantially lowered bandgap would partly explain the discrepancy with the OCV. Furthermore, we show that more states appear on the surface within the low energy sulfur p-band, which suggests a mechanism of thermalization into those states that would further prevent extracting electrons at higher energy levels through the surface. Finally, we speculate on whether misidentified states at the conduction band onset may be present in other materials.
MIT Department
Massachusetts Institute of Technology. Department of Materials Science and Engineering
Massachusetts Institute of Technology. Department of Mechanical Engineering
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
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DOI of Published Version
https://doi.org/10.1088/0953-8984/25/46/465801
