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Title: Low intensity conduction states in FeS 2: implications for absorption, open-circuit voltage and surface recombination

Abstract

Pyrite (FeS 2), 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 highermore » energy levels through the surface. Finally, we speculate on whether misidentified states at the conduction band onset may be present in other materials.« less

Authors:
 [1];  [2];  [1];  [3];  [1];  [4];  [1];  [3];  [5];  [1]
  1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Dept. of Materials Science and Engineering
  2. Linkoping Univ., Linkoping (Sweden). Dept. of Physics, Chemistry and Biology (IFM)
  3. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Dept. of Mechanical Engineering
  4. Argonne National Lab. (ANL), Argonne, IL (United States). Center for Nanoscale Materials
  5. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Dept. of Nuclear Science and Engineering
Publication Date:
Research Org.:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1557607
Grant/Contract Number:  
FG02-96ER45571
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physics. Condensed Matter
Additional Journal Information:
Journal Volume: 25; Journal Issue: 46; Journal ID: ISSN 0953-8984
Publisher:
IOP Publishing
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY

Citation Formats

Lazić, P., Armiento, R., Herbert, F. W., Chakraborty, R., Sun, R., Chan, M. K. Y., Hartman, K., Buonassisi, T., Yildiz, B., and Ceder, G. Low intensity conduction states in FeS2: implications for absorption, open-circuit voltage and surface recombination. United States: N. p., 2013. Web. doi:10.1088/0953-8984/25/46/465801.
Lazić, P., Armiento, R., Herbert, F. W., Chakraborty, R., Sun, R., Chan, M. K. Y., Hartman, K., Buonassisi, T., Yildiz, B., & Ceder, G. Low intensity conduction states in FeS2: implications for absorption, open-circuit voltage and surface recombination. United States. doi:10.1088/0953-8984/25/46/465801.
Lazić, P., Armiento, R., Herbert, F. W., Chakraborty, R., Sun, R., Chan, M. K. Y., Hartman, K., Buonassisi, T., Yildiz, B., and Ceder, G. Mon . "Low intensity conduction states in FeS2: implications for absorption, open-circuit voltage and surface recombination". United States. doi:10.1088/0953-8984/25/46/465801. https://www.osti.gov/servlets/purl/1557607.
@article{osti_1557607,
title = {Low intensity conduction states in FeS2: implications for absorption, open-circuit voltage and surface recombination},
author = {Lazić, P. and Armiento, R. and Herbert, F. W. and Chakraborty, R. and Sun, R. and Chan, M. K. Y. and Hartman, K. and Buonassisi, T. and Yildiz, B. and Ceder, G.},
abstractNote = {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.},
doi = {10.1088/0953-8984/25/46/465801},
journal = {Journal of Physics. Condensed Matter},
number = 46,
volume = 25,
place = {United States},
year = {2013},
month = {10}
}

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Cited by: 26 works
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