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Published on: December 5, 2015
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Low intensity conduction states in FeS2: implications for absorption, open-circuit voltage and surface recombination
P Lazić1, R Armiento, F W Herbert
1Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Summary
The fundamental bandgap of pyrite (FeS2) may be lower than previously thought due to an overlooked sulfur p-band, potentially explaining its low open-circuit voltage in solar cells.
Area of Science:
- Materials Science
- Solid-State Physics
- Computational Chemistry
Background:
- Pyrite (FeS2) is a promising material for solar technologies.
- Experimental open-circuit voltage (OCV) of pyrite is significantly lower than its accepted bandgap.
- Subgap absorption in pyrite is often attributed to defects or disorder.
Purpose of the Study:
- To investigate the discrepancy between experimental OCV and the accepted bandgap of pyrite.
- To identify the cause of subgap absorption in pyrite.
- To re-evaluate the fundamental bandgap of pyrite.
Main Methods:
- Density functional theory (DFT) computations with a semi-local functional.
- Analysis of electronic band structure and absorption spectra.
- Investigation of surface states.
Main Results:
- DFT predicts a low-intensity sulfur p-band at the conduction band edge, potentially overlooked experimentally.
- Absorption into this sulfur p-band is comparable in magnitude to defect contributions.
- Surface states are found within the low-energy sulfur p-band.
Conclusions:
- The overlooked sulfur p-band may lower the effective bandgap of pyrite, explaining the low OCV.
- Defect and disorder attributions for subgap absorption may need re-evaluation.
- Surface states within the sulfur p-band could lead to electron thermalization, hindering performance.
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