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Title: Wide Band Gap CuGa(S,Se)2 Thin Films on Transparent Conductive Fluorinated Tin Oxide Substrates as Photocathode Candidates for Tandem Water Splitting Devices

Abstract

Theaim of this report was to explore the potential of CuGa(S,Se)2 thin films as wide-EG top cell absorbers for photoelectrochemical (PEC) water splitting. A synthesis was developed on fluorinated tin oxide (FTO) photocathodes by converting copper-rich co-evaporated CuGaSe2 into CuGa(S,Se)2 via a post-deposition annealing. We found it necessary to first anneal CuGaSe2 at low-temperature in sulfur then at high-temperature in nitrogen to preserve the transparency and conductivity of the FTO. Using this two-step synthesis, we fabricated a 1.72eV CuGa(S,Se)2 photocathode with a saturation current density and photocurrent onset potential of 10mA/cm2 and -0.20V vs. RHE, respectively. Yet we found that the PEC performance and sub-EG transmittance, worsened with increasing copper content. Using flatband potential measurements and the Gerischer model, we show that divergences in PEC performance of CuGa(S,Se)2 photocathodes can be explained by differences in conduction band minimums and Fermi levels. We also explain that sub-EG transmittance is likely hampered by a defect band 100-400 meV below EC. Additional external quantum efficiency measurements of a high-efficiency 1.1 eV Cu(In,Ga)Se2 photovoltaic driver, while shaded by the CuGa(S,Se)2 photocathode, yielded a short-circuit current density of 4.14 mA/cm2 revealing that CuGa(S,Se)2 reflects promise as a top cell for PEC water splitting.

Authors:
ORCiD logo [1];  [1];  [1]
  1. Univ. of Hawaii, Honolulu, HI (United States)
Publication Date:
Research Org.:
Univ. of Hawaii, Honolulu, HI (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Transportation Office. Fuel Cell Technologies Office
OSTI Identifier:
1570461
Grant/Contract Number:  
EE0006670
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 122; Journal Issue: 26; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

DeAngelis, Alexander D., Horsley, Kimberly, and Gaillard, Nicolas. Wide Band Gap CuGa(S,Se)2 Thin Films on Transparent Conductive Fluorinated Tin Oxide Substrates as Photocathode Candidates for Tandem Water Splitting Devices. United States: N. p., 2018. Web. doi:10.1021/acs.jpcc.8b02915.
DeAngelis, Alexander D., Horsley, Kimberly, & Gaillard, Nicolas. Wide Band Gap CuGa(S,Se)2 Thin Films on Transparent Conductive Fluorinated Tin Oxide Substrates as Photocathode Candidates for Tandem Water Splitting Devices. United States. https://doi.org/10.1021/acs.jpcc.8b02915
DeAngelis, Alexander D., Horsley, Kimberly, and Gaillard, Nicolas. Sun . "Wide Band Gap CuGa(S,Se)2 Thin Films on Transparent Conductive Fluorinated Tin Oxide Substrates as Photocathode Candidates for Tandem Water Splitting Devices". United States. https://doi.org/10.1021/acs.jpcc.8b02915. https://www.osti.gov/servlets/purl/1570461.
@article{osti_1570461,
title = {Wide Band Gap CuGa(S,Se)2 Thin Films on Transparent Conductive Fluorinated Tin Oxide Substrates as Photocathode Candidates for Tandem Water Splitting Devices},
author = {DeAngelis, Alexander D. and Horsley, Kimberly and Gaillard, Nicolas},
abstractNote = {Theaim of this report was to explore the potential of CuGa(S,Se)2 thin films as wide-EG top cell absorbers for photoelectrochemical (PEC) water splitting. A synthesis was developed on fluorinated tin oxide (FTO) photocathodes by converting copper-rich co-evaporated CuGaSe2 into CuGa(S,Se)2 via a post-deposition annealing. We found it necessary to first anneal CuGaSe2 at low-temperature in sulfur then at high-temperature in nitrogen to preserve the transparency and conductivity of the FTO. Using this two-step synthesis, we fabricated a 1.72eV CuGa(S,Se)2 photocathode with a saturation current density and photocurrent onset potential of 10mA/cm2 and -0.20V vs. RHE, respectively. Yet we found that the PEC performance and sub-EG transmittance, worsened with increasing copper content. Using flatband potential measurements and the Gerischer model, we show that divergences in PEC performance of CuGa(S,Se)2 photocathodes can be explained by differences in conduction band minimums and Fermi levels. We also explain that sub-EG transmittance is likely hampered by a defect band 100-400 meV below EC. Additional external quantum efficiency measurements of a high-efficiency 1.1 eV Cu(In,Ga)Se2 photovoltaic driver, while shaded by the CuGa(S,Se)2 photocathode, yielded a short-circuit current density of 4.14 mA/cm2 revealing that CuGa(S,Se)2 reflects promise as a top cell for PEC water splitting.},
doi = {10.1021/acs.jpcc.8b02915},
journal = {Journal of Physical Chemistry. C},
number = 26,
volume = 122,
place = {United States},
year = {2018},
month = {6}
}

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Table 1 Table 1: Samples discussed in this study and their relevant experimental parameters

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