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Title: Variations in the Chemical and Electronic Impact of Post-Deposition Treatments on Cu(In,Ga)(S,Se)2 Absorbers

Abstract

We present a comparative study that focuses on the variability of post-deposition treatments (NaF-PDT and KF-PDT) and their impact on the chemical and electronic structure of chalcopyrite thin film solar cell absorbers. For this purpose, two 'extreme' chalcopyrite absorber systems are studied: Cu(In,Ga)(S,Se)2 with industrial relevance (STION), and Cu(In,Ga)Se2 with 'research grade' properties (NREL). Samples were subjected to NaF-PDT and KF-PDT, and investigated using x-ray and ultra-violet photoelectron spectroscopy, Auger electron spectroscopy, as well as synchrotron-based soft x-ray emission spectroscopy. Considerably different alkali-induced effects are found for the two systems. In particular, we only detect a PDT-related Cu depletion on the NREL absorber surfaces (and only on those leading to high-efficiency devices). We also observe a reduction in the surface S/Se ratio for all alkali-treated STION absorbers, in addition to the presence of sulfates after the KF-PDT. After processing the PDT absorbers to fully operating cells, we find that the PDT temperature has a significant impact on the resulting device efficiencies - both the NREL and STION absorbers can result in high-efficiency and low-efficiency devices, depending on KF-PDT processing parameters. The absorbers of low-efficiency KF-PDT devices show the largest Cu surface content after PDT, causing the valence band maximum tomore » be closer to the Fermi energy, thus possibly leading to less efficient charge-carrier separation and/or enhanced recombination at the interface. Finally, we find varying degrees of Na, K, and/or F residuals on the different absorber surfaces after PDT, indicating a potential 'hidden' parameter in employing PDTs for improved solar cell performance.« less

Authors:
ORCiD logo [1];  [2];  [1]; ORCiD logo [3];  [1];  [4];  [5];  [4]
  1. Univ. of Nevada, Las Vegas, NV (United States)
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
  4. Univ. of Nevada, Las Vegas, NV (United States); Karlsruhe Inst. of Technology (KIT) (Germany)
  5. STION Corp., San Jose, CA (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office; USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division
OSTI Identifier:
1594942
Alternate Identifier(s):
OSTI ID: 1576486
Report Number(s):
NREL/JA-5K00-75198
Journal ID: ISSN 2574-0962; ark:/13030/qt9965x7nn
Grant/Contract Number:  
AC02-05CH11231; AC36-08GO28308
Resource Type:
Accepted Manuscript
Journal Name:
ACS Applied Energy Materials
Additional Journal Information:
Journal Volume: 2; Journal Issue: 2; Journal ID: ISSN 2574-0962
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; alkali post-deposition treatment; chalcopyrite thin-film solar cell; photoelectron spectroscopy; X-ray emission spectroscopy; potassium fluoride; sodium fluoride; x-ray emission spectroscopy

Citation Formats

Mezher, Michelle, Mansfield, Lorelle M., Horsley, Kimberly, Yang, Wanli, Blum, Monika, Weinhardt, Lothar, Ramanathan, Kannan, and Heske, Clemens. Variations in the Chemical and Electronic Impact of Post-Deposition Treatments on Cu(In,Ga)(S,Se)2 Absorbers. United States: N. p., 2019. Web. https://doi.org/10.1021/acsaem.9b01565.
Mezher, Michelle, Mansfield, Lorelle M., Horsley, Kimberly, Yang, Wanli, Blum, Monika, Weinhardt, Lothar, Ramanathan, Kannan, & Heske, Clemens. Variations in the Chemical and Electronic Impact of Post-Deposition Treatments on Cu(In,Ga)(S,Se)2 Absorbers. United States. https://doi.org/10.1021/acsaem.9b01565
Mezher, Michelle, Mansfield, Lorelle M., Horsley, Kimberly, Yang, Wanli, Blum, Monika, Weinhardt, Lothar, Ramanathan, Kannan, and Heske, Clemens. Thu . "Variations in the Chemical and Electronic Impact of Post-Deposition Treatments on Cu(In,Ga)(S,Se)2 Absorbers". United States. https://doi.org/10.1021/acsaem.9b01565. https://www.osti.gov/servlets/purl/1594942.
@article{osti_1594942,
title = {Variations in the Chemical and Electronic Impact of Post-Deposition Treatments on Cu(In,Ga)(S,Se)2 Absorbers},
author = {Mezher, Michelle and Mansfield, Lorelle M. and Horsley, Kimberly and Yang, Wanli and Blum, Monika and Weinhardt, Lothar and Ramanathan, Kannan and Heske, Clemens},
abstractNote = {We present a comparative study that focuses on the variability of post-deposition treatments (NaF-PDT and KF-PDT) and their impact on the chemical and electronic structure of chalcopyrite thin film solar cell absorbers. For this purpose, two 'extreme' chalcopyrite absorber systems are studied: Cu(In,Ga)(S,Se)2 with industrial relevance (STION), and Cu(In,Ga)Se2 with 'research grade' properties (NREL). Samples were subjected to NaF-PDT and KF-PDT, and investigated using x-ray and ultra-violet photoelectron spectroscopy, Auger electron spectroscopy, as well as synchrotron-based soft x-ray emission spectroscopy. Considerably different alkali-induced effects are found for the two systems. In particular, we only detect a PDT-related Cu depletion on the NREL absorber surfaces (and only on those leading to high-efficiency devices). We also observe a reduction in the surface S/Se ratio for all alkali-treated STION absorbers, in addition to the presence of sulfates after the KF-PDT. After processing the PDT absorbers to fully operating cells, we find that the PDT temperature has a significant impact on the resulting device efficiencies - both the NREL and STION absorbers can result in high-efficiency and low-efficiency devices, depending on KF-PDT processing parameters. The absorbers of low-efficiency KF-PDT devices show the largest Cu surface content after PDT, causing the valence band maximum to be closer to the Fermi energy, thus possibly leading to less efficient charge-carrier separation and/or enhanced recombination at the interface. Finally, we find varying degrees of Na, K, and/or F residuals on the different absorber surfaces after PDT, indicating a potential 'hidden' parameter in employing PDTs for improved solar cell performance.},
doi = {10.1021/acsaem.9b01565},
journal = {ACS Applied Energy Materials},
number = 2,
volume = 2,
place = {United States},
year = {2019},
month = {11}
}

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