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Title: Beneficial effect of post-deposition treatment in high-efficiency Cu(In,Ga)Se 2 solar cells through reduced potential fluctuations

Abstract

World-record power conversion efficiencies for Cu(In,Ga)Se 2 (CIGS) solar cells have been achieved via a post-deposition treatment with alkaline metals, which increases the open-circuit voltage and fill factor. We explore the role of the potassium fluoride (KF) post-deposition treatment in CIGS by employing energy- and time-resolved photoluminescence spectroscopy and electrical characterization combined with numerical modeling. The bulk carrier lifetime is found to increase with post-deposition treatment from 255 ns to 388 ns, which is the longest charge carrier lifetime reported for CIGS, and within ~40% of the radiative limit. We find evidence that the post-deposition treatment causes a decrease in the electronic potential fluctuations. These potential fluctuations have previously been shown to reduce the open-circuit voltage and the device efficiency in CIGS. Additionally, numerical simulations based on the measured carrier lifetimes and mobilities show a diffusion length of ~10 um, which is ~4 times larger than the film thickness. Furthermore, carrier collection in the bulk is not a limiting factor for device efficiency. By considering differences in doping, bandgap, and potential fluctuations, we present a possible explanation for the voltage difference between KF-treated and untreated samples.

Authors:
 [1];  [1];  [1];  [1];  [2]; ORCiD logo [1]; ORCiD logo [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States); Texas State Univ., San Marcos, TX (United States)
Publication Date:
Research Org.:
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
OSTI Identifier:
1310173
Alternate Identifier(s):
OSTI ID: 1294677
Report Number(s):
NREL/JA-5J00-65144
Journal ID: ISSN 0021-8979; JAPIAU
Grant/Contract Number:  
AC36-08GO28308
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 120; Journal Issue: 6; Journal ID: ISSN 0021-8979
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CIGS; PDT; KF; TRPL; potential fluctuations; numerical methods; converters; chemical elements; polycrystalline material; electrical characterization; transition metal chalcogenides; band gap; time-resolved photoluminescence spectroscopy; thin films; electrical properties and parameters

Citation Formats

Jensen, Soren A., Glynn, Stephen, Kanevce, Ana, Dippo, Pat, Li, Jian V., Levi, Dean H., and Kuciauskas, Darius. Beneficial effect of post-deposition treatment in high-efficiency Cu(In,Ga)Se2 solar cells through reduced potential fluctuations. United States: N. p., 2016. Web. doi:10.1063/1.4960344.
Jensen, Soren A., Glynn, Stephen, Kanevce, Ana, Dippo, Pat, Li, Jian V., Levi, Dean H., & Kuciauskas, Darius. Beneficial effect of post-deposition treatment in high-efficiency Cu(In,Ga)Se2 solar cells through reduced potential fluctuations. United States. doi:10.1063/1.4960344.
Jensen, Soren A., Glynn, Stephen, Kanevce, Ana, Dippo, Pat, Li, Jian V., Levi, Dean H., and Kuciauskas, Darius. Fri . "Beneficial effect of post-deposition treatment in high-efficiency Cu(In,Ga)Se2 solar cells through reduced potential fluctuations". United States. doi:10.1063/1.4960344. https://www.osti.gov/servlets/purl/1310173.
@article{osti_1310173,
title = {Beneficial effect of post-deposition treatment in high-efficiency Cu(In,Ga)Se2 solar cells through reduced potential fluctuations},
author = {Jensen, Soren A. and Glynn, Stephen and Kanevce, Ana and Dippo, Pat and Li, Jian V. and Levi, Dean H. and Kuciauskas, Darius},
abstractNote = {World-record power conversion efficiencies for Cu(In,Ga)Se2 (CIGS) solar cells have been achieved via a post-deposition treatment with alkaline metals, which increases the open-circuit voltage and fill factor. We explore the role of the potassium fluoride (KF) post-deposition treatment in CIGS by employing energy- and time-resolved photoluminescence spectroscopy and electrical characterization combined with numerical modeling. The bulk carrier lifetime is found to increase with post-deposition treatment from 255 ns to 388 ns, which is the longest charge carrier lifetime reported for CIGS, and within ~40% of the radiative limit. We find evidence that the post-deposition treatment causes a decrease in the electronic potential fluctuations. These potential fluctuations have previously been shown to reduce the open-circuit voltage and the device efficiency in CIGS. Additionally, numerical simulations based on the measured carrier lifetimes and mobilities show a diffusion length of ~10 um, which is ~4 times larger than the film thickness. Furthermore, carrier collection in the bulk is not a limiting factor for device efficiency. By considering differences in doping, bandgap, and potential fluctuations, we present a possible explanation for the voltage difference between KF-treated and untreated samples.},
doi = {10.1063/1.4960344},
journal = {Journal of Applied Physics},
issn = {0021-8979},
number = 6,
volume = 120,
place = {United States},
year = {2016},
month = {8}
}

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