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

Abstract

World-record power conversion efficiencies for Cu(In,Ga)Se{sub 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 μm, which is ∼4 times larger than the film thickness. Thus, 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:
; ; ; ;
Publication Date:
OSTI Identifier:
22597665
Resource Type:
Journal Article
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 120; Journal Issue: 6; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-8979
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CARRIER LIFETIME; CARRIERS; CHARGE CARRIERS; COMPUTERIZED SIMULATION; COPPER SELENIDE SOLAR CELLS; DEPOSITION; DIFFUSION; DIFFUSION LENGTH; EFFICIENCY; ELECTRIC POTENTIAL; FILL FACTORS; FILMS; FLUCTUATIONS; INDIUM SELENIDE SOLAR CELLS; PHOTOLUMINESCENCE; POTASSIUM FLUORIDES; SPECTROSCOPY; THICKNESS; TIME RESOLUTION

Citation Formats

Jensen, S. A., E-mail: Soren.Jensen@nrel.gov, E-mail: Darius.Kuciauskas@nrel.gov, Glynn, S., Kanevce, A., Dippo, P., Li, J. V., Levi, D. H., and Kuciauskas, D., E-mail: Soren.Jensen@nrel.gov, E-mail: Darius.Kuciauskas@nrel.gov. Beneficial effect of post-deposition treatment in high-efficiency Cu(In,Ga)Se{sub 2} solar cells through reduced potential fluctuations. United States: N. p., 2016. Web. doi:10.1063/1.4960344.
Jensen, S. A., E-mail: Soren.Jensen@nrel.gov, E-mail: Darius.Kuciauskas@nrel.gov, Glynn, S., Kanevce, A., Dippo, P., Li, J. V., Levi, D. H., & Kuciauskas, D., E-mail: Soren.Jensen@nrel.gov, E-mail: Darius.Kuciauskas@nrel.gov. Beneficial effect of post-deposition treatment in high-efficiency Cu(In,Ga)Se{sub 2} solar cells through reduced potential fluctuations. United States. doi:10.1063/1.4960344.
Jensen, S. A., E-mail: Soren.Jensen@nrel.gov, E-mail: Darius.Kuciauskas@nrel.gov, Glynn, S., Kanevce, A., Dippo, P., Li, J. V., Levi, D. H., and Kuciauskas, D., E-mail: Soren.Jensen@nrel.gov, E-mail: Darius.Kuciauskas@nrel.gov. Sun . "Beneficial effect of post-deposition treatment in high-efficiency Cu(In,Ga)Se{sub 2} solar cells through reduced potential fluctuations". United States. doi:10.1063/1.4960344.
@article{osti_22597665,
title = {Beneficial effect of post-deposition treatment in high-efficiency Cu(In,Ga)Se{sub 2} solar cells through reduced potential fluctuations},
author = {Jensen, S. A., E-mail: Soren.Jensen@nrel.gov, E-mail: Darius.Kuciauskas@nrel.gov and Glynn, S. and Kanevce, A. and Dippo, P. and Li, J. V. and Levi, D. H. and Kuciauskas, D., E-mail: Soren.Jensen@nrel.gov, E-mail: Darius.Kuciauskas@nrel.gov},
abstractNote = {World-record power conversion efficiencies for Cu(In,Ga)Se{sub 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 μm, which is ∼4 times larger than the film thickness. Thus, 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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