title: Formation of a K-In-Se Surface Species by NaF/KF Postdeposition Treatment of Cu(In,Ga)Se2Thin-Film Solar Cell Absorbers.
abstract: A NaF/KF postdeposition treatment (PDT) has recently been employed to achieve new record efficiencies of Cu(In,Ga)Se2(CIGSe) thin film solar cells. We have used a combination of depth-dependent soft and hard X-ray photoelectron spectroscopy as well as soft X-ray absorption and emission spectroscopy to gain detailed insight into the chemical structure of the CIGSe surface and how it is changed by different PDTs. Alkali-free CIGSe, NaF-PDT CIGSe, and NaF/KF-PDT CIGSe absorbers grown by low-temperature coevaporation have been interrogated. We find that the alkali-free and NaF-PDT CIGSe surfaces both display the well-known Cu-poor CIGSe chemical surface structure. The NaF/KF-PDT, however, leads to the formation of bilayer structure in which a K-In-Se species covers the CIGSe compound that in composition is identical to the chalcopyrite structure of the alkali-free and NaF-PDT absorber.
authors.affiliation: Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB) , Hahn-Meitner Platz 1, 14109 Berlin, Germany.
authors.forename: Evelyn
authors.identifier: http://orcid.org/0000-0002-9773-9981
authors.initials: E
authors.lastname: Handick
authors.affiliation: Laboratory of Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials and Science and Technology , Überlandstraße 129, 8600 Dübendorf, Switzerland.
authors.forename: Patrick
authors.identifier: http://orcid.org/0000-0001-5105-9967
authors.initials: P
authors.lastname: Reinhard
authors.affiliation: Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB) , Hahn-Meitner Platz 1, 14109 Berlin, Germany.|Energy Materials In-Situ Laboratory Berlin, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Albert-Einstein-Straße 15, 12489 Berlin, Germany.
authors.forename: Regan G
authors.initials: RG
authors.lastname: Wilks
authors.affiliation: Laboratory of Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials and Science and Technology , Überlandstraße 129, 8600 Dübendorf, Switzerland.
authors.forename: Fabian
authors.initials: F
authors.lastname: Pianezzi
authors.affiliation: Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB) , Hahn-Meitner Platz 1, 14109 Berlin, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Kunze
authors.affiliation: Institute for Photon Science and Synchrotron Radiation (IPS) and Institute for Chemical Technology and Polymer Chemistry (ITCP), Karlsruhe Institute of Technology (KIT) , Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Dagmar
authors.initials: D
authors.lastname: Kreikemeyer-Lorenzo
authors.affiliation: Institute for Photon Science and Synchrotron Radiation (IPS) and Institute for Chemical Technology and Polymer Chemistry (ITCP), Karlsruhe Institute of Technology (KIT) , Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.|Department of Chemistry and Biochemistry, University of Nevada, Las Vegas (UNLV) , 4505 S. Maryland Parkway, Las Vegas, Nevada 89154-4003, United States.
authors.forename: Lothar
authors.initials: L
authors.lastname: Weinhardt
authors.affiliation: Department of Chemistry and Biochemistry, University of Nevada, Las Vegas (UNLV) , 4505 S. Maryland Parkway, Las Vegas, Nevada 89154-4003, United States.
authors.forename: Monika
authors.initials: M
authors.lastname: Blum
authors.affiliation: Advanced Light Source (ALS), Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Wanli
authors.initials: W
authors.lastname: Yang
authors.affiliation: Energy Materials In-Situ Laboratory Berlin, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Albert-Einstein-Straße 15, 12489 Berlin, Germany.|Institute for Nanospectroscopy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Albert-Einstein-Straße 15, 12489 Berlin, Germany.
authors.forename: Mihaela
authors.initials: M
authors.lastname: Gorgoi
authors.affiliation: SPring-8/JASRI , 1-1-1 Koto, Sayo-cho, Hyogo 679-5198, Japan.
authors.forename: Eiji
authors.initials: E
authors.lastname: Ikenaga
authors.affiliation: MANA/Nano-Electronics Materials Unit, National Institute for Materials Science , 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Dominic
authors.initials: D
authors.lastname: Gerlach
authors.affiliation: Synchrotron X-ray Station at SPring-8 , NIMS. 1-1-1 Kouto, Sayo-cho, Hyogo 679-5148, Japan.|Quantum Beam Unit , NIMS, 1-2-1, Sengen, Tsukuba, Ibaraki 305-0047, Japan.
authors.forename: Shigenori
authors.initials: S
authors.lastname: Ueda
authors.affiliation: MANA/Nano-Electronics Materials Unit, National Institute for Materials Science , 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Yamashita
authors.affiliation: MANA/Nano-Electronics Materials Unit, National Institute for Materials Science , 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Toyohiro
authors.initials: T
authors.lastname: Chikyow
authors.affiliation: Institute for Photon Science and Synchrotron Radiation (IPS) and Institute for Chemical Technology and Polymer Chemistry (ITCP), Karlsruhe Institute of Technology (KIT) , Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.|Department of Chemistry and Biochemistry, University of Nevada, Las Vegas (UNLV) , 4505 S. Maryland Parkway, Las Vegas, Nevada 89154-4003, United States.
authors.forename: Clemens
authors.initials: C
authors.lastname: Heske
authors.affiliation: Laboratory of Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials and Science and Technology , Überlandstraße 129, 8600 Dübendorf, Switzerland.
authors.forename: Stephan
authors.initials: S
authors.lastname: Buecheler
authors.affiliation: Laboratory of Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials and Science and Technology , Überlandstraße 129, 8600 Dübendorf, Switzerland.
authors.forename: Ayodhya N
authors.initials: AN
authors.lastname: Tiwari
authors.affiliation: Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB) , Hahn-Meitner Platz 1, 14109 Berlin, Germany.|Energy Materials In-Situ Laboratory Berlin, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Albert-Einstein-Straße 15, 12489 Berlin, Germany.|Institut für Physik und Chemie, Brandenburgische Technische Universität Cottbus-Senftenberg , Platz der Deutschen Einheit 1, 03046 Cottbus, Germany.
authors.forename: Marcus
authors.initials: M
authors.lastname: Bär
keywords: X-ray spectroscopy; alkali postdeposition treatment; chalcopyrite thin-film solar cells; chemical surface structure; photoelectron spectroscopy