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Handick E, Reinhard P, Alsmeier JH, Köhler L, Pianezzi F, Krause S, Gorgoi M, Ikenaga E, Koch N, Wilks RG, Buecheler S, Tiwari AN, Bär M. Potassium Postdeposition Treatment-Induced Band Gap Widening at Cu(In,Ga)Se₂ Surfaces--Reason for Performance Leap? ACS APPLIED MATERIALS & INTERFACES 2015; 7:27414-27420. [PMID: 26633568 DOI: 10.1021/acsami.5b09231] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Direct and inverse photoemission were used to study the impact of alkali fluoride postdeposition treatments on the chemical and electronic surface structure of Cu(In,Ga)Se2 (CIGSe) thin films used for high-efficiency flexible solar cells. We find a large surface band gap (E(g)(Surf), up to 2.52 eV) for a NaF/KF-postdeposition treated (PDT) absorber significantly increases compared to the CIGSe bulk band gap and to the Eg(Surf) of 1.61 eV found for an absorber treated with NaF only. Both the valence band maximum (VBM) and the conduction band minimum shift away from the Fermi level. Depth-dependent photoemission measurements reveal that the VBM decreases with increasing surface sensitivity for both samples; this effect is more pronounced for the NaF/KF-PDT CIGSe sample. The observed electronic structure changes can be linked to the recent breakthroughs in CIGSe device efficiencies.
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Affiliation(s)
- Evelyn Handick
- Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Hahn-Meitner-Platz 1, 14109 Berlin, Germany
| | - Patrick Reinhard
- Laboratory of Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology , Ueberlandstrasse 129, CH-8600 Duebendorf, Zurich, Switzerland
| | - Jan-Hendrik Alsmeier
- Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Hahn-Meitner-Platz 1, 14109 Berlin, Germany
| | - Leonard Köhler
- Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Hahn-Meitner-Platz 1, 14109 Berlin, Germany
| | - Fabian Pianezzi
- Laboratory of Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology , Ueberlandstrasse 129, CH-8600 Duebendorf, Zurich, Switzerland
| | - Stefan Krause
- Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Hahn-Meitner-Platz 1, 14109 Berlin, Germany
- Institut für Physik and IRIS Adlershof, Humboldt-Universität zu Berlin , Brook-Taylor-Straße 6, 12489 Berlin, Germany
| | | | - Eiji Ikenaga
- SPring-8/JASRI, 1-1-1 Koto, Sayo-cho, Hyogo 679-5198, Japan
| | - Norbert Koch
- Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Hahn-Meitner-Platz 1, 14109 Berlin, Germany
- Institut für Physik and IRIS Adlershof, Humboldt-Universität zu Berlin , Brook-Taylor-Straße 6, 12489 Berlin, Germany
| | - Regan G Wilks
- Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Hahn-Meitner-Platz 1, 14109 Berlin, Germany
| | - Stephan Buecheler
- Laboratory of Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology , Ueberlandstrasse 129, CH-8600 Duebendorf, Zurich, Switzerland
| | - Ayodhya N Tiwari
- Laboratory of Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology , Ueberlandstrasse 129, CH-8600 Duebendorf, Zurich, Switzerland
| | - Marcus Bär
- Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Hahn-Meitner-Platz 1, 14109 Berlin, Germany
- Institut für Physik und Chemie, Brandenburgische Technische Universität Cottbus-Senftenberg , Platz der deutschen Einheit 1, 03046 Cottbus, Brandenburg, Germany
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