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Growth and characterization of ZnO-based buffer layers for CIGS solar cells
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
2010 (English)In: Proceedings of the SPIE - The International Society for Optical Engineering: Oxide-based Materials and Devices / [ed] Teherani FH, Look DC, Litton CW, Rogers DJ, BELLINGHAM, WA, USA: SPIE-INT SOC OPTICAL ENGINEERING , 2010, 76030D-1-76030D-9 p.Conference paper, Published paper (Refereed)
Abstract [en]

ZnO-based compounds are of interest as buffer layers in Cu(In,Ga)Se2 (CIGS) solar cells, due to the ability to change the electrical and optical properties of ZnO by addition of other elements. The device structure of a CIGS solar cell is; soda-lime glass/Mo/CIGS/buffer layer/ZnO/ZnO:Al. This contribution treats growth and characterization of Zn1-xMgxO and Zn(O,S) on glass substrates and as buffer layers in CIGS solar cell devices. The ZnO-based compounds are grown by atomic layer deposition at deposition temperatures below 200 °C using metal-organic precursors.

Place, publisher, year, edition, pages
BELLINGHAM, WA, USA: SPIE-INT SOC OPTICAL ENGINEERING , 2010. 76030D-1-76030D-9 p.
Series
Proceedings of SPIE-The International Society for Optical Engineering, ISSN 0277-786X ; 7603
Keyword [en]
ZnO, buffer layer, Cu(In, Ga)Se-2, atomic layer deposition
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-133169DOI: 10.1117/12.846351ISI: 000284035700007ISBN: 978-0-8194-7999-0 (print)OAI: oai:DiVA.org:uu-133169DiVA: diva2:360274
Conference
Conference on Oxide-based Materials and Devices San Francisco, CA, JAN 24-27, 2010
Available from: 2010-11-02 Created: 2010-11-02 Last updated: 2016-04-18Bibliographically approved
In thesis
1. Cadmium Free Buffer Layers and the Influence of their Material Properties on the Performance of Cu(In,Ga)Se2 Solar Cells
Open this publication in new window or tab >>Cadmium Free Buffer Layers and the Influence of their Material Properties on the Performance of Cu(In,Ga)Se2 Solar Cells
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

CdS is conventionally used as a buffer layer in Cu(In,Ga)Se2, CIGS, solar cells. The aim of this thesis is to substitute CdS with cadmium-free, more transparent and environmentally benign alternative buffer layers and to analyze how the material properties of alternative layers affect the solar cell performance. The alternative buffer layers have been deposited using Atomic Layer Deposition, ALD. A theoretical explanation for the success of CdS is that its conduction band, Ec, forms a small positive offset with that of CIGS.

In one of the studies in this thesis the theory is tested experimentally by changing both the Ec position of the CIGS and of Zn(O,S) buffer layers through changing their gallium and sulfur contents respectively. Surprisingly, the top performing solar cells for all gallium contents have Zn(O,S) buffer layers with the same sulfur content and properties in spite of predicted unfavorable Ec offsets. An explanation is proposed based on observed non-homogenous composition in the buffer layer.

This thesis also shows that the solar cell performance is strongly related to the resistivity of alternative buffer layers made of (Zn,Mg)O. A tentative explanation is that a high resistivity reduces the influence of shunt paths at the buffer layer/absorber interface. For devices in operation however, it seems beneficial to induce persistent photoconductivity, by light soaking, which can reduce the effective Ec barrier at the interface and thereby improve the fill factor of the solar cells.

Zn-Sn-O is introduced as a new buffer layer in this thesis. The initial studies show that solar cells with Zn-Sn-O buffer layers have comparable performance to the CdS reference devices.

While an intrinsic ZnO layer is required for a high reproducibility and performance of solar cells with CdS buffer layers it is shown in this thesis that it can be thinned if Zn(O,S) or omitted if (Zn,Mg)O buffer layers are used instead. As a result, a top conversion efficiency of 18.1 % was achieved with an (Zn,Mg)O buffer layer, a record for a cadmium and sulfur free CIGS solar cell.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 75 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 787
Keyword
Cu(In, Ga)Se2, Solar cells, Thin film, Buffer layer, Window layer, ZnO, Zn(O, S), (Zn, Mg)O, Zn-Sn-O
National Category
Condensed Matter Physics
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-133112 (URN)978-91-554-7944-2 (ISBN)
Public defence
2010-12-16, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:00 (English)
Opponent
Supervisors
Note
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 717Available from: 2010-11-25 Created: 2010-11-02 Last updated: 2011-03-21Bibliographically approved

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Törndahl, TobiasHultqvist, AdamPlatzer-Björkman, CharlotteEdoff, Marika

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