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Evaluation of Zn-Sn-O buffer layers for CuIn0.5Ga0.5Se2 solar cells
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. (Solar Cells)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. (Solar Cells)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. (Solar Cells)
2011 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 19, no 4, 478-481 p.Article in journal (Refereed) Published
Abstract [en]

Thin Zn-Sn-O films are evaluated as new buffer layer material for Cu(In,Ga)Se-2-based solar cell devices. A maximum conversion efficiency of 13.8% (V-oc = 691 mV, J(sc)(QE) = 27.9 mA/cm(2), and FF = 71.6%) is reached for a solar cell using the Zn-Sn-O buffer layer which is comparable to the efficiency of 13.5% (V-oc - 706 mV, J(sc)(QE) - 26.3 mA/cm(2), and FF = 72.9%) for a cell using the standard reference CdS buffer layer. The open circuit voltage (V-oc) and the fill factor (FF) are found to increase with increasing tin content until an optimum in both parameters is reached for Sn/(Zn+Sn) values around 0.3-0.4.

Place, publisher, year, edition, pages
2011. Vol. 19, no 4, 478-481 p.
Keyword [en]
Zn-Sn-O, Cu(In, Ga)Se2, buffer layer, atomic layer deposition
National Category
Condensed Matter Physics Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics; Engineering Science with specialization in Electronics
Identifiers
URN: urn:nbn:se:uu:diva-133098DOI: 10.1002/pip.1039ISI: 000290481100011OAI: oai:DiVA.org:uu-133098DiVA: diva2:360098
Available from: 2010-11-02 Created: 2010-11-02 Last updated: 2017-12-12Bibliographically 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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Hultqvist, AdamEdoff, MarikaTörndahl, Tobias

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