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Reactive sputtering of precursors for Cu2ZnSnS4 thin film 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.
2012 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 520, no 24, p. 7093-7099Article in journal (Refereed) Published
Abstract [en]

The quaternary semiconductor Cu2ZnSnS4 (CZTS) is a possible In-free replacement for Cu(In,Ga)Se-2. Here we present reactive sputtering with the possibility to obtain homogeneous CZTS-precursors with tunable composition and a stoichiometric quantity of sulfur. The precursors can be rapidly annealed to create large grained films to be used in solar cells. The reactive sputtering process is flexible, and morphology, stress and metal and sulfur contents were varied by changing the H2S/Ar-flow ratio, pressure and substrate temperature. A process curve for the reactive sputtering from CuSn and Zn targets is presented. The Zn-target is shown to switch to compound mode earlier and faster compared to the CuSn-target. The precursors containing a stoichiometric amount of sulfur exhibit columnar grains, have a crystal structure best matching ZnS and give a broad peak, best matching CZTS, in Raman scattering. In comparing process gas flows it is shown that the sulfur content is strongly dependent on the H2S partial pressure but the total pressures compared in this study have little effect on the precursor properties. Increasing the substrate temperature changes the film composition due to the high vapor pressures of Zn, SnS and S. High substrate temperatures also give slightly denser and increasingly oriented films. The precursors are under compressive stress, which is reduced with higher deposition temperatures. (C) 2012 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
2012. Vol. 520, no 24, p. 7093-7099
Keywords [en]
Cu2ZnSnS4, Kesterite, Reactive sputtering, Process curve, Photovoltaics, X-ray diffraction
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
URN: urn:nbn:se:uu:diva-183573DOI: 10.1016/j.tsf.2012.08.002ISI: 000308691700011OAI: oai:DiVA.org:uu-183573DiVA, id: diva2:574634
Available from: 2012-12-06 Created: 2012-10-29 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Reactive sputtering and composition measurements of precursors for Cu2ZnSnS4 thin film solar cells
Open this publication in new window or tab >>Reactive sputtering and composition measurements of precursors for Cu2ZnSnS4 thin film solar cells
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Cu2ZnSnS4 (CZTS) is a thin film solar cell material that only contains abundant elements and for which promising conversion efficiencies of 9.2 % have been shown. In this thesis composition measurements and reactive sputtering of precursors for CZTS films have been studied. These precursors can be annealed to create high quality CZTS films.

Accurate control and measurement of composition are important for the synthesis process. The composition of a reference sample was determined using Rutherford backscattering spectroscopy. This sample was thereafter used to find the composition of unknown samples with x-ray fluorescence measurements. Pros and cons with this approach were discussed.

The reactive sputtering process, and the resulting thin films, from a CuSn- and a Zn-target sputtered in H2S-atmosphere were investigated and described. A process curve of the system was presented and the influence of sputtering pressure and substrate temperature were examined. The pressures tested had little influence on the film properties but the substrate temperature affected both composition and morphology, giving less Zn, Sn and S and a more oriented film with increasingly facetted surface for higher temperatures.

The precursors produced with this method are suggested to have a disordered phase with randomized cations, giving a CZTS-like response from Raman spectroscopy but a ZnS-pattern from x-ray diffraction measurements. The films have an excellent homogeneity and it is possible to achieve stoichiometric sulfur content.

The complete steps from precursors, to annealed films, to finished solar cells were investigated for three controlled compositions and three substrate temperatures. The films sputtered at room temperature cracked when annealed and thus gave shunted solar cells. For the samples sputtered at higher temperatures the trend was an increased grain size for higher copper content and increased temperature. However, no connection between this and the electrical properties of the solar cells could be found.

Place, publisher, year, edition, pages
Uppsala: Uppsala universitet, 2013. p. 44
Keywords
Cu2ZnSnS4, Kesterite, Reactive sputtering, Process curve, Photovoltaics, Composition measurments
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-208543 (URN)
Presentation
2013-06-03, Å2005, Ångströmlaboratoriet, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2013-10-16 Created: 2013-10-02 Last updated: 2018-06-20Bibliographically approved

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