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Sulfurization of thin film solar cell absorbers
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences.
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2000 In: Proceedings of the 16th European Photovoltaic Solar Energy Conference and Exhibition, 771-774 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2000. 771-774 p.
URN: urn:nbn:se:uu:diva-91399OAI: oai:DiVA.org:uu-91399DiVA: diva2:164115
Available from: 2004-02-20 Created: 2004-02-20Bibliographically approved
In thesis
1. ALD Buffer Layer Growth and Interface Formation on Cu(In,Ga)Se2 Solar Cell Absorbers
Open this publication in new window or tab >>ALD Buffer Layer Growth and Interface Formation on Cu(In,Ga)Se2 Solar Cell Absorbers
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cu(In,Ga)Se2 (CIGS) thin film solar cells contain a thin layer of CdS. To avoid toxic heavy-metal-containing waste in the module production the development of a cadmium-free buffer layer is desirable. This thesis considers alternative Cd-free buffer materials deposited by Atomic Layer Deposition (ALD). Conditions of the CIGS surface necessary for ALD growth are investigated and the heterojunction interface is characterized by band alignment studies of ZnO/CIGS and In2S3/CIGS interfaces. The thesis also includes investigations on the surface modification of the CIGS absorber by sulfurization.

According to ALD theory the growth process is limited by surface saturated reactions. The ALD growth on CIGS substrates shows nucleation failure and generally suffers from surface contaminations of the CIGS layer. The grade of growth disturbance varies for different ALD precursors. The presence of surface contaminants is related to the substrate age and sodium content. Improved growth behavior is demonstrated by different pretreatment procedures.

The alignment of the energy bands in the buffer/absorber interface is an important parameter for minimization of the losses in a solar cell. The valence band and conduction band offsets was determined by in situ X-ray and UV photoelectron spectroscopy during layer by layer formation of buffer material. The conduction band offset (ΔEc) should be small but positive for optimal solar cell electrical performance according to theory. The conduction band offset was determined for the ALD ZnO/CIGS interface (ΔEc = -0.2 eV) and the ALD In2S3/CIGS interface (ΔEc = -0.25 eV).

A high temperature process for bandgap grading and a low temperature process for surface passivation by post deposition sulfurization in H2S were investigated. It is concluded that the high temperature sulfurization of CuIn(1-x)GaxSe2 leads to phase separation when x>0. The low temperature process did not result in enhanced device performance.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 51 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 942
Electronics, thin film, Cu(In, Ga)Se2, CIGS, chalcopyrite, ALD, sulfurization, buffer layer, XPS, UPS, electron spectroscopy, band alignment, atomic layer deposition, Elektronik
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
urn:nbn:se:uu:diva-4009 (URN)91-554-5883-1 (ISBN)
Public defence
2004-03-12, Polhemssalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30 (English)
Available from: 2004-02-20 Created: 2004-02-20 Last updated: 2011-11-11Bibliographically approved

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