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Influence of the Cu(In,Ga)Se2 thickness and Ga grading on solar cell performance
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Materials Science.
2003 (English)In: Progress in Photovoltaics: Research and Applications, ISSN 1062-7995, Vol. 11, no 2, 77-88 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2003. Vol. 11, no 2, 77-88 p.
URN: urn:nbn:se:uu:diva-92778OAI: oai:DiVA.org:uu-92778DiVA: diva2:166071
Available from: 2005-03-24 Created: 2005-03-24 Last updated: 2009-04-29Bibliographically approved
In thesis
1. On Generation and Recombination in Cu(In,Ga)Se2 Thin-Film Solar Cells
Open this publication in new window or tab >>On Generation and Recombination in Cu(In,Ga)Se2 Thin-Film Solar Cells
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The solar cell technology based on Cu(In,Ga)Se2 (CIGS) thin-films provides a promising route to cost competitive solar electricity. The standard device structure is ZnO:Al/ZnO/CdS/CIGS/Mo films on a glass substrate, where the first three layers are n-type semiconductors with wide bandgaps, forming a pn-junction with the p-type CIGS absorber layer; the Mo layer serves as a back contact. This thesis deals with analysis of the generation and recombination of electron-hole pairs throughout the device. These processes determine the maximum output power: generation limits the current; recombination limits the voltage.

The generation is calculated with an optical model based on complex refractive indices determined for the individual layers. The main features of the optical response of the solar cell can be reproduced with a specular model neglecting scattering. A model including ideally Lambertian scattering at the front and back surface of the CIGS absorber layer is introduced to investigate the possibility to maintain a high current generation with thin absorber layers. The result highlights the relatively poor optical performance of the Mo back contact. TiN and ZrN are explored as alternatives, and improved optical performance is experimentally demonstrated for both materials.

The recombination analysis emphasizes that, in general, more than one recombination path of comparable magnitude are operative in parallel. For cells with absorber bandgap increasing from 1.0 eV (CuInSe2) to 1.7 eV (CuGaSe2), a relative increase of interface recombination is found. When these cells are subject to accelerated ageing, degradation is smallest for intermediate bandgaps; an explanation involving different sensitivity to decreased absorber band bending and activation of grain boundaries is suggested. The optical gain with ZrN back contacts is counteracted by increased back contact recombination and contact resistance, but an intermediate layer of MoSe2 is shown to alleviate these problems, allowing for an overall improved efficiency.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. x+112 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 28
Electronics, solar energy conversion, solar cells, Cu(In, Ga)Se2, device modelling, optical properties, electron-hole generation, light trapping, electron-hole recombination, Elektronik
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
urn:nbn:se:uu:diva-5721 (URN)91-554-6191-3 (ISBN)
Public defence
2005-04-15, Polhem, The Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Available from: 2005-03-24 Created: 2005-03-24 Last updated: 2013-07-30Bibliographically approved

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