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Microanalysis of post-deposition annealing of Cu(In,Ga)Se2 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.
2012 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 107, 396-402 p.Article in journal (Refereed) Published
Abstract [en]

The influence of selenium background pressure during post-deposition annealing of Cu(In,Ga)Se 2 (CIGS) is investigated. Solar cells made from samples post-annealed with selenium showed the same solar cell parameters as references without any annealing treatment. Dark JV measurements of microscopic devices with sizes of 10μm×10μm from the sample annealed with selenium showed good agreement with the corresponding macroscopic solar cells. Samples annealed without selenium showed degradation in terms of open circuit voltage and fill factor. Electron beam induced current (EBIC) imaging for these degraded solar cells revealed patches of reduced current. Microscopic JV measurements showed that the deterioration is not limited to these patches. Cross-sectional transmission electron microscopy analysis showed phase decomposition of the CIGS absorber in areas of the patches toward the back contact. We conclude that in addition to the local phase decomposition of the CIGS leading to patches in the EBIC image the anneal in vacuum without selenium background pressure also leads to other modifications of the CIGS layer influencing the interface region on a macroscopic scale.

Place, publisher, year, edition, pages
2012. Vol. 107, 396-402 p.
Keyword [en]
CIGS, Gradients, Microscopic JV-characterization, Post-deposition annealing, TEM, Three-stage process, Post deposition annealing, Electric currents, Gallium, Open circuit voltage, Selenium, Solar cells, Transmission electron microscopy, Annealing
National Category
Natural Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
URN: urn:nbn:se:uu:diva-184888DOI: 10.1016/j.solmat.2012.07.026ISI: 000311270000053OAI: oai:DiVA.org:uu-184888DiVA: diva2:570917
Available from: 2012-11-20 Created: 2012-11-15 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Microscopic Characterisation of Solar Cells: An Electron Microscopy Study of Cu(In,Ga)Se2 and Cu2ZnSn(S,Se)4 Solar Cells
Open this publication in new window or tab >>Microscopic Characterisation of Solar Cells: An Electron Microscopy Study of Cu(In,Ga)Se2 and Cu2ZnSn(S,Se)4 Solar Cells
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The sun provides us with a surplus of energy convertible to electricity using solar cells. This thesis focuses on solar cells based on chalcopyrite (CIGSe) as well as kesterite (CZTS(e)) absorber layers. These materials yield record efficiencies of 20.4 % and 11.1 %, respectively. Especially for CZTS(e), the absorber layers often do not consist of one single desired phase but can exhibit areas with deviating material properties, referred to as secondary phases. Furthermore, several material layers are required for a working solar cell, each exhibiting interfaces. Even though secondary phases and interfaces represent a very small fraction of the solar cell they can have a profound influence on the over-all electrical solar cell characteristics. As such, it is crucial to understand how secondary phases and interfaces influence the local electrical characteristics.

Characterising secondary phases and interfaces is challenging due to their small sample volume and relatively small differences in composition amongst others. This is where electronmicroscopy, especially transmission electron microscopy, offers valuable insight to material properties on the microscopic scale. The main challenge is, however, to link these material properties to the corresponding electrical characteristics of a solar cell.

This thesis uses electron beam induced current imaging and introduces a new method for JV characterisation of solar cells on the micron scale. Combining microscopic structural and electrical characterisation techniques allowed identifying and characterising local defects found in the absorber layer of CIGS solar cells after thermal treatment. Furthermore, CZTSe solar cells in this thesis exhibited a low photo-current density which is traced to the formation of a current blocking ZnSe secondary phase at the front contact interface. The electron microscopy work has contributed to an understanding of the chemical stability of CZTS and has shown the need for an optimised back contact interface in order to avoid chemical decomposition reactions and formation of detrimental secondary phases. With this additional knowledge, a comprehensive picture of the material properties from the macroscopic down to the microscopic level can be attained throughout all required material layers.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. xii + 70 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1053
Keyword
TEM, SEM, FIB, solar cell, CIGS, CZTS, Alternative buffer layers, Gallium gradients, microscopic electrical characterisation, Secondary Phases
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Physical Sciences Materials Engineering
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-199432 (URN)978-91-554-8692-1 (ISBN)
Public defence
2013-09-06, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30 (English)
Opponent
Supervisors
Available from: 2013-06-05 Created: 2013-05-04 Last updated: 2013-08-30Bibliographically approved

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Wätjen, Timo JörnZimmermann, UweEdoff, Marika

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