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Microanalysis of laser micro-welded interconnections in CIGS PV modules
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: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 98, 172-178 p.Article in journal (Refereed) Published
Abstract [en]

Laser micro-welding is a technique that can be used for interconnective (P2) patterning of Cu ( In , Ga ) Se 2 (CIGS) thin film solar cells after deposition of the ZnO:Al window layer. The micro-welding process transforms CIGS into a conductive compound that forms a contact between the ZnO:Al front contact and the Mo back contact. In this work we present a study on the influence of process parameters on the interconnectivity of the laser micro-weld as well as an investigation of the morphology of the micro-weld zone. We found that the current method results in an overlap of conditions where electrical connection is achieved and where Mo/glass damage is caused by laser action. Stability testing shows that interconnections processed without appreciable damage are stable. The connecting region contained metal rich zones and segregated CuxSe that we believe account for its conductivity.

Place, publisher, year, edition, pages
2012. Vol. 98, 172-178 p.
Keyword [en]
Laser micro-welding, Laser patterning, CIGS, Module technology
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Electronics
Identifiers
URN: urn:nbn:se:uu:diva-142582DOI: 10.1016/j.solmat.2011.07.032ISI: 000300536500022OAI: oai:DiVA.org:uu-142582DiVA: diva2:387704
Available from: 2011-01-14 Created: 2011-01-14 Last updated: 2017-12-11Bibliographically approved
In thesis
1. By Means of Beams: Laser Patterning and Stability in CIGS Thin Film Photovoltaics
Open this publication in new window or tab >>By Means of Beams: Laser Patterning and Stability in CIGS Thin Film Photovoltaics
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Solar irradiation is a vast and plentiful source of energy. The use of photovoltaic (PV) devices to convert solar energy directly to electrical energy is an elegant way of sustainable power generation which can be distributed or in large PV plants based on the need. Solar cells are the small building blocks of photovoltaics and when connected together they form PV modules. Thin film solar cells require significantly less energy and raw materials to be produced, as compared to the dominant Si wafer technologies. CIGS thin film solar cells are considered to be the most promising thin film alternative due to its proven high efficiency.

Most thin film PV modules utilise monolithic integration, whereby thin film patterning steps are included between film deposition steps, to create interconnection of individual cells within the layered structure. The state of the art is that CIGS thin film modules are made using one laser patterning step (P1) and two mechanical patterning steps (P2 and P3). Here we present work which successfully demonstrates the replacement of mechanical patterning by laser patterning methods. The use of laser ablation promises such advantages as increased active cell area and reduced maintenance and downtime required for regular replacement of mechanical tools.

The laser tool can also be used to transform CIGS into a conducting compound along a patterned line. We have shown that this process can be performed after all semiconductor layers are deposited using a technique we call laser micro-welding. By performing patterning at the end of the process flow P2 and P3 patterning could be performed simultaneously. Such solutions will further reduce manufacturing times and may offer increased control of semiconductor interfaces.

While showing promising performance on par with reference processes there are still open questions of importance for these novel techniques, particularly that of long term stability. Thin film modules are inherently sensitive to moisture and require reliable encapsulation. Before the techniques introduced here can be seen industrially they must have achieved proven stability. In this work we present a proof of existence of stable micro-welded interconnections.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 98 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 801
Keyword
Laser patterning, laser ablation, laser micro-welding, stability, Cu(InGa)Se2, CIGS, thin film solar cells, thin film photovoltaics, module technology, solar energy
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-143154 (URN)978-91-554-7988-6 (ISBN)
Public defence
2011-03-04, Å4001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30 (English)
Opponent
Supervisors
Note
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 731Available from: 2011-02-10 Created: 2011-01-19 Last updated: 2011-03-21Bibliographically approved
2. 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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Westin, Per-OskarWätjen, Jörn TimoZimmermann, UweEdoff, Marika

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