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Dynamic radiative properties of the Cu(In,Ga)Se2 layer during the co-evaporation process
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.
2010 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 18, no 5, 321-327 p.Article in journal (Refereed) Published
Abstract [en]

A study of the wavelength-integrated emissivity has been performed on the optical stack CuxSe/Cu(In,Ga)Se2/Mo. Thewavelength interval used in the study was 2–20 µm, which covers 95% of the radiated heat from a black body heated to500°C. Substrate temperatures around 500°C are commonly used in production of Cu(In,Ga)Se2 thin films for solar cells.The integrated emissivity was obtained from directional reflectivity measurements of experimental samples with differentthicknesses of the CuxSe layers. It was subsequently compared to the emissivity from numerical simulations based onnewly obtained values of the refractive index values for Cu(In,Ga)Se2 and Cu x Se at these wavelengths. Good agreementwas found between the measured and simulated values. At a Cu(In,Ga)Se2 thickness of 1.8 µm and a Mo thickness of 400 nm, a maximum in the integrated emissivity was found for a CuxSe thickness of 30 nm. The results are valuable inputinto understanding the dynamics of the change in emissivity between Cu-rich Cu(In,Ga)Se2 with segregated CuxSe and Cu-poor single phase Cu(In,Ga)Se2 at temperatures around 500°C. In co-evaporation of Cu(In,Ga)Se2, this emissivity changeis often monitored and used as a process control (end-point detection).

Place, publisher, year, edition, pages
Wiley , 2010. Vol. 18, no 5, 321-327 p.
Keyword [en]
CIGS, CuxSe, emissivity, segregated layer, co-evaporation, modeling
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Electronics
Identifiers
URN: urn:nbn:se:uu:diva-125722DOI: 10.1002/pip.931ISI: 000280004100002OAI: oai:DiVA.org:uu-125722DiVA: diva2:320777
Available from: 2010-05-27 Created: 2010-05-27 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Thermal Radiation from Co-evaporated Cu(In,Ga)Se2: End point detection and process control
Open this publication in new window or tab >>Thermal Radiation from Co-evaporated Cu(In,Ga)Se2: End point detection and process control
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The use of solar cells for energy production has indeed a bright future. Reduction of cost for fabrication along with increased efficiency are key features for a market boom, both achieved as a result of increased knowledge of the technology. Especially the thin film solar cell technology with absorbers made of Cu(In,Ga)Se2 (CIGS) is promising since it has proven high power conversion efficiency in combination with a true potential for low cost fabrication.

In this thesis different recipes for fabrication of the Cu(In,Ga)Se2 absorber layer have been studied. The deposition technique used has been co-evaporation from elemental sources. For all depositions the substrate has been heated to a constant temperature of 500 ºC in order for the growing absorber to form a chalcopyrite phase, necessary for the photovoltaic functionality. The selenium has been evaporated such to always be in excess during depositions whereas the metal ratio Cu/(In+Ga) has been varied according to different recipes but always to be less than one at the end of the process. In the work emphasis has been on the radiative properties of the CIGS film during growth.

The substrate heater has been temperature controlled to maintain the constant set temperature of the substrate, regardless of varying emitted power caused by changing surface emissivity. Depending on the growth conditions the emissivity of the growing film is changing, leading to a readable variation in the electrical power to the substrate heater.

Since the thermal radiation from the substrate during growth has been of central focus, this has been studied in detail. For this reason the substrate has been treated as an optical stack composed of glass/Mo/Cu(In,Ga)Se2/CuxSe which determine the thermally radiated power by its emissivity. An optical model has been adopted to simulate the emissivity of the stack. In order to use the model, the optical constants for Cu(In,Ga)Se2 and CuxSe have been derived for the wavelength interval 2 μm to 20 μm. The simulation of the emissivity of the stack during CIGS growth agreed well with what has been seen for actual growth. Features of the OP-signal could hereby be explained as a result of film thickness of Cu(In,Ga)Se2 and CuxSe respectively. This is an important knowledge for an efficient fabrication in large scale.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 66 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 909
Keyword
CIGS, Cu(InGa)Se2, thin film, solar cells, end point detection, process control, optical constants, CuxSe
National Category
Materials Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering Physical Sciences
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-170437 (URN)978-91-554-8306-7 (ISBN)
Public defence
2012-04-26, Polhemssalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30 (English)
Opponent
Supervisors
Available from: 2012-04-03 Created: 2012-03-12 Last updated: 2012-04-19Bibliographically approved

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Schöldström, JensZimmermann, UweEdoff, Marika

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