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RAPID Cu(In,Ga)Se2 GROWTH USING "END POINT DETECTION"
2000 (English)In: Conference Record of the Twenty-Eighth IEEE Photovoltaic Specialist Conference-2000, 2000, 509-512 p.Conference paper, Published paper (Other academic)
Abstract [en]

Thin film Cu(ln,Ga)Se2, (GIGS) is grown using a two stage co-evaporation process where all of the Cu is evaporated in the first stage. Near the end of the second stage, a Cu-rich to Cu-poor transition occurs, where the power delivered to the substrate heater in order to sustain a constant substrate temperature, changes as a result of a change in the radiative behavior of the GIGS film. The output power signal is shown to respond quickly to, and be characteristic of the film composition near the transition. Using this signal to monitor the deposition process results in excellent control of the final Cu content, even when the evaporation rates are poorly known and poorly controlled. High quality devices result, even at high evaporation rates. Solar cells with efficiencies close to 15 % have been produced from GIGS deposition, times below 15 minutes and are only marginally better for deposition times of up to 45 minutes, and this at constant substrate temperatures of 500 degrees C.

Place, publisher, year, edition, pages
2000. 509-512 p.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-169797DOI: 10.1109/PVSC.2000.915883ISBN: 0-7803-5772-8 (print)OAI: oai:DiVA.org:uu-169797DiVA: diva2:508226
Conference
Photovoltaic Specialists Conference, 2000
Available from: 2012-03-07 Created: 2012-03-06 Last updated: 2012-04-19
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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