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Thermal Radiation from Co-evaporated Cu(In,Ga)Se2: End point detection and process control
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. (Solcellsgruppen)
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 [en]
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: urn:nbn:se:uu:diva-170437ISBN: 978-91-554-8306-7 (print)OAI: oai:DiVA.org:uu-170437DiVA: diva2:509276
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
List of papers
1. RAPID Cu(In,Ga)Se2 GROWTH USING "END POINT DETECTION"
Open this publication in new window or tab >>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.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-169797 (URN)10.1109/PVSC.2000.915883 (DOI)0-7803-5772-8 (ISBN)
Conference
Photovoltaic Specialists Conference, 2000
Available from: 2012-03-07 Created: 2012-03-06 Last updated: 2012-04-19
2. Analysis of CIGS Films and Devices Resulting from Different Cu-rich to Cu-poor Transitions
Open this publication in new window or tab >>Analysis of CIGS Films and Devices Resulting from Different Cu-rich to Cu-poor Transitions
2001 (English)In: Proc. 17th European Photovoltaic Solar Energy Conference, Munich, Oct, 2001Conference paper, Published paper (Refereed)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-41160 (URN)
Available from: 2007-02-27 Created: 2007-02-27 Last updated: 2012-04-19
3. Growth of Coevaporated Cu(In,Ga)Se2 - The Influence of Rate Profiles on Film Morphology
Open this publication in new window or tab >>Growth of Coevaporated Cu(In,Ga)Se2 - The Influence of Rate Profiles on Film Morphology
Show others...
2001 (English)In: Mat. Res. Soc. Symp. Proc. 668, H2.2.1-H2.2.12, 2001Conference paper, Published paper (Refereed)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-41157 (URN)
Available from: 2007-02-27 Created: 2007-02-27 Last updated: 2012-04-19
4. Growth of Cu(In,Ga)Se2 films using a Cu-poor/rich/poor sequence: substrate temperature effects
Open this publication in new window or tab >>Growth of Cu(In,Ga)Se2 films using a Cu-poor/rich/poor sequence: substrate temperature effects
2003 (English)In: Thin Solid Films, Vol. 431-432, 1-5 p.Article in journal (Refereed) Published
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-45731 (URN)
Available from: 2007-02-22 Created: 2007-02-22 Last updated: 2012-04-19
5. Cu(In,Ga)Se2 thin films grown with a Cu-poor/rich/poor sequence: Growth model and structural considerations
Open this publication in new window or tab >>Cu(In,Ga)Se2 thin films grown with a Cu-poor/rich/poor sequence: Growth model and structural considerations
Show others...
2003 (English)In: Progress in Photovoltaics: Research and Applications, Vol. 11, 319-331 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-15521 (URN)
Available from: 2008-02-18 Created: 2008-02-18 Last updated: 2012-04-19
6. Thermodynamic Simulation of the Endpoint Characteristics in a CIGS Deposition Process
Open this publication in new window or tab >>Thermodynamic Simulation of the Endpoint Characteristics in a CIGS Deposition Process
2004 (English)In: Nineteenth European Photovoltaic Solar Energy Conference: proceedings of the international conference held in Paris, France, 7-11 June 2004 / [ed] Winfried Hoffmann et al., München: WIP-Renewable Energies , 2004, 1932-1935 p.Conference paper, Published paper (Refereed)
Abstract [en]

The purpose of this investigation was to model the thermodynamic behavior of a Cu(In,Ga)Se2 sample during the growth process and especially during the conversion from copper-rich to copper-poor material in a two-step  process.  Starting  from  a  very  simple  model  of  a  directly  heated  substrate  the  model  was  refined  until  it qualitatively and quantitatively explained the features observed in the real experiment. The results can be used todetermine more accurate criteria for the endpoint detection in a real-world evaporation system.

Place, publisher, year, edition, pages
München: WIP-Renewable Energies, 2004
Keyword
Cu(In, Ga)Se2, Deposition, Simulation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-106072 (URN)9788889407028 (ISBN)
Available from: 2009-06-15 Created: 2009-06-15 Last updated: 2012-04-19Bibliographically approved
7. Two-stage growth of smooth Cu(In,Ga)Se2 films using end-point detection
Open this publication in new window or tab >>Two-stage growth of smooth Cu(In,Ga)Se2 films using end-point detection
2005 (English)In: Thin Solid Films, Vol. 480-481, 61-66 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-71250 (URN)
Available from: 2005-05-02 Created: 2005-05-02 Last updated: 2012-04-19
8. Determination of the optical constants for Cu(In,Ga)Se2 and CuxSe in the IR region
Open this publication in new window or tab >>Determination of the optical constants for Cu(In,Ga)Se2 and CuxSe in the IR region
2012 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, no 11, 115101- p.Article in journal (Refereed) Published
Abstract [en]

The complex refractive index of CuxSe and Cu(In,Ga)Se2 has been calculated from experimental data in the wavelength region from 0.3 to 20μm. For Cu(In,Ga)Se2, the imaginary part exhibits very low values in the infrared range, whereas the real part decreases gently from 3 to 2.5. The CuxSe film is found to be conducting with increasing real and imaginary parts. It is found not to follow the Drude model. Reflectance and transmittance measurements were performed on thin films grown on soda lime glass and double polished low-doped silicon as substrates. Solutions for the complex refractive index were extracted from the measurement data using an optical model for the film and substrate. A method to map all solutions for the complex refractive index was applied to select the physically correct one.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2012
Keyword
optical constants, CIGS, Cu(In, Ga)Se2, CuxSe, simulation, evaporation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Materials Science; Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-169798 (URN)10.1088/0022-3727/45/11/115101 (DOI)000301355600002 ()
Available from: 2012-03-07 Created: 2012-03-06 Last updated: 2017-12-07Bibliographically approved
9. Dynamic radiative properties of the Cu(In,Ga)Se2 layer during the co-evaporation process
Open this publication in new window or tab >>Dynamic radiative properties of the Cu(In,Ga)Se2 layer during the co-evaporation process
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
Keyword
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:nbn:se:uu:diva-125722 (URN)10.1002/pip.931 (DOI)000280004100002 ()
Available from: 2010-05-27 Created: 2010-05-27 Last updated: 2017-12-12Bibliographically approved

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Citation style
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  • modern-language-association-8th-edition
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  • en-GB
  • en-US
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  • nn-NO
  • nn-NB
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  • Other locale
More languages
Output format
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