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  • 1. Campa, Andrej
    et al.
    Cernivec, Gregor
    Schleussner, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Krc, Janez
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Topic, Marko
    Potential of optical improvements of the back contact in thin Cu(In,Ga)Se2 solar cells2007In: Proceedings of the 22nd European Photovoltaic Solar Energy Conference, Milano, 2007 : 3CO.9.2, 2007Conference paper (Refereed)
  • 2.
    Edoff, Marika
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Schleussner, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Wallin, Erik
    Solibro Research AB.
    Lundberg, Olle
    Solibro Research AB.
    Technological and economical aspects on the influence of reduced Cu(In,Ga)Se2 thickness and Ga grading for co-evaporated Cu(In,Ga)Se2 modules2011In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 21, p. 7530-7533Article in journal (Refereed)
    Abstract [en]

    Reducing the Cu(In,Ga)Se2 (CIGS) thickness is one way of improving the throughput and capacity in existing production, provided that the efficiency can be kept at a high level. Our experimental results from an in-line co-evaporation process show that it is possible to produce CIGS solar cells with good efficiency at a CIGS thickness of less than 1 µm. An efficiency of 14.4% was obtained for an evaporation time of 8 min and a resulting CIGS thickness of only 0.8 [mu]m. The quantum efficiency measurements show only a minor reduction of the collection in the infrared region that can be related to losses caused by reduced absorption. Passivation of the back contact has been found to be important for thin devices and one way of obtaining good back contact properties, or to reduce the impact of back contact recombination is to use an increased Ga content near the back contact. We have found that Ga grading is feasible also in the three stage process, i.e. a Ga-rich layer near the back contact from stage one is to a high degree retained also after stages two and three. In this paper we discuss the implication of efficiency reduction for the economy of the production and how high efficiency loss that can be tolerated, provided that the output is doubled at equal production cost for the CIGS layer.

  • 3.
    Edoff, Marika
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Viard, Nicolas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Wätjen, Jörn Timo
    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, Experimental Physics.
    Schleussner, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Westin, Per-Oskar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    Sputtering of highly adhesive Mo back contact layers for Cu(In,Ga)Se2 solar cells2009Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    In this work the sputter process for back contact Mo layers was adjusted to increase the adhesive strength of the Mo layers to the glass substrate, while keeping a high deposition rate and high conductivity. Mo layers were fabricated using DC magnetron sputtering in an in-line sputtering system. The adhesive strength was tested with ultrasonic agitation. The combination of good adhesion and high deposition rate was obtained by using a double layer, where the thickness of the first adhesion layer was varied between 25 and 100 nm and sputtered at 15 mTorr, whereas the second bulk layer was varied between 300 and 600 nm and sputtered at 6 mTorr. Solar cells were prepared for all different thicknesses of the adhesive layer and showed similar performance.

  • 4.
    Malmström, Jonas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Materials Science.
    Schleussner, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Stolt, Lars
    Enhanced back reflectance and quantum efficiency in Cu(In,Ga)Se2 thin film solar cells with a ZrN back reflector2004In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 85, no 13, p. 2634-2636Article in journal (Refereed)
    Abstract [en]

    A reactively sputtered ZrN reflector layer on top of the conventional Mo back contact yields enhanced absorber/back contact reflectance in Cu(In,Ga)Se2 thin film solar cells. Improved long wavelength quantum efficiency is demonstrated with a ZrN reflector at a Cu(In,Ga)Se2 thickness of 0.5 µm. The optical gain with respect to a standard Mo back contact is initially offset by increased back contact recombination and contact resistance, but these electronic losses can be suppressed by Ga grading of the absorber or by inclusion of a contact layer of MoSe$_2$. This allows for a significantly improved power conversion efficiency of devices with sub-micron Cu(In,Ga)Se2 thickness

  • 5. Powalla, Michael
    et al.
    Kessler, Friedrich
    Hariskos, Dimitrios
    Voorwinden, Georg
    Tiwari, Ayodhya N
    Brémaud, David
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Schleussner, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Stolt, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Dimmler, Bernhard
    Wächter, Rolf
    Klenk, Reiner
    Pistor, Paul
    Abou-Ras, Daniel
    Schock, Hans-Werner
    Kerrec, Olivier
    Grand, Pierre-Philippe
    Lincot, Daniel
    Naghavi, Negar
    Pérez-Rodrigues, Alejandro
    Auvray, Stéphane
    Highly productive manufacturing of CIS-based large-area modules2007Conference paper (Refereed)
  • 6.
    Schleussner, Sebastian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Törndahl, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Reactively sputtered ZrN for application as reflecting back contact in Cu(In,Ga)Se-2 solar cells2009In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 517, no 18, p. 5548-5552Article in journal (Refereed)
    Abstract [en]

    We investigate reactively sputtered films of zirconium nitride, ZrN, for use as highly reflecting back contacts in Cu(In,Ga)Se2 (CIGS) devices with sub-micrometer absorbers. We identify the nitrogen flow and the sputter current as the decisive parameters for the composition, and demonstrate a method for determining the nitrogen flow at which the transition from metallic to compound sputtering mode occurs for a given current. Films prepared at this working point consist of stoichiometric ZrN with a low resistivity, a high reflectance for red and infrared light, and have a fairly high sputter rate. Calculations show that the reflectance at the ZrN/CIGS interface is significantly superior to that at the standard Mo/CIGS interface.

    Download full text (pdf)
    fulltext
  • 7.
    Schleussner, Sebastian Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    ZrN Back-Contact Reflectors and Ga Gradients in Cu(In,Ga)Se2 Solar Cells2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Solar cells constitute the most direct way of converting solar energy to electricity, and thin-film solar-cell technologies have lately been growing in importance, allowing the fabrication of less expensive modules that nonetheless have good power-conversion efficiencies. This thesis focuses on solar cells based on Cu(In,Ga)Se2, which is the thin-film technology that has shown the highest conversion efficiency to date, reaching 20.3 % on the laboratory scale. Solar modules still have some way to go to become entirely competitive with existing energy technologies, and there are two possible paths to this goal: Firstly, reducing their manufacturing costs, for instance by minimizing the material usage per module and/or by increasing the throughput of a given factory; and secondly, increasing the power output per module in other words, the module efficiency. The subject matters of this thesis are related to those two approaches.

    The first issue investigated is the possibility for reducing the thickness of the Cu(In,Ga)Se2 layer and compensating for lost absorption by using a ZrN back reflector. ZrN layers are fabricated by reactive sputtering and I present a method for tuning the sputtering parameters so as to obtain a back reflector with good optical, electrical and mechanical properties. The reflector layer cannot be used directly in CIGS devices, but relatively good devices can be achieved with a precursor providing a homogeneous supply of Na, the addition of a very thin sacrificial Mo layer that allows the formation of a film of MoSe2 passivating the back contact, and optionally a Ga gradient that further keeps electrons away from the back contact.

    The second field of study concerns the three-stage CIGS coevaporation process, which is widely used in research labs around the world and has yielded small-area cells with highest efficiencies, but has not yet made it to large scale production. My focus lies on the development and the effect of gradients in the [Ga]/[In+Ga] ratio. On the one hand, I investigate 'intrinsic' gradients (ones that form autonomously during the evaporation), and present a formation model based on the differing diffusivity of Ga and In atoms in CIGS and on the development along the quasi-binary tie line between (In,Ga)2Se3 and Cu2Se. On the other hand, I determine how the process should be designed in order to preserve 'extrinsic' gradients due to interdiffusion. Lastly, I examine the electrical effects of Ga-enhancement at the back and at the front of the absorber and of In-enhancement at the front. Over a wide range, In-rich top layers prove to have no or a weakly beneficial effect, while Ga-rich top regions pose a high risk to have a devastating effect on device performance.

    List of papers
    1.
    The record could not be found. The reason may be that the record is no longer available or you may have typed in a wrong id in the address field.
    2. Reactively sputtered ZrN for application as reflecting back contact in Cu(In,Ga)Se-2 solar cells
    Open this publication in new window or tab >>Reactively sputtered ZrN for application as reflecting back contact in Cu(In,Ga)Se-2 solar cells
    2009 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 517, no 18, p. 5548-5552Article in journal (Refereed) Published
    Abstract [en]

    We investigate reactively sputtered films of zirconium nitride, ZrN, for use as highly reflecting back contacts in Cu(In,Ga)Se2 (CIGS) devices with sub-micrometer absorbers. We identify the nitrogen flow and the sputter current as the decisive parameters for the composition, and demonstrate a method for determining the nitrogen flow at which the transition from metallic to compound sputtering mode occurs for a given current. Films prepared at this working point consist of stoichiometric ZrN with a low resistivity, a high reflectance for red and infrared light, and have a fairly high sputter rate. Calculations show that the reflectance at the ZrN/CIGS interface is significantly superior to that at the standard Mo/CIGS interface.

    Place, publisher, year, edition, pages
    Elsevier, 2009
    Keywords
    ZrN, Reactive DC magnetron sputtering, Optical properties, CIGS
    National Category
    Engineering and Technology
    Research subject
    Materials Science
    Identifiers
    urn:nbn:se:uu:diva-102584 (URN)10.1016/j.tsf.2009.03.196 (DOI)000267182700028 ()
    Note
    Correction in: Thin Solid Films, 2010, vol. 518, issue 10, p. 2924, doi: 10.1016/j.tsf.2009.06.023 Available from: 2011-11-23 Created: 2009-05-08 Last updated: 2017-12-13Bibliographically approved
    3. Effect of gallium grading in Cu(In,Ga)Se2 solar-cell absorbers produced by multi-stage coevaporation
    Open this publication in new window or tab >>Effect of gallium grading in Cu(In,Ga)Se2 solar-cell absorbers produced by multi-stage coevaporation
    Show others...
    2011 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 95, no 2, p. 721-726Article in journal (Refereed) Published
    Abstract [en]

    We investigate Cu(In,Ga)Se2 thin films grown in multi-stage coevaporation processes and solar cells fabricated from such absorbers. Despite some interdiffusion during film growth, Ga/(Ga+In) gradients defined via evaporation-profile variations in the process are to a good part retained in the finished film. This indicates that the bandgap can be engineered in this type of process by varying the evaporation profiles, and consequently also that unintended profile variations should be noted and avoided. With front-side gradients the topmost part of many grains seems to be affected by a higher density of lattice defects due to the strong change of gallium content under copper-poor growth conditions. Electrically, both back-side gradients and moderate front-side gradients are shown to yield an improvement of device efficiency. If a front-side gradient is too wide, though, it causes strong voltage-dependent collection and the fill factor is severely reduced.

    Keywords
    CIGS, Coevaporation, Multi-stage process, Three-stage process, Gradients
    National Category
    Physical Sciences Engineering and Technology
    Research subject
    Engineering Science with specialization in Electronics; Engineering Science with specialization in Materials Science
    Identifiers
    urn:nbn:se:uu:diva-132556 (URN)10.1016/j.solmat.2010.10.011 (DOI)000287006900048 ()
    Available from: 2011-11-23 Created: 2010-10-21 Last updated: 2019-04-24Bibliographically approved
    4. Technological and economical aspects on the influence of reduced Cu(In,Ga)Se2 thickness and Ga grading for co-evaporated Cu(In,Ga)Se2 modules
    Open this publication in new window or tab >>Technological and economical aspects on the influence of reduced Cu(In,Ga)Se2 thickness and Ga grading for co-evaporated Cu(In,Ga)Se2 modules
    2011 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 21, p. 7530-7533Article in journal (Refereed) Published
    Abstract [en]

    Reducing the Cu(In,Ga)Se2 (CIGS) thickness is one way of improving the throughput and capacity in existing production, provided that the efficiency can be kept at a high level. Our experimental results from an in-line co-evaporation process show that it is possible to produce CIGS solar cells with good efficiency at a CIGS thickness of less than 1 µm. An efficiency of 14.4% was obtained for an evaporation time of 8 min and a resulting CIGS thickness of only 0.8 [mu]m. The quantum efficiency measurements show only a minor reduction of the collection in the infrared region that can be related to losses caused by reduced absorption. Passivation of the back contact has been found to be important for thin devices and one way of obtaining good back contact properties, or to reduce the impact of back contact recombination is to use an increased Ga content near the back contact. We have found that Ga grading is feasible also in the three stage process, i.e. a Ga-rich layer near the back contact from stage one is to a high degree retained also after stages two and three. In this paper we discuss the implication of efficiency reduction for the economy of the production and how high efficiency loss that can be tolerated, provided that the output is doubled at equal production cost for the CIGS layer.

    Place, publisher, year, edition, pages
    Elsevier, 2011
    Keywords
    Solar cells, PV modules, CIGS, Thin absorber, Ga-grading, Cost
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Electronics
    Identifiers
    urn:nbn:se:uu:diva-151407 (URN)10.1016/j.tsf.2011.01.369 (DOI)000295347700094 ()
    Available from: 2011-04-11 Created: 2011-04-11 Last updated: 2017-12-11Bibliographically approved
    5. Surface engineering in Cu(In,Ga)Se2 solar cells
    Open this publication in new window or tab >>Surface engineering in Cu(In,Ga)Se2 solar cells
    2013 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 21, no 4, p. 561-568Article in journal (Refereed) Published
    Abstract [en]

    Surface modifications of 3-stage co-evaporated Cu(In,Ga)Se2 (CIGS) thin films are investigated by finishing the evaporation with gallium-free (CuInSe2, CIS) stages of various lengths. We find substantial interdiffusion of indium and gallium, smearing out the Ga/(Ga+In) profile so that the addition of a CIS layer merely lowers the gallium content at the surface. For the thinnest top layer, equivalent to 20 nm of pure CIS, we cannot detect any compositional difference compared to the reference device. The modification are evaluated both by electrical characterization of actual solar-cell devices and by electrical modelling, using the latest version of SCAPS-1D. The best solar-cell device from this series is obtained for the 20 nm top layer, with an efficiency of 16.3 % after anti­reflective coating. However, we observe a trend of decreasing open-circuit voltage for increasing top-layer thicknesses, and we do not find direct evidence that the lowering of the gallium concentration at the CIGS surface should generally be expected to improve the device performance. A simulated device with reduced bulk and interface defect levels achieves 20 % efficiency, but the trends concerning the CIS top layer remain the same.

    Keywords
    CIGS, CIS, interface, SIMS, XPS, electrical modelling
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Electronics
    Identifiers
    urn:nbn:se:uu:diva-151405 (URN)10.1002/pip.1229 (DOI)000319425900016 ()
    Available from: 2011-04-11 Created: 2011-04-11 Last updated: 2017-12-11Bibliographically approved
    6. Development of gallium gradients in three‐ stageCu(In,Ga)Se2 co‐evaporation processes
    Open this publication in new window or tab >>Development of gallium gradients in three‐ stageCu(In,Ga)Se2 co‐evaporation processes
    Show others...
    2012 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 20, no 3, p. 284-293Article in journal (Refereed) Published
    Abstract [en]

    We use secondary-ion mass spectrometry, X-ray diffraction and scanning electron microscopy to investigate the development over time of compositional gradients in Cu(In,Ga)Se2 thin films grown in three-stage co-evaporation processes and suggest a comprehensive model for the formation of the well-known ‘notch’ structure. The model takes into account the need for compensating Cu diffusion by movement of group-III ions in order to remain on the quasi-binary tie line and indicates that the mobilities of In and Ga ions differ. Cu diffuses towards the back in the second stage and towards the front in the third, and this is the driving force for the movement of In and Ga. The [Ga]/[In + Ga] ratio then increases in the direction of the respective Cu movement because In has a higher mobility at process conditions than has Ga. Interdiffusion of In and Ga can be considerable in the (In,Ga)2Se3 film of the first stage, but seems largely to cease in Cu(In,Ga)Se2 and shows no signs of being boosted by the presence of a Cu2Se layer.

    Place, publisher, year, edition, pages
    John Wiley & Sons, 2012
    Keywords
    CIGS, three‐stage process, gradient, SIMS
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Electronics
    Identifiers
    urn:nbn:se:uu:diva-151408 (URN)10.1002/pip.1134 (DOI)000302946900005 ()
    Available from: 2011-04-11 Created: 2011-04-11 Last updated: 2017-12-11Bibliographically approved
    Download full text (pdf)
    FULLTEXT01
  • 8.
    Schleussner, Sebastian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Pettersson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Törndahl, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Surface engineering in Cu(In,Ga)Se2 solar cells2013In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 21, no 4, p. 561-568Article in journal (Refereed)
    Abstract [en]

    Surface modifications of 3-stage co-evaporated Cu(In,Ga)Se2 (CIGS) thin films are investigated by finishing the evaporation with gallium-free (CuInSe2, CIS) stages of various lengths. We find substantial interdiffusion of indium and gallium, smearing out the Ga/(Ga+In) profile so that the addition of a CIS layer merely lowers the gallium content at the surface. For the thinnest top layer, equivalent to 20 nm of pure CIS, we cannot detect any compositional difference compared to the reference device. The modification are evaluated both by electrical characterization of actual solar-cell devices and by electrical modelling, using the latest version of SCAPS-1D. The best solar-cell device from this series is obtained for the 20 nm top layer, with an efficiency of 16.3 % after anti­reflective coating. However, we observe a trend of decreasing open-circuit voltage for increasing top-layer thicknesses, and we do not find direct evidence that the lowering of the gallium concentration at the CIGS surface should generally be expected to improve the device performance. A simulated device with reduced bulk and interface defect levels achieves 20 % efficiency, but the trends concerning the CIS top layer remain the same.

    Download full text (pdf)
    fulltext
  • 9.
    Schleussner, Sebastian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Törndahl, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Influence of the N2 gas flow on optical and structural properties of reactively sputtered ZrN films2008In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 100, no 8, p. 082016-Article in journal (Refereed)
    Abstract [en]

    We present optical and structural properties of reactively sputtered zirconium nitride (ZrN) films for application as back reflectors in Cu(In,Ga)Se2 solar cells with sub-micrometer absorbers. In this study, ZrN films were deposited by reactive DC sputtering on blank, Mo-coated and Zr-coated soda-lime glass at two different process pressures and various ratios of nitrogen mixed in the argon working gas. When characterised by x-ray diffraction (XRD), the majority of the films were found to consist of single-phase cubic ZrN. All peaks corresponding to the ZrN phase were present in the diffractograms with intensities similar to those obtained from bulk ZrN, indicating that the films were randomly oriented. No significant differences were found between films grown on different substrate types. Films sputtered with lower nitrogen partial pressures displayed a spectral optical reflectance similar to metallic Zr, while films prepared with higher N2 flows showed the pronounced Drude-like reflectance characteristic of the nitride. The best ZrN films were achieved with a process pressure of 2.5 mTorr and a N2/(Ar+N2) flow ratio of 26.5%. At a wavelength of 800 nm the reflectance of these reached 85%, as compared to a typical value of 58% in the case of molybdenum.

  • 10.
    Schleussner, Sebastian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Törndahl, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Linnarsson, Margareta
    Royal Institute of Technology, Stockholm.
    Zimmermann, Uwe
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Wätjen, Timo
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Development of gallium gradients in three‐ stageCu(In,Ga)Se2 co‐evaporation processes2012In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 20, no 3, p. 284-293Article in journal (Refereed)
    Abstract [en]

    We use secondary-ion mass spectrometry, X-ray diffraction and scanning electron microscopy to investigate the development over time of compositional gradients in Cu(In,Ga)Se2 thin films grown in three-stage co-evaporation processes and suggest a comprehensive model for the formation of the well-known ‘notch’ structure. The model takes into account the need for compensating Cu diffusion by movement of group-III ions in order to remain on the quasi-binary tie line and indicates that the mobilities of In and Ga ions differ. Cu diffuses towards the back in the second stage and towards the front in the third, and this is the driving force for the movement of In and Ga. The [Ga]/[In + Ga] ratio then increases in the direction of the respective Cu movement because In has a higher mobility at process conditions than has Ga. Interdiffusion of In and Ga can be considerable in the (In,Ga)2Se3 film of the first stage, but seems largely to cease in Cu(In,Ga)Se2 and shows no signs of being boosted by the presence of a Cu2Se layer.

    Download full text (pdf)
    fulltext
  • 11.
    Schleussner, Sebastian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zimmermann, Uwe
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Wätjen, Timo
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Effect of gallium grading in Cu(In,Ga)Se2 solar-cell absorbers produced by multi-stage coevaporation2011In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 95, no 2, p. 721-726Article in journal (Refereed)
    Abstract [en]

    We investigate Cu(In,Ga)Se2 thin films grown in multi-stage coevaporation processes and solar cells fabricated from such absorbers. Despite some interdiffusion during film growth, Ga/(Ga+In) gradients defined via evaporation-profile variations in the process are to a good part retained in the finished film. This indicates that the bandgap can be engineered in this type of process by varying the evaporation profiles, and consequently also that unintended profile variations should be noted and avoided. With front-side gradients the topmost part of many grains seems to be affected by a higher density of lattice defects due to the strong change of gallium content under copper-poor growth conditions. Electrically, both back-side gradients and moderate front-side gradients are shown to yield an improvement of device efficiency. If a front-side gradient is too wide, though, it causes strong voltage-dependent collection and the fill factor is severely reduced.

    Download full text (pdf)
    fulltext
1 - 11 of 11
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  • asciidoc
  • rtf