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  • 1.
    Aboulfadl, Hisham
    et al.
    Chalmers Univ Technol, Dept Phys, S-41296 Gothenburg, Sweden.
    Keller, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsen, Jes K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Thuvander, Mattias
    Chalmers Univ Technol, Dept Phys, S-41296 Gothenburg, Sweden.
    Riekehr, Lars
    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.
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Microstructural Characterization of Sulfurization Effects in Cu(In,Ga)Se-2 Thin Film Solar Cells2019In: Microscopy and Microanalysis, ISSN 1431-9276, E-ISSN 1435-8115, Vol. 25, no 2, p. 532-538Article in journal (Refereed)
    Abstract [en]

    Surface sulfurization of Cu(In,Ga)Se-2 (CIGSe) absorbers is a commonly applied technique to improve the conversion efficiency of the corresponding solar cells, via increasing the bandgap towards the heterojunction. However, the resulting device performance is understood to be highly dependent on the thermodynamic stability of the chalcogenide structure at the upper region of the absorber. The present investigation provides a high-resolution chemical analysis, using energy dispersive X-ray spectrometry and laser-pulsed atom probe tomography, to determine the sulfur incorporation and chemical re-distribution in the absorber material. The post-sulfurization treatment was performed by exposing the CIGSe surface to elemental sulfur vapor for 20 min at 500 degrees C. Two distinct sulfur-rich phases were found at the surface of the absorber exhibiting a layered structure showing In-rich and Ga-rich zones, respectively. Furthermore, sulfur atoms were found to segregate at the absorber grain boundaries showing concentrations up to similar to 7 at% with traces of diffusion outwards into the grain interior.

  • 2.
    Englund, Sven
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. Uppsala universitet.
    Paneta, Valentina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Primetzhofer, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Ren, Yi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Donzel-Gargand, Olivier
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsen, Jes K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scragg, Jonathan J.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Characterization of TiN back contact interlayers with varied thickness for Cu2ZnSn(S,Se)4 thin film solar cells2017In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 639, p. 91-97Article in journal (Refereed)
    Abstract [en]

    TiN thin films have previously been used as intermediate barrier layers on Mo back contacts in CZTS(e) solar cells to suppress excessive reaction of the Mo in the annealing step. In this work, TiN films with various thickness (20, 50 and 200 nm) were prepared with reactive DC magnetron sputtering on Mo/SLG substrates and annealed, without CZTS(e) layers, in either S or Se atmospheres. The as-deposited references and the annealed samples were characterized with X-ray Photoelectron Spectroscopy, X-ray Diffraction, Time-of-Flight-Elastic Recoil Detection Analysis, Time-of-Flight-Medium-Energy Ion Scattering, Scanning Electron Microscopy and Scanning Transmission Electron Microscopy – Electron Energy Loss Spectroscopy. It was found that the as-deposited TiN layers below 50 nm show discontinuities, which could be related to the surface roughness of the Mo. Upon annealing, TiN layers dramatically reduced the formation of MoS(e)2, but did not prevent the sulfurization or selenization of Mo. The MoS(e)2 had formed near the discontinuities, both below and above the TiN layers. Another unexpected finding was that the thicker TiN layer increased the amount of Na diffused to the surface after anneal, and we suggest that this effect is related to the Na affinity of the TiN layers and the MoS(e)2 thickness.

  • 3.
    Ericson, Tove
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsson, Fredrik
    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.
    Frisk, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsen, Jes
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kosyak, Volodymyr
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Hägglund, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Li, Shuyi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zinc-Tin-Oxide Buffer Layer and Low Temperature Post Annealing Resulting in a 9.0% Efficient Cd-Free Cu2ZnSnS4 Solar Cell2017In: Solar RRL, ISSN 2367-198X, Vol. 1, no 5, article id 1700001Article in journal (Refereed)
    Abstract [en]

    Zn1−xSnxOy (ZTO) has yielded promising results as a buffer material for the full sulfur Cu2ZnSnS4 (CZTS), with efficiencies continuously surpassing its CdS-references. ZTO can be deposited by atomic layer deposition (ALD), enabling tuning of the conduction band position through the choice of metal ratio or deposition temperature. Thus, an optimization of the conduction band alignment between ZTO and CZTS can be achieved. The ZTO bandgap is generally larger than that of CdS and can therefore yield higher currents due to reduced losses in the short wavelength region. Another advantage is the possibility to omit the toxic Cd. In this study, the ALD process temperature was varied from 105 to 165 °C. Current-blocked devices were obtained at 105 °C, while the highest open-circuit voltage and device efficiency was achieved for 145 °C. The highest fill factor was seen at 165 °C. The best efficiency reached in this study was 9.0%, which, to our knowledge, is the highest efficiency reported for Cd-free full-sulfur CZTS. We also show that the effect of heat needs to be taken into account. The results indicate that part of the device improvement comes from heating the absorber, but that the benefit of using a ZTO-buffer is clear.

  • 4. Gütay, L.
    et al.
    Larsen, Jes K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Guillot, J
    Müller, M
    Bertram, F
    Christen, J
    Siebentritt, S
    MOVPE of CuGaSe< sub> 2 on GaAs in the presence of a Cu< sub> x Se secondary phase2011In: J. Cryst. Growth, Vol. 315, p. 82-Article in journal (Refereed)
  • 5. Gütay, Levent
    et al.
    Regesch, David
    Larsen, Jes K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Aida, Yasuhiro
    Depredurand, Valérie
    Redinger, Alex
    Caneva, Sabina
    Schorr, Susan
    Stephan, Christiane
    Vidal, Julien
    Feedback mechanism for the stability of the band gap of CuInSe 22012In: Physical Review B, Vol. 86, no 4, p. 045216-Article in journal (Refereed)
  • 6. Gütay, Levent
    et al.
    Regesch, David
    Larsen, Jes K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Aida, Yasuhiro
    Depredurand, Valérie
    Siebentritt, Susanne
    Influence of copper excess on the absorber quality of CuInSe22011In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 99, no 15, p. 151912-Article in journal (Refereed)
  • 7.
    Igalson, M.
    et al.
    Warsaw Univ Technol, Fac Phys, Koszykowa 79, PL-00662 Warsaw, Poland..
    Macielak, K.
    Warsaw Univ Technol, Fac Phys, Koszykowa 79, PL-00662 Warsaw, Poland..
    Urbaniak, A.
    Warsaw Univ Technol, Fac Phys, Koszykowa 79, PL-00662 Warsaw, Poland..
    Barreau, N.
    Univ Nantes, CNRS, Inst Mat Jean Rouxel IMN, 2 Rue Houssiniere,BP 32229, F-44322 Nantes 3, France..
    Larsen, Jes K
    Univ Luxembourg, Lab Photovolta, 41 Rue Brill, L-4422 Belvaux, Luxembourg..
    Excitation spectra of defect levels derived from photoinduced current transient spectroscopy - a tool for studying deep levels in Cu(In,Ga)Se2 compounds2017In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 633, no SI, p. 227-230Article in journal (Refereed)
    Abstract [en]

    Energy required for the optical excitation of carriers onto defect levels is a parameter that compliments thermal activation energy and helps to understand the electronic properties of defects under study. Here a modification of the photoinduced current transient spectroscopy (PICTS) based on phase-sensitive detection is proposed which makes possible to measure the excitation spectra of defect levels. The representative results of the excitation spectra of the epitaxial CuGaSe2 and polycrystalline Cu(In,Ga)Se2 thin films are presented. They illustrate the usefulness of the method as a tool for studying defect properties by providing data that supplement information derived from standard PICTS spectroscopy.

  • 8.
    Joel, Jonathan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Vermang, Bart
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsen, Jes
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Donzel-Gargand, Olivier
    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.
    On the assessment of CIGS surface passivation by photoluminescence2015In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 9, no 5, p. 288-292Article in journal (Refereed)
    Abstract [en]

    An optimized test structure to study rear surface passivation in Cu(In,Ga)Se-2 (CIGS) solar cells by means of photoluminescence (PL) is developed and tested. The structure - illustrated in the abstract figure - is examined from the rear side. To enable such rear PL assessment, a semi-transparent ultrathin Mo layer has been developed and integrated in place of the normal rear contact. The main advantages of this approach are (i) a simplified representation of a rear surface passivated CIGS solar cell is possible, (ii) it is possible to assess PL responses originating close to the probed rear surface, and (iii) a stable PL response as a function of air exposure time is obtained. In this work, PL measurements of such structures with and without rear surface passivation layers have been compared, and the measured improvement in PL intensity for the passivated structures is associated with enhanced CIGS rear interface properties. [GRAPHICS] Transmission electron microscope (TEM) bright field cross-section image of the rear illuminated test structure fabricated for PL characterization.

  • 9. Korhonen, E
    et al.
    Kuitunen, K
    Tuomisto, F
    Urbaniak, A
    Igalson, M
    Larsen, Jes K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Gütay, L
    Siebentritt, S
    Tomm, Y
    Vacancy defects in epitaxial thin film CuGaSe2 and CuInSe22012In: Physical Review B, Vol. 86, no 6, p. 064102-Article in journal (Refereed)
  • 10. Krysztopa, A
    et al.
    Igalson, M
    Gütay, L
    Larsen, Jes K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Aida, Y
    Defect level signatures in CuInSe< sub> 2 by photocurrent and capacitance spectroscopy2013In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 535, p. 366-370Article in journal (Refereed)
  • 11. Krysztopa, A
    et al.
    Igalson, M
    Larsen, Jes K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Aida, Y
    Gütay, L
    Siebentritt, S
    Photoinduced current transient spectroscopy of defect levels in CuInSe2 and CuGaSe2 epitaxial and polycrystalline layers2012In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, no 33, p. 335101-Article in journal (Refereed)
  • 12. Krysztopa, A
    et al.
    Igalson, M
    Zabierowski, P
    Larsen, Jes K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Aida, Y
    Siebentritt, Susanne
    Gütay, Levent
    Defect levels in CuGaSe< sub> 2 by modulated photocurrent spectroscopy2011In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 21, p. 7308-7311Article in journal (Refereed)
  • 13. Krysztopa, Adam
    et al.
    Igalson, Małgorzata
    Aida, Yasuhiro
    Larsen, Jes K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Gütay, Levent
    Siebentritt, Susanne
    Defect levels in the epitaxial and polycrystalline CuGaSe2 by photocurrent and capacitance methods2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 10, p. 103711-Article in journal (Refereed)
  • 14.
    Larsen, Jes K
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Gutay, Levent
    Siebentritt, Susanne
    Influence of secondary phase Cu x Se on the optoelectronic quality of chalcopyrite thin films2011In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 98, no 20, p. 201910-201910Article in journal (Refereed)
  • 15.
    Larsen, Jes K
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Gütay, Levent
    Aida, Yasuhiro
    Siebentritt, Susanne
    Spatial variations of optoelectronic properties in single crystalline CuGaSe< sub> 2 thin films studied by photoluminescence2011In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 21, p. 7332-7336Article in journal (Refereed)
  • 16.
    Larsen, Jes K
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Keller, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Lundberg, Olle
    Solibro Res AB, S-75651 Uppsala, Sweden..
    Jarmar, Tobias
    Solibro Res AB, S-75651 Uppsala, Sweden..
    Riekehr, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scragg, Jonathan J.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Sulfurization of Co-Evaporated Cu(In,Ga)Se-2 as a Postdeposition Treatment2018In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 8, no 2, p. 604-610Article in journal (Refereed)
    Abstract [en]

    It is investigated if the performance of Cu(In,Ga)Se-2 (CIGSe) solar cells produced by co-evaporation can be improved by surface sulfurization in a postdeposition treatment. The expected benefit would be the formation of a sulfur/selenium gradient resulting in reduced interface recombination and increased open-circuit voltage. In the conditions used here it was, however, found that the reaction of the CIGSe layer in a sulfur environment results in the formation of a CuInS2 (CIS) surface phase containing no or very little selenium and gallium. At the same time, a significant pile up of gallium was observed at the CIGSe/CIS boundary. This surface structure was formed for a wide range of annealing conditions investigated in this paper. Increasing the temperature or extending the time of the dwell stage had a similar effect on the material. The gallium enrichment and CIS surface layer widens the surface bandgap and therefore increases the open-circuit voltage. At the same time, the fill factor is reduced, since the interface layer acts as an electron barrier. Due to the balance of these effects, the conversion efficiency could not be improved.

  • 17.
    Larsen, Jes K
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsson, Fredrik
    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.
    Saini, Nishant
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Riekehr, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ren, Yi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. Midsummer AB, Elect Hojden 6, S-17543 Jarfalla, Sweden.
    Biswal, Adyasha
    KIT, Inst Photon Sci & Synchrotron Radiat IPS, Hermann von Helmholtz Pl 1, D-76344 Eggenstein Leopoldshafen, Germany;KIT, Inst Chem Technol & Polymer Chem ITCP, Engesserstr 18-20, D-76128 Karlsruhe, Germany.
    Hauschild, Dirk
    KIT, Inst Photon Sci & Synchrotron Radiat IPS, Hermann von Helmholtz Pl 1, D-76344 Eggenstein Leopoldshafen, Germany;KIT, Inst Chem Technol & Polymer Chem ITCP, Engesserstr 18-20, D-76128 Karlsruhe, Germany.
    Weinhardt, Lothar
    KIT, Inst Photon Sci & Synchrotron Radiat IPS, Hermann von Helmholtz Pl 1, D-76344 Eggenstein Leopoldshafen, Germany;KIT, Inst Chem Technol & Polymer Chem ITCP, Engesserstr 18-20, D-76128 Karlsruhe, Germany;Univ Nevada, Dept Chem & Biochem, Las Vegas UNLV, 4505 Maryland Pkwy, Las Vegas, NV 89154 USA.
    Heske, Clemens
    KIT, Inst Photon Sci & Synchrotron Radiat IPS, Hermann von Helmholtz Pl 1, D-76344 Eggenstein Leopoldshafen, Germany;KIT, Inst Chem Technol & Polymer Chem ITCP, Engesserstr 18-20, D-76128 Karlsruhe, Germany;Univ Nevada, Dept Chem & Biochem, Las Vegas UNLV, 4505 Maryland Pkwy, Las Vegas, NV 89154 USA.
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Cadmium Free Cu2ZnSnS4 Solar Cells with 9.7% Efficiency2019In: Advanced Energy Material, ISSN 1614-6832, Vol. 9, no 21, article id 1900439Article in journal (Refereed)
    Abstract [en]

    Cu2ZnSnS4(CZTS) thin-film solar cell absorbers with different bandgaps can be produced by parameter variation during thermal treatments. Here, the effects of varied annealing time in a sulfur atmosphere and an ordering treatment of the absorber are compared. Chemical changes in the surface due to ordering are examined, and a downshift of the valence band edge is observed. With the goal to obtain different band alignments, these CZTS absorbers are combined with Zn1−xSnxOy (ZTO) or CdS buffer layers to produce complete devices. A high open circuit voltage of 809 mV is obtained for an ordered CZTS absorber with CdS buffer layer, while a 9.7% device is obtained utilizing a Cd free ZTO buffer layer. The best performing devices are produced with a very rapid 1 min sulfurization, resulting in very small grains.

  • 18.
    Larsen, Jes K
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Li, Shuyi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scragg, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ren, Yi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Hägglund, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Heinemann, Marc
    Kretzschmar, Steffen
    Unold, Thomas
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Interference effects in photoluminescence spectra of Cu2ZnSnS4 and Cu(In,Ga)Se2 thin films2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, no 3, article id 035307Article in journal (Refereed)
    Abstract [en]

    Photoluminescence (PL) is commonly used for investigations of Cu2ZnSnS(e)4 [CZTS(e)] and Cu(In,Ga)Se2 (CIGS) thin film solar cells. The influence of interference effects on these measurements is, however, largely overlooked in the community. Here, it is demonstrated that PL spectra of typical CZTS absorbers on Mo/glass substrates can be heavily distorted by interference effects. One reason for the pronounced interference in CZTS is the low reabsorption of the PL emission that typically occurs below the band gap. A similar situation occurs in band gap graded CIGS where the PL emission originates predominantly from the band gap minimum located at the notch region. Based on an optical model for interference effects of PL emitted from a thin film, several approaches to reduce the fringing are identified and tested experimentally. These approaches include the use of measured reflectance data, a calculated interference function, use of high angles of incidence during PL measurements as well as the measurement of polarized light near the Brewster angle.

  • 19.
    Larsen, Jes K
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ren, Yi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ross, Nils
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. Univ Oslo, Ctr Mat Sci & Nanotechnol, Box 1126, N-0318 Oslo, Norway..
    Särhammar, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Li, Shiyu
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Surface modification through air annealing Cu2ZnSn(S,Se)4 absorbers2017In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 633, p. 118-121Article in journal (Refereed)
    Abstract [en]

    Recent studies demonstrate that air annealing can have a positive effect on the device performance of Cu2ZnSn(SxSe1-x)(4)[CZTSSe] solar cells. In this work air annealing of the selenium containing CZTSSe is compared to the pure sulfide CZTS. It is discovered that the selenium containing absorbers benefit from air annealing at higher temperatures than selenium free absorbers. The highest efficiency obtained utilizing the air annealing treatment on selenium containing absorbers is 9.7%. We find that the band gap is narrowed when air annealing, which is partially explained by increased Cu-Zn disorder. Furthermore Zn enrichment of the surface after etching is identified as a possible cause of enhanced device performance. It is additionally observed that elemental selenium present on the CZTSSe surface is reduced in the air annealing treatment. Selenium removal is another possible explanation for the enhanced performance caused by the air annealing treatment.

  • 20.
    Larsen, Jes K
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scragg, J. J.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Frisk, C
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ren, Y.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer-Björkman, C.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    CuS Cap to Prevent Decomposition of Cu2ZnSnS4 Precursors during Annealing2015Conference paper (Other academic)
    Abstract [en]

    Chemical decomposition of the CZTS surface during annealing is detrimental to device performance. Aiming to obtain more flexibility in the annealing process the surface is protected by a thin CuS cap.

  • 21.
    Larsen, Jes K
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scragg, Jonathan JS
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Frisk, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ren, Yi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Potential of CuS cap to prevent decomposition of Cu2ZnSnS4 during annealing2015In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 212, no 12, p. 2843-2849Article in journal (Refereed)
    Abstract [en]

    One of the challenges associated with processing of Cu2ZnSnS4 (CZTS) is the thermal decomposition reaction that causes loss of S and SnS from the absorber surface. To reduce the decomposition a sufficiently high SnS and S partial pressure must be supplied during annealing. The absorber surface can alternatively be protected with a thin cap. Aiming to obtain a more flexible process, CZTS precursors were capped with a thin CuS layer before annealing. The cap was subsequently removed with a KCN etch before device finishing. It was found that the cap coverage decreased during annealing, exposing a part of the absorber surface. At the same time, the initially Cu poor absorber took up Cu from the cap, ending up with a stoichiometric Cu content. Devices made from capped precursors or precursors annealed without sulfur had poor device characteristics. An increased doping density of almost one order of magnitude could be the reason for the very poor performance. CuS is therefore not a suitable cap material for CZTS. Other cap materials could be investigated to protect the CZTS absorber surface during annealing.

  • 22.
    Larsen, Jes K
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Simchi, H
    Xin, P
    Kim, K
    Shafarman, WN
    Backwall superstrate configuration for ultrathin Cu (In, Ga) Se2 solar cells2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 104, no 3, p. 033901-Article in journal (Refereed)
  • 23.
    Larsen, Jes K
    et al.
    Institute of Energy Conversion, University of Delaware, Newark, DE, 19716, USA .
    Xin, Peipei
    Shafarman, William N
    Formation of Ga2O3 barrier layer in Cu (InGa) Se2 superstrate devices with ZnO buffer layer2013In: MRS Proceedings, Vol. 1538, p. 67-72Article in journal (Refereed)
    Abstract [en]

    The junction formation when Cu(InGa)Se2 is deposited onto ZnO in a superstrate configuration (glass/window/buffer/Cu(InGa)Se2/contact) is investigated by x-ray photoelectron spectroscopy and analysis of device behavior. When Cu(InGa)Se2 is deposited on ZnO, a Ga2O3 layer is formed at the interface. Approaches to avoid the formation of this unfavorable interlayer are investigated. This includes modifications of the process to reduce the thermal load during deposition and improvement of the thermal stability of the ZnO buffer layer. It was demonstrated that both lowering of the substrate deposition temperature and deposition of the ZnO buffer layer at elevated temperature limits the Ga2O3 formation. The presence of Ga2O3 at the junction does affect the device behavior, resulting in a kink in JV curves measured under illumination. This behavior is absent in devices with limited Ga2O3 formation.

  • 24.
    Li, Shu-Yi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Hagglund, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ren, Yi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scragg, Jonathan J. S.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsen, Jes K.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Frisk, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Rudisch, Katharina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Englund, Sven
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer-Bjorkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Optical properties of reactively sputtered Cu2ZnSnS4 solar absorbers determined by spectroscopic ellipsometry and spectrophotometry2016In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 149, p. 170-178Article in journal (Refereed)
    Abstract [en]

    We have determined for the first time the device-relevant optical constants of 500 nm and 800 nm-thick Cu2ZnSnS4 absorbers, grown on bare and Mo-coated soda-lime glass (SLG), using spectroscopic ellipsometry (SE). The composition, structure, phase purity and morphology were characterized by X-ray fluorescence, X-ray photoelectron spectroscopy depth profiling, X-ray diffraction, Raman spectroscopy, scanning-electron microscopy and atomic force microscopy. For the SE analysis, carefully determined sample characteristics were utilized to build a multilayer stack optical model, in order to derive the dielectric functions and refractive indices. The SE-derived absorption coefficients from CZTS/SLG samples were compared with those derived from complementary spectrophotometry measurements and found to be in good agreement. The bandgap determined from Tauc plots was E-g=1.57 +/- 0.02 eV. The absorption coefficients just above the bandgap were found to be a few 10(4) cm(-1) and to exceed 10(5) cm(-1) at energies above similar to 2.5 eV, which is much higher than previously found. The sub-bandgap k-value was found to be k similar to 0.05 or less, suggesting that a moderate band tail is present. Separate device characterization performed on identical samples allowed us to assign device efficiencies of, respectively, 2.8% and 5.3% to the 500 nm and 800 nm-thick samples featured in this study.

  • 25.
    Li, Shu-Yi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zamulko, Sergiy
    Univ Oslo, Dept Phys, Ctr Mat Sci & Nanotechnol, NO-0316 Oslo, Norway..
    Persson, Clas
    Univ Oslo, Dept Phys, Ctr Mat Sci & Nanotechnol, NO-0316 Oslo, Norway.;Royal Inst Technol, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden..
    Ross, Nils
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. Univ Oslo, Dept Phys, Ctr Mat Sci & Nanotechnol, NO-0316 Oslo, Norway..
    Larsen, Jes K.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Optical properties of Cu2ZnSn(SxSe1-x)(4) solar absorbers: Spectroscopic ellipsometry and ab initio calculations2017In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 110, no 2, article id 021905Article in journal (Refereed)
    Abstract [en]

    Dielectric functions of Cu2ZnSn(SxSe1-x)(4) thin film absorbers with varied x were determined by spectroscopic ellipsometry and ab initio calculations. From the combination of experimental and theoretical studies, the fundamental interband transition energy E-0 (similar to 1-1.5 eV) and the next following transition energy E-1 (similar to 2-3 eV) were identified and found to blue-shift with increasing sulfur anion content, while keeping the energy separation E-1 - E-0 almost constant, similar to 1.4 eV from experiments, and 1 eV from theory. In addition, the average dielectric responses were found to decrease with sulfur anion content from both theoretical and experimental results. The Tauc optical bandgap value E-g determined on samples prepared on Mo and soda lime glass substrate showed a positive linear relationship between x and bandgap E-g. The bandgap bowing factor determined from the theoretical data is 0.09 eV. (C) 2017 Author(s).

  • 26.
    Platzer-Björkman, Charlotte
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Frisk, Christoper
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsen, Jes
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ericson, Tove
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Li, Shuyi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scragg, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Keller, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsson, Fredrik
    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.
    Reduced interface recombination in Cu2ZnSnS4 solar cells with atomic layer deposition Zn1-xSnxO buffer layers2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, no 24, article id 243904Article in journal (Refereed)
    Abstract [en]

    Cu2ZnSnS4 (CZTS) solar cells typically include a CdS buffer layer in between the CZTS and ZnO front contact. For sulfide CZTS, with a bandgap around 1.5 eV, the band alignment between CZTS and CdS is not ideal ("cliff-like"), which enhances interface recombination. In this work, we show how a Zn1-xSnxOy (ZTO) buffer layer can replace CdS, resulting in improved open circuit voltages (V-oc) for CZTS devices. The ZTO is deposited by atomic layer deposition (ALD), with a process previously developed for Cu(In,Ga)Se-2 solar cells. By varying the ALD process temperature, the position of the conduction band minimum of the ZTO is varied in relation to that of CZTS. A ZTO process at 95 degrees C is found to give higher Voc and efficiency as compared with the CdS reference devices. For a ZTO process at 120 degrees C, where the conduction band alignment is expected to be the same as for CdS, the Voc and efficiency is similar to the CdS reference. Further increase in conduction band minimum by lowering the deposition temperature to 80 degrees C shows blocking of forward current and reduced fill factor, consistent with barrier formation at the junction. Temperature-dependent current voltage analysis gives an activation energy for recombination of 1.36 eV for the best ZTO device compared with 0.98 eV for CdS. We argue that the Voc of the best ZTO devices is limited by bulk recombination, in agreement with a room temperature photoluminescence peak at around 1.3 eV for both devices, while the CdS device is limited by interface recombination.

  • 27. Regesch, David
    et al.
    Gütay, Levent
    Larsen, Jes K
    Institute of Energy Conversion, University of Delaware, Newark, Delaware 19716, USA.
    Deprédurand, Valérie
    Tanaka, Daisuke
    Aida, Yasuhiro
    Siebentritt, Susanne
    Degradation and passivation of CuInSe22012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, no 11, p. 112108-Article in journal (Refereed)
    Abstract [en]

    The degradation of CuInSe2 absorbers in ambient air is observed by the decay of the quasi-Fermi level splitting under well defined illumination with time. The decay is faster and stronger in absorbers with [Cu]/[In]<1 than in ones with a higher ratio. It can be attributed to the oxidation of the sample. Epitaxial films containing no Na show very similar trends, indicating that decay and oxidation are independent of the Na content. A standard CdS layer commonly used as buffer in solar cells, terminates the decay even over many months. Aged absorbers can be completely restored by a KCNetch.

  • 28.
    Ren, Yi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ross, Nils
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsen, Jes K.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Rudisch, Katharina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scragg, Jonathan J.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Evolution of Cu2ZnSnS4 during Non-Equilibrium Annealing with Quasi-in Situ Monitoring of Sulfur Partial Pressure2017In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 29, no 8, p. 3713-3722Article in journal (Refereed)
    Abstract [en]

    Chalcogen-based materials like Cu2ZnSnS4 (CZTS) have attracted extensive attention for applications such as photovoltaics and water splitting. However, an inability to monitor the sulfur partial pressure (P-S2) during the non equilibrium annealing process at high temperatures complicates the synthesis of CZTS with controlled optoelectronic properties. Here we demonstrate that P-S2 can be monitored by investigating the Sn-S phase transformation. We showed that P-S2 drops considerably over the annealing time, causing gradual alterations in CZTS: (i) a change in defect type and (ii) evolution of ZnS and SnxSy phases. With additional ordering treatment, we observed that the low room-temperature photoluminescence energy usually seen in CZTS can result from insufficient P-S2 during annealing. It is proven that remarkable V-oc beyond 700 mV for solar cells with nonoptimal CdS buffer can be repeatedly achieved when CZTS is prepared under a sufficiently high P-S2. An ordering treatment before CdS deposition can further improve V-oc to 783 mV.

  • 29.
    Ren, Yi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scragg, Jonathan
    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.
    Larsen, Jes
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Evolution of Na-S(-O) compounds on the Cu2ZnSnS4 absorber surface and their effects on CdS thin film growth2016In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 28, p. 18600-18607Article in journal (Refereed)
    Abstract [en]

    Formation of Na-containing surface compounds is an important phenomenon in the Cu2ZnSnS4 (CZTS) quaternary material synthesis for solar cell applications. Still, identification of these compounds and the understanding of their potential influence on buffer layer growth and device performance are scarce. In this work, we discovered that the evolution of Na-S(-O) compounds on the CZTS surface substantially affect the solution/CZTS interface during the chemical bath deposition of CdS buffer film. We showed that Na2S negatively affects the growth of CdS, and that this compound is likely to form on the CZTS surface after annealing. It was also demonstrated that the Na2S compound can be oxidized to Na2SO4 by air exposure of the annealed CZTS surface or be removed using water dipping instead of the commonly used KCN etching process, resulting in significantly better quality of the CdS layer. Lastly, 6.5% CZTS solar cells were fabricated with air exposure treatment without incorporation of the KCN etching process. This work provides new insight into the growth of the CdS/CZTS interface for solar cell applications and opens new possibilities for improving likewise Cd-free buffer materials that are grown with a similar chemical bath deposition process.

  • 30.
    Ren, Yi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scragg, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Frisk, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsen, Jes
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Li, Shuyi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Influence of the Cu2ZnSnS4 absorberthickness on thin film solar cells2015In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 212, no 12, p. 2889-2896Article in journal (Refereed)
    Abstract [en]

    In this study, we investigate the influence of absorber thickness on Cu2ZnSnS4 (CZTS) solar cells, ranging from 500 to 2000 nm, with nearly constant metallic composition. Despite the observed ZnS and SnS phases on the surface and backside of all absorber films, scanning electron microscopy, Raman scattering, and X-ray diffraction show no large variations in material quality for the different thicknesses. The open-circuit voltage (V-oc), short-circuit current and overall power conversion efficiency of the fabricated devices show an initial improvement as the absorber thickness increases but saturate when the thickness exceeds 750 nm. External quantum efficiency (EQE) measurements suggest that the current is mainly limited by collection losses. This can result from non-optimal bulk quality of the CZTS absorber (including the presence of secondary phases), which is apparently further reduced for the thinnest devices. The observed saturation of V-oc agrees with the expected influence from strong interface recombination. Finally, an effective collection depth of 750-1000 nm for the minority carriers generated in the absorber can be estimated from EQE, indicating that the proper absorber thickness for our device process is approximately 1000 nm. Performance could be improved for thicker films, if the collection depth can be increased.

  • 31.
    Ross, N.
    et al.
    Univ Oslo, N-0316 Oslo, Norway..
    Larsen, Jes K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Grini, S.
    Univ Oslo, N-0316 Oslo, Norway..
    Särhammar, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Vines, L.
    Univ Oslo, N-0316 Oslo, Norway..
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Cu2ZnSn(S,Se)4 Solar Cell Absorbers from Diffusion of Selenium into Annealed Cu2ZnSnS4 Absorbers2016In: 2016 IEEE 43rd Photovoltaic Specialists Conference (PVSC), New York: IEEE, 2016, p. 492-497Conference paper (Refereed)
    Abstract [en]

    Small grain compound-sputtered Copper Zinc Tin Sulfide (CZTS) precursors and large grain recrystallized CZTS solar cell absorbers are annealed at sub-recrystallization temperatures in selenium atmosphere to promote selenium diffusion into the CZTS films. Grazing incidence x-ray diffraction and Raman spectroscopy show the presence of two distinct sulfide and mixed sulfide/selenide phases, with the selenide-like phase more prominent at the front surface of the absorber. Only a narrow range of sulfur-to-selenium ratios is observed in the sulfide/selenide phase. Secondary ion mass spectrometry profiles show a compositional sulfur-selenium gradient for samples annealed at 450 degrees C. Scanning electron microscopy with energy dispersive X-ray spectroscopy reveals that the compositional gradient is formed by a spatial distribution of sulfide/selenide grains, embedded in the remaining sulfide absorber. Sulfur-selenium gradients within single absorber grains are not observed, indicating that the mixed sulfide/selenide phase nucleates and grows in competition with the existing sulfide phase, rather than forming by replacement of anions within existing crystals. IV and EQE measurements of devices fabricated from the selenized absorbers support this conclusion.

  • 32.
    Ross, Nils
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. Univ Oslo, Ctr Mat Sci & Nanotechnol, Dept Phys, POB 1048 Blindern, N-0316 Oslo, Norway..
    Larsen, Jes
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Grini, S.
    Univ Oslo, Ctr Mat Sci & Nanotechnol, Dept Phys, POB 1048 Blindern, N-0316 Oslo, Norway..
    Vines, L.
    Univ Oslo, Ctr Mat Sci & Nanotechnol, Dept Phys, POB 1048 Blindern, N-0316 Oslo, Norway..
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Practical limitations to selenium annealing of compound co-sputtered Cu2ZnSnS4 as a route to achieving sulfur-selenium graded solar cell absorbers2017In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 623, p. 110-115Article in journal (Refereed)
    Abstract [en]

    The suitability of selenium annealing as a technique to introduce energy band gap gradients via sulfur selenium substitution in Cu2ZnSnS4 (CZTS) films is evaluated. Compound co-sputtered CZTS precursors are annealed in selenium atmosphere at 425 degrees C, either as-deposited or after a short time sulfur pre-anneal. The films are investigated by Raman spectroscopy and X-ray diffractometry, and the spatial distribution of elemental species measured by secondary ion mass spectrometry and energy dispersive X-ray spectroscopy. Sulfur-selenium gradients are not achieved for the as-deposited precursor. Sulfur-selenium gradients are achieved in the early stages of annealing for pre-anneal samples, where Cu2ZnSn(S,Se)(4) (CZTSSe) formation is found to be correlated spatially with sodium distribution. These gradients are lost as the annealing progresses. Selenisation occurs by CZTSSe grain growth, rather than by direct substitution of selenium for sulfur. The spatial correlation of high sodium concentration with CZTSSe formation suggests that liquid phase sodium selenide facilitates selenium incorporation during recrystallisation, limiting the practicality of anion-grading of CZTSSe during the annealing step as a means of establishing a graded band gap.

  • 33.
    Scragg, Jonathan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsen, Jes
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kumar, Mukesh
    Persson, Clas
    Sendler, Jan
    Siebentritt, Susanne
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Cu–Zn disorder and band gap fluctuations in Cu2ZnSn(S,Se)4: Theoretical and experimental investigations2016In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 253, no 2, p. 247-254Article in journal (Refereed)
    Abstract [en]

    Cu2ZnSn(S,Se)4 (CZTS(e)) solar cells suffer from low-open-circuit voltages that have been blamed on the existence of band gap fluctuations, with different possible origins. In this paper, we show from both theoretical and experimental standpoints that disorder of Cu and Zn atoms is in all probability the primary cause of these fluctuations. First, quantification of Cu–Zn disorder in CZTS thin films is presented. The results indicate that disorder is prevalent in the majority of practical samples used for solar cells. Then, ab initio calculations for different arrangements and densities of disorder-induced [CuZn + ZnCu] defect pairs are presented and it is shown that spatial variations in band gap of the order of 200 meV can easily be caused by Cu–Zn disorder, which would cause large voltage losses in solar cells. Experiments using Raman spectroscopy and room temperature photoluminescence combined with in situ heat-treatments show that a shift in the energy of the dominant band-to-band recombination pathway correlates perfectly to the order-disorder transition, which clearly implicates Cu–Zn disorder as the cause of band gap fluctuations in CZTS. Our results suggest that elimination or passivation of Cu–Zn disorder could be very important for future improvements in the efficiency of CZTS(e)-based solar cells.

  • 34. Simchi, H.
    et al.
    Larsen, J. K.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Shafarman, W. N.
    Transparent Back Contacts for Superstrate (AG,CU)(IN,GA)SE2 Thin Film Solar Cells2015In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 5, no 1, p. 406-409Article in journal (Refereed)
    Abstract [en]

    Molybdenum oxide (MoO3) and tungsten oxide (WO3) are considered as transparent back contacts for (Ag,Cu)(In,Ga)Se-2 thin film solar cells. MoO3 and WO3 films were deposited by reactive RF sputtering at room temperature in an Ar/O-2 ambient on (Ag,Cu)(In,Ga) Se-2 absorber layers with various Ga/(Ga + In) and Ag/(Ag + Cu) ratios. Determination of the valence band offsets by XPS showed that Ag-alloying of absorber layer changes the energy band alignment at the absorber-back contact interface with MoO3 and WO3 contacts. This produces a primary contact with lower valence band offset compared with Cu(In,Ga) Se-2 counterparts. The effect is less significant in films with Ga > 0.5 and Ag > 0.5 (corresponding to E-g > 1.4 eV) probably due to the different nature of ordered vacancy compounds forming near the surface phases.

  • 35. Steichen, Marc
    et al.
    Larsen, Jes K
    Université du Luxembourg, Laboratoire Photovoltaïque, 41, rue du Brill, L-4422 Belvaux, Luxembourg.
    Gütay, Levent
    Siebentritt, Susanne
    Dale, PJ
    Preparation of CuGaSe 2 absorber layers for thin film solar cells by annealing of efficiently electrodeposited Cu–Ga precursor layers from ionic liquids2011In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 21, p. 7254-7258Article in journal (Refereed)
    Abstract [en]

    CuGaSe2 absorber layers were prepared on molybdenum substrates by electrochemical codeposition of copper and gallium and subsequential annealing in selenium vapour. The electrodeposition was made from a deep eutectic based ionic liquid consisting of choline chloride/urea (Reline) with a plating efficiency of over 85%. The precursor film composition is controlled by the ratio of the copper to gallium fluxes under hydrodynamic conditions and by the applied deposition potential. X-ray diffraction reveals CuGa2 alloying during the electrodeposition and CuGaSe2 formation after annealing. Photoluminescence (PL) and photocurrent spectroscopy revealed the good opto-electronic properties of the CuGaSe2 absorber films. The absorber layers have been converted to full devices with the best device achieving 4.0 % solar conversion efficiency.

  • 36.
    Suvanam, Sethu Saveda
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsen, Jes K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ross, Nils
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kosyak, Volodymyr
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Hallen, Anders
    KTH Royal Inst Technol, Sch Informat & Commun Technol, Electrum 229, S-16440 Kista, Sweden.
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Extreme radiation hard thin film CZTSSe solar cell2018In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 185, p. 16-20Article in journal (Refereed)
    Abstract [en]

    In this work, we have demonstrated the extreme radiation hardness of thin film CZTSSe solar cells. Thin film solar cells with CZTSSe, CZTS and CIGS absorber layers were irradiated with 3 MeV protons. No degradation in device parameters was observed until a displacement damage dose of 2 x 10(10) MeV/g for CZTS and CZTSSe. CIGS solar cells degraded by 13% at the same dose. For the highest proton dose both the CZTSSe and CZTS degraded by 16% while CIGS suffered from 34% degradation in efficiency. The degradation in efficiency maybe attributed to the reduction in the minority carrier lifetime due to radiation induced lattice defects. Comparisons with previously available literature show that our CZTS technology has superior radiation hardness by about two orders of magnitude compared to existing state of the art Si and GaAs technology.

1 - 36 of 36
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