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  • 1.
    Bilousov, Oleksandr V.
    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.
    Törndahl, Tobias
    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.
    Ericson, Tove
    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.
    Edoff, Marika
    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.
    ALD of phase controlled tin monosulfide thin films2017Conference paper (Refereed)
    Abstract [en]

    Tin monosulfide (SnS) is a promising semiconductor material for low-cost conversion of solar energy, playing the role of absorber layer in photovoltaic devices. SnS is, due to its high optical damping, also an excellent semiconductor candidate for the realization of ultrathin (nanoscale thickness) plasmonic solar cells [1].

    Here, we present an important step to further control and understand SnS film properties produced using low temperature ALD with Sn(acac)2 and H2S as precursors. We show that the SnS film properties vary over a rather wide range depending on substrate temperature and reaction conditions, and that this is connected to the growth of cubic (π-SnS) and orthorhombic SnS phases. The optical properties of the two polymorphs differ significantly, as demonstrated by spectroscopic ellipsometry [2].

    1. C. Hägglund, G. Zeltzer, R. Ruiz, A. Wangperawong, K. E. Roelofs, S. F. Bent, ACS Photonics 3 (3) (2016) 456–463.

    2. O. V. Bilousov, Y. Ren, T. Törndahl, O. Donzel-Gargand , T. Ericson, C. Platzer-Björkman, M. Edoff, and C. Hägglund, ACS Chemistry of Materials  29 (7) (2017) 2969–2978.

  • 2.
    Bilousov, Oleksandr V.
    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.
    Törndahl, Tobias
    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.
    Ericson, Tove
    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.
    Edoff, Marika
    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.
    Atomic Layer Deposition of Cubic and Orthorhombic Phase Tin Monosulfide2017In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 29, no 7, p. 2969-2978Article in journal (Refereed)
    Abstract [en]

    Tin monosulfide (SnS) is a promising light-absorbing material with weak environmental constraints for application in thin film solar cells. In this paper, we present low-temperature atomic layer deposition (ALD) of high-purity SnS of both cubic and orthorhombic phases. Using tin(II) 2,4-pentanedionate [Sn(acac)(2)] and hydrogen sulfide (H2S) as precursors, controlled growth of the two polymorphs is achieved. Quartz crystal microbalance measurements are used to establish saturated conditions and show that the SnS ALD is self-limiting over temperatures from at least 80 to 160 degrees C. In this temperature window, a stable mass gain of 19 ng cm(-2) cycle(-1) is observed. The SnS thin film crystal structure and morphology undergo significant changes depending on the conditions. High-resolution transmission electron microscopy and X-ray diffraction demonstrate that fully saturated growth requires a large H2S dose and results in the cubic phase. Smaller H2S doses and higher temperatures favor the orthorhombic phase. The optical properties of the two polymorphs differ significantly, as demonstrated by spectroscopic ellipsometry. The orthorhombic phase displays a wide (0.3-0.4 eV) Urbach tail in the near-infrared region, ascribed to its nanoscale structural disorder and/or to sulfur vacancy-induced gap states. In contrast, the cubic phase is smooth and void-free and shows a well-defined, direct forbidden-type bandgap of 1.64 eV.

  • 3.
    Bras, Patrice
    et al.
    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.
    Tempez, Agnes
    Niemi, Esko
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ga-grading and Solar Cell Capacitance Simulation of an industrial Cu(In,Ga)Se2 solar cell produced by an in-line vacuum, all-sputtering process2017In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 636, p. 367-374Article in journal (Refereed)
    Abstract [en]

    Cadmium-free Cu(In,Ga)Se-2 (CIGS) solar cells are fabricated on stainless steel substrate using an industrial, inline vacuum, all sputtering process. The absorber layer is deposited from compound CIGS targets and crystallized simultaneously by high temperature processing. In-depth compositional and structural characterization of the chalcopyrite material is conducted and a Solar Cell Capacitance Simulator (SCAPS) model for the complete device is set-up. Ga-grading of the absorber through the successive use of different CIGS target compositions and resulting in solar cell performance enhancement is shown. At the research and development scale, efficiency values of 15.1% and 13.2% are reported for 1 cm(2) and 225 cm(2) total area solar cells, respectively. Successful transfer to production is also demonstrated. A series of a hundred 225 cm(2) solar cells produced following an optimized process including the Ga grading studied in the present contribution average at 14.8% total area efficiency.

  • 4.
    Bras, Patrice
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. Midsummer AB, Elektronikhojden 6, SE-17143 Jarfalla, Sweden..
    Mauvy, Leo
    Midsummer AB, Elektronikhojden 6, SE-17143 Jarfalla, Sweden..
    Sterner, Jan
    Midsummer AB, Elektronikhojden 6, SE-17143 Jarfalla, Sweden..
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Uniformity assessment of a 6-inch Copper-Zinc-Tin-Sulfide solar cell sputtered from a quaternary compound target2015In: 2015 IEEE 42ND PHOTOVOLTAIC SPECIALIST CONFERENCE (PVSC), 2015Conference paper (Refereed)
    Abstract [en]

    Cu2ZnSnS4 solar cells are fabricated following an all-sputtering in line vacuum approach. 6-inch semi-square stainless steel substrates are used. A compositional and structural study of the absorber layer is conducted before and after annealing to assess the uniformity of both the sputtering and the annealing process. It is found that while the precursors are uniform both in morphology and composition, the annealing process introduces differences in grain size and metal content depending on the area considered on the 6-inch substrate. The corresponding solar cell is further divided into 184 small cells of 1 cm(2) to check the performance distribution across the device. Current-voltage characteristics and solar cell parameters are extracted. Natural convection inside the annealing chamber is suggested to affect significantly the heat distribution and a strong correlation between device performance and local temperature can be identified.

  • 5.
    Bras, Patrice
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Sterner, Jan
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Influence of hydrogen sulfide annealing on copper-zinc-tin-sulfide solar cells sputtered from a quaternary compound target2015In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 582, p. 233-238Article in journal (Refereed)
    Abstract [en]

    With a theoretical efficiency around 30% and an optimized band gap for sunlight absorption, Cu2ZnSnS4 (CZTS) is a promising, earth-abundant, material for thin film solar cells. Sputtering CZTS from a quaternary compound target is a quick and potentially industrial-scaled process that has not been investigated deeply yet. Our approach is based on an in-line vacuum system for the complete device. CZTS is sputtered from a compound target on a sodium molybdate (MoNa) pre-sputtered stainless steel substrate, and then annealed in high-pressure H2S atmosphere. A 1 mu m thick absorber is obtained within 7 minute sputtering. Top layers are then deposited, without vacuum breaking. The effects of different annealing temperatures on the absorber morphology and composition are investigated. It is observed that recrystallization already occurs at 420 degrees C and that crystallinity improves with increasing temperature up to 550 degrees C. However, micro-sphere formation underneath the film degrades the corresponding solar cell performance dramatically above 510 degrees C. It is shown that sodium is needed in order to enhance recrystallization of CZTS but the MoNa layer thickness seems not to be a critical parameter. Scanning electron microscopy, X-ray diffraction, X-ray fluorescence and current-voltage measurement were used to characterize the samples.

  • 6.
    Bras, Patrice
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Sterner, Jan
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Investigation of blister formation in sputtered Cu 2ZnSnS 4 absorbers for thin film solar cells2015In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 33, no 6, article id 061201Article in journal (Refereed)
    Abstract [en]

    Blister formation in Cu2ZnSnS4 (CZTS) thin films sputtered from a quaternary compound target is investigated. While the thin film structure, composition, and substrate material are not correlated to the blister formation, a strong link between sputtering gas entrapment, in this case argon, and blistering effect is found. It is shown that argon is trapped in the film during sputtering and migrates to locally form blisters during the high temperature annealing. Blister formation in CZTS absorbers is detrimental for thin film solar cell fabrication causing partial peeling of the absorber layer and potential shunt paths in the complete device. Reduced sputtering gas entrapment, and blister formation, is seen for higher sputtering pressure, higher substrate temperature, and change of sputtering gas to larger atoms. This is all in accordance with previous publications on blister formation caused by sputtering gas entrapment in other materials.

  • 7.
    Coronel, Ernesto
    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.
    Platzer Björkman, Charlotte
    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.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Microstructural characterization of Zn1-XMgXO buffers layer in CIGS solar cells2007Conference paper (Other academic)
  • 8.
    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.

  • 9.
    Ericson, Tove
    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.
    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.
    Reactive sputtering of precursors for Cu2ZnSnS4 thin film solar cells2012In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 520, no 24, p. 7093-7099Article in journal (Refereed)
    Abstract [en]

    The quaternary semiconductor Cu2ZnSnS4 (CZTS) is a possible In-free replacement for Cu(In,Ga)Se-2. Here we present reactive sputtering with the possibility to obtain homogeneous CZTS-precursors with tunable composition and a stoichiometric quantity of sulfur. The precursors can be rapidly annealed to create large grained films to be used in solar cells. The reactive sputtering process is flexible, and morphology, stress and metal and sulfur contents were varied by changing the H2S/Ar-flow ratio, pressure and substrate temperature. A process curve for the reactive sputtering from CuSn and Zn targets is presented. The Zn-target is shown to switch to compound mode earlier and faster compared to the CuSn-target. The precursors containing a stoichiometric amount of sulfur exhibit columnar grains, have a crystal structure best matching ZnS and give a broad peak, best matching CZTS, in Raman scattering. In comparing process gas flows it is shown that the sulfur content is strongly dependent on the H2S partial pressure but the total pressures compared in this study have little effect on the precursor properties. Increasing the substrate temperature changes the film composition due to the high vapor pressures of Zn, SnS and S. High substrate temperatures also give slightly denser and increasingly oriented films. The precursors are under compressive stress, which is reduced with higher deposition temperatures. (C) 2012 Elsevier B.V. All rights reserved.

  • 10.
    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.

  • 11.
    Ericson, Tove
    et al.
    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.
    Hultqvist, Adam
    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.
    Szaniawski, Piotr
    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.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zn(O,S) Buffer Layers and Thickness Variations of CdS Buffer for Cu2ZnSnS4 Solar Cells2014In: IEEE Journal of Photovoltaics, ISSN 2156-3381, Vol. 4, no 1, p. 465-469Article in journal (Refereed)
    Abstract [en]

    To improve the conduction band alignment and explore the influence of the buffer-absorber interface, we here investigate an alternative buffer for Cu2ZnSnS4 (CZTS) solar cells. The Zn(O, S) system was chosen since the optimum conduction band alignment with CZTS is predicted to be achievable, by varying oxygen to sulfur ratio. Several sulfur to oxygen ratios were evaluated to find an appropriate conduction band offset. There is a clear trend in open-circuit voltage Voc, with the highest values for the most sulfur rich buffer, before going to the blocking ZnS, whereas the fill factor peaks at a lower S content. The best alternative buffer cell in this series had an efficiency of 4.6% and the best CdS reference gave 7.3%. Extrapolating Voc values to 0 K gave activation energies well below the expected bandgap of 1.5 eV for CZTS, which indicate that recombination at the interface is dominating. However, it is clear that the values are affected by the change of buffer composition and that increasing sulfur content of the Zn(O, S) increases the activation energy for recombination. A series with varying CdS buffer thickness showed the expected behavior for short wavelengths in quantum efficiency measurements but the final variation in efficiency was small.

  • 12.
    Ericson, Tove
    et al.
    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.
    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.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Annealing behavior of reactively sputtered precursor films for Cu2ZnSnS4 solar cells2013In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 535, p. 22-26Article in journal (Refereed)
    Abstract [en]

    Reactively sputtered Cu–Zn–Sn–S precursor films are prepared and recrystallized by rapid thermal processing to generate Cu2ZnSnS4 solar cell absorber layers. We study how the film properties are affected by substrate heating and composition. The stress, density and texture in the films were measured. Compressive stress was observed for the precursors but did not correlate to the deposition temperature, and had no influence on the properties of the annealed films or solar cells. However, the substrate temperature during precursor deposition had a large effect on the behavior during annealing and on the solar cell performance. The films deposited at room temperature had, after annealing, smaller grains and cracks, and gave shunted devices. Cracking is suggested to be due to a slightly higher sulfur content, lower density or to minor differences in material quality. The grain size in the annealed films seems to increase with higher copper content and higher precursor deposition temperature. The best device in the current series gave an efficiency of 4.5%.

  • 13.
    Frisk, Christopher
    et al.
    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, Shu-Yi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Szaniawski, Piotr
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Olsson, Jörgen
    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.
    Combining strong interface recombination with bandgap narrowing and short diffusion length in Cu2ZnSnS4 device modeling2016In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 144, p. 364-370Article in journal (Refereed)
    Abstract [en]

    In this work we establish a device model in SCAPS, incorporating bandgap narrowing, short minority carrier diffusion length and interface recombination. The model is based on a reference device with standard structure; sputtered Mo on soda lime glass, a reactively sputtered and annealed Cu2ZnSnS4 (CZTS) absorber layer, chemical bath deposited CdS and sputtered i-ZnO buffer layers, and front contact formed with sputtered ZnO:Al and an evaporated Ni/Al/Ni grid. The efficiency of the reference device is 6.7%. Model parameter values of the absorber layer are based on the analysis of temperature dependent current–voltage (JVT) measurements, capacitance–voltage (CV) and drive-level capacitance profiling (DLCP) measurements, performed on the reference device, and on the comparison of simulated and measured quantum efficiency (QE) and current–voltage (JV) performance. Additional parameters are taken from literature. The key elements, electron–hole pair generation and recombination in the absorber layer, are the main focus in this study. Reported values of the absorption coefficient of CZTS vary around one order of magnitude when comparing data from reflectance–transmission (RT) measurements with ellipsometry measurements, and calculations. Therefore, a modified semi-empirical absorption coefficient, extracted from RT and QE measurements, with the depletion width from CV and DLCP, is presented and used in this study. The dominating recombination path is evaluated with JVT   analysis and the zero Kelvin activation energy (EA,0) is extracted from both temperature dependent open circuit voltage (VOC) and from modified Arrhenius plots. In each case,is found to be substantially smaller than the bandgap energy, even when considering bandgap narrowing due to disorder, which is an indication that the deficit observed in our CZTS device dominated by interface recombination. Finally, a complete device model is established, with JV   and QE simulations in good agreement with corresponding measurements, where the interface has the biggest impact on the Voc deficit, but with clear contribution from bulk recombination, with minority carrier diffusion length 250 nm, and from bandgap narrowing, giving a lower than nominal bandgap energy of 1.35 eV.

  • 14.
    Frisk, Christopher
    et al.
    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.
    Olsson, Jörgen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Szaniawski, Piotr
    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.
    Fjällström, Viktor
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Salome, P.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Optimizing Ga-profiles for highly efficient Cu(In,Ga)Se2 thin film solar cells in simple and complex defect models2014In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 47, no 48, p. 485104-Article in journal (Refereed)
    Abstract [en]

    Highly efficient Cu(In,Ga)(S,Se)2 photovoltaic thin film solar cells often have a compositional variation of Ga to In in the absorber layer, here described as a Ga-profile. In this work we have studied the role of Ga-profiles in four different models, based on input data from electrical and optical characterizations of an in-house state-of-the-art Cu(In,Ga)Se2 (CIGS) solar cell with power conversion efficiency above 19 %. A simple defect model with mid-gap defects in the absorber layer was compared with models with Ga-dependent defect concentrations and amphoteric defects. In these models optimized single-graded Ga-profiles have been compared with optimized double-graded Ga-profiles. It was found that the defect concentration for effective Shockley-Read-Hall recombination is low for high efficiency CIGS devices and that the doping concentration of the absorber layer, chosen according to the defect model, is paramount when optimizing Ga-profiles. For optimized single-graded Ga-profiles the simulated power conversion efficiency, depending on the model, is 20.5-20.8 %, and the equivalent double-graded Ga-profiles yield 20.6-21.4 %, indicating that the bandgap engineering of the CIGS device structure can lead to improvements in efficiency. Apart from the effects of increased doping in the complex defect models, the results are similar when comparing the complex defect models to the simple defect models. 

  • 15.
    Frisk, Christopher
    et al.
    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.
    Fjällström, Viktor
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Salomé, Pedro
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Olsson, Jörgen
    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.
    Modeling Ga-profiles for Cu(In,Ga)Se2 thin film solar cells with varying defect density2013In: 23rd International Photovoltaic Science and Engineering Conference; Taipei, Taiwan; October 28 - Nov 1, 2013: Proceedings, 2013Conference paper (Refereed)
    Abstract [en]

    The very best Cu(In,Ga)(S,Se)2 solar cells have a double graded band gap in the absorber, i.e. a notch profile, formed by varying the ratio of Ga to In. If this is a prerequisite or a consequence of high quality deposition methods is something yet of discussion. In this work we have constructed a high efficiency model (HE-T61) based on in-house state-of-the art Cu(In,Ga)Se2 solar cells, with efficiencies above 19 %, and investigated the role of the Ga-profile. Notch-type Ga-profiles have been compared with single graded profiles, and the influence of Ga-dependent defect distribution and metastable defects have been investigated showing that the optimum Ga-profile is dependent on such defect variations. It is also shown that within the HE-T61 model the optimized Ga-profile yields up to 3 % absolute efficiency gain, indicating that there is potential in band gap engineering.

  • 16.
    Frisk, Christopher
    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.
    Li, Shu-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.
    CZTS solar cell device simulation with varying absorber thickness2015In: 2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC). Proceedings, IEEE conference proceedings, 2015Conference paper (Refereed)
    Abstract [en]

    In this study the influence of absorber layer thickness on the trends of the four current-voltage (J-V) parameters for our CZTS solar cells is studied with simulations and compared with empirical data. In the case of dominating interface recombination we find that open-circuit voltage and fill-factor are largely unaffected of thickness variations 0.5 – 2.0 μm, whereas short-circuit current, and thereby efficiency, saturates (98 % of max) at >1.1 μm absorber thickness, in agreement with measurements. In the case of suppressed interface recombination all four J-V parameters exhibit strong thickness dependence at <0.5 μm due to back contact recombination.

  • 17.
    Frisk, Christopher
    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.
    Olsson, Jörgen
    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.
    Annoni, Filippo
    CNR, IMEM..
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    On the extraction of doping concentration from capacitance-voltage: A Cu2ZnSnS4 and ZnS sandwich structure2017In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 7, no 5, p. 1421-1425Article in journal (Refereed)
    Abstract [en]

    The capacitance-voltage (C-V) method is frequently used to evaluate the net doping of thin-film solar cells, an important parameter for the function of solar cells. However, complex materials such as kesterites are challenging to characterize. To minimize ambiguity when determining the apparent doping concentration (N-A) of Cu2ZnSnS4 (CZTS), we fabricated and investigated different structures: CZTS/ZnS metal-insulator-semiconductor (MIS) device, stand-alone CZTS and ZnS metal-sandwich structures, and CZTS solar cells. Characterization was carried out by means of admittance spectroscopy (AS) and C-V measurements. ZnS exhibits excellent intrinsic properties, and with the high-quality MIS sample we managed to successfully isolate the capacitive response of the CZTS itself. N-A, as extracted from the MIS structure, is found to be more reliable and four times higher compared with the solar cell, impacting any estimated collection efficiency substantially. Data herein presented also show that CZTS has a substantial low-frequency dispersive capacitance and the extraction of N-A depends on the chosen measurement frequency, symptoms of presence of deep defects. Furthermore, the CZTS/ZnS MIS structure is strongly resilient to leakage currents at both forward and reverse voltage bias where contribution from deep defects is minimized and maximized, respectively.

  • 18.
    Grini, Sigbjörn
    et al.
    Univ Oslo, Dept Phys, Ctr Mat Sci & Nanotechnol, POB 1048, N-0316 Oslo, Norway..
    Ross, Nils
    Univ Oslo, Dept Phys, Ctr Mat Sci & Nanotechnol, POB 1048, N-0316 Oslo, Norway..
    Sky, Thomas Neset
    Univ Oslo, Dept Phys, Ctr Mat Sci & Nanotechnol, POB 1048, N-0316 Oslo, Norway..
    Persson, Clas
    Univ Oslo, Dept Phys, Ctr Mat Sci & Nanotechnol, POB 1048, N-0316 Oslo, Norway..
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. Uppsala Univ, Solid State Elect, Angstrom Solar Ctr, Box 534, S-75121 Uppsala, Sweden..
    Vines, Lasse
    Univ Oslo, Dept Phys, Ctr Mat Sci & Nanotechnol, POB 1048, N-0316 Oslo, Norway..
    Secondary ion mass spectrometry as a tool to study selenium gradient in Cu2ZnSn(S,Se)42017In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, no 6, article id UNSP 1600187Article in journal (Refereed)
    Abstract [en]

    Secondary ion mass spectrometry (SIMS) has been utilized to study compositional gradients in compound-sputtered and annealed Cu2ZnSn(S,Se)(4) (CZTSSe). SIMS image depth profiling shows a non-uniform spatial distribution of selenium and supports a mechanism where selenization is accompanied by grain growth rather than substitution of selenium for sulfur. Furthermore, SIMS depth profiles of S and Se using O-2(+) primary ions and detecting molecular ions of the MCs+ type using Cs+ primary ions have been compared, where a linear relationship between the sulfur and selenium concentration suitable for compositional analysis is observed for concentrations with an Se/(S+Se) ratio in the range from 0.25 to 0.65. 3D image of the spatial Se distribution in a 20 x 20 mu m(2) grid measured with SIMS image depth profiling.

  • 19.
    Hultqvist, Adam
    et al.
    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.
    Törndahl, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ruth, Marta
    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.
    Optimization of i-ZnO window layers for Cu(In,Ga)Se2 solar cells with ALD buffers2007Conference paper (Refereed)
  • 20.
    Hultqvist, Adam
    et al.
    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.
    Coronel, Ernesto
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Experimental investigation of Cu(In1-x,Ga-x)Se-2/Zn(O1-z,S-z) solar cell performance2011In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 95, no 2, p. 497-503Article in journal (Refereed)
    Abstract [en]

    In this study we investigate the performance of Cu(In1-x,Ga-x)Se-2/Zn(O1-z,S-z) solar cells by changing the gallium content of the absorber layer in steps from CuInSe2 to CuGaSe2 and at each step vary the sulfur content of the Zn(O,S) buffer layer. By incorporating more or less sulfur into the Zn(O,S) buffer layer it is possible to change its morphology and band gap energy. Surprisingly, the best solar cells with Zn(O,S) buffer layers in this study are found for close to or the same Zn(O,S) buffer layer composition for all absorber Ga compositions. In comparison to their CdS references the best solar cells with Zn(O,S) buffer layers have slightly lower open circuit voltage, V-oc, lower fill factor, FF, and higher short circuit current density, J(sc), which result in comparable or slightly lower conversion efficiencies. The exception to this trend is the CuGaSe2 solar cells, where the best devices with Zn(O,S) have substantially lowered efficiency compared with the CdS reference, because of lower V-oc, FF and J(sc). X-ray photon spectroscopy and X-ray diffraction measurements show that the best Zn(O,S) buffer layers have similar properties independent of the Ga content. In addition, energy dispersive spectroscopy scans in a transmission electron microscope show evidence of lateral variations in the Zn(O,S) buffer layer composition at the absorber/buffer layer interface. Finally, a hypothesis based on the results of the buffer layer analysis is suggested in order to explain the solar cell parameters.

  • 21.
    Hultqvist, Adam
    et al.
    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.
    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.
    CuGaSe2 solar cells using atomic layer deposited Zn(O,S) and (Zn,Mg)O buffer layers2008Conference paper (Refereed)
  • 22.
    Hultqvist, Adam
    et al.
    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.
    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.
    CuGaSe2 solar cells using atomic layer deposited Zn(O,S) and (Zn,Mg)O buffer layers2009In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 517, no 7, p. 2305-2308Article in journal (Refereed)
    Abstract [en]

    The band gap of Zn(O,S) and (Zn,Mg)O buffer layers are varied with the objective of changing the conduction band alignment at the buffer layer/CuGaSe2 interface. To achieve this, alternative buffer layers are deposited using atomic layer deposition. The optimal compositions for CuGaSe2 solar cells are found to be close to the same for (Zn,Mg)O and the same for Zn(O,S) as in the CuIn0.7Ga0.3Se2 solar cell case. At the optimal compositions the solar cell conversion efficiency for (Zn,Mg)O buffer layers is 6.2% and for Zn(O,S) buffer layers it is 3.9% compared to the CdS reference cells which have 5-8% efficiency.

  • 23.
    Hultqvist, Adam
    et al.
    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.
    Zimmermann, Uwe
    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.
    Törndahl, Tobias
    Fasta tillståndets elektronik. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electronics.
    Growth kinetics, properties, performance and stability of ALD Zn-Sn-O buffer layers for Cu(In,Ga)Se2 solar cellsManuscript (preprint) (Other academic)
    Abstract [en]

    A new ALD process is developed for deposition of Zn-Sn-O buffer layers for Cu(In,Ga)Se2 solar cells with tetrakis(dimethylamino) tin, Sn(N(CH3)2)4, diethyl zinc, Zn(C5H5)2 and water, H2O. The new process gives excellent control of thickness and [Sn]/([Sn]+[Zn]) ratio of the films. The Zn-Sn-O films are amorphous as found by grazing incidence x-ray diffraction, have a high resistivity, show a low density compared to ZnO and SnOx and have a transmittance loss that is smeared out over a wide wavelength interval. Good solar cell performance is achieved for [Sn]/([Sn]+[Zn]) ratios determined to be 0.15 – 0.21 by Rutherford backscattering. The champion solar cell with a Zn-Sn-O buffer layer has an efficiency of 15.3 % (Voc = 653 mV, Jsc(QE) = 31.8 mA/cm2 and FF = 73.8 %)  compared to 15.1 % (Voc = 663 mV, Jsc(QE) = 30.1 mA/cm2 and FF = 75.8 %) of the best reference solar cell with a CdS buffer layer. There is a strong lightsoaking effect that saturates after a few minutes for solar cells with Zn-Sn-O buffer layers after storage in the dark. Stability was tested by 1000 h of dry heat storage in darkness at 85 °C, where Zn-Sn-O buffer layers with a thickness of 76 nm, did retain their initial value after a few minutes of light soaking.

  • 24.
    Hultqvist, Adam
    et al.
    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.
    Zimmermann, Uwe
    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.
    Törndahl, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Growth kinetics, properties, performance, and stability of atomic layer deposition Zn–Sn–O buffer layers for Cu(In,Ga)Se2 solar cells2012In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 20, no 7, p. 883-891Article in journal (Refereed)
    Abstract [en]

    A new atomic layer deposition process was developed for deposition of Zn–Sn–O buffer layers for Cu(In,Ga)Se2 solar cells with tetrakis(dimethylamino) tin, Sn(N(CH3)2)4, diethyl zinc, Zn(C2H5)2, and water, H2O. The new processgives good control of thickness and [Sn]/([Sn]+[Zn]) content of the films. The Zn–Sn–O films are amorphous as foundby grazing incidence X-ray diffraction, have a high resistivity, show a lower density compared with ZnO and SnOx, andhave a transmittance loss that is smeared out over a wide wavelength interval. Good solar cell performance was achievedfor a [Sn]/([Sn]+[Zn]) content determined to be 0.15–0.21 by Rutherford backscattering. The champion solar cell with aZn–Sn–O buffer layer had an efficiency of 15.3% (Voc=653mV, Jsc(QE)=31.8mA/cm2, and FF=73.8%) compared with15.1% (Voc=663mV, Jsc(QE)=30.1mA/cm2, and FF=75.8%) of the best reference solar cell with a CdS buffer layer. Thereis a strong light-soaking effect that saturates after a few minutes for solar cells with Zn–Sn–O buffer layers after storage in thedark. Stability was tested by 1000h of dry heat storage in darkness at 85°C, where Zn–Sn–O buffer layers with a thicknessof 76nm retained their initial value after a few minutes of light soaking.

  • 25. Igalson, M
    et al.
    Platzer Björkman, Charlotte
    Fasta tillståndets elektronik. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electronics.
    The influence of buffer layer on the transient behaviour of thin film chalcopyrite devices2004In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, Vol. 84, no 1-4, p. 93-103Article in journal (Refereed)
  • 26.
    Jacobsson, Jesper T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Platzer-Björkman, Charlotte
    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.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    CuInxGa1-xSe2 as an efficient photocathode for solar hydrogen generation2013In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 38, no 35, p. 15027-15035Article in journal (Refereed)
    Abstract [en]

    Utilizing the energy in the sun to efficiently split water into hydrogen and oxygen can have a huge beneficial impact on a future post-carbon energy system. There is still, however, some way to go before this concept will be fully competitive. At the heart of the problem is finding and designing materials that can drive the photoreaction in an efficient and stable way. In this work we demonstrate how CIGS (CuInxGa1-xSe2), can be used for photo reduction of water into hydrogen. CIGS, which is a proven good solar cell material, does not in itself have the appropriate energetics to drive the reaction to any larger extent. Here we show that by utilizing a solid state pn-junction for charge separation and a catalyst deposited on the surface, the efficiency is significantly improved and photocurrents of 6 mA/cm(2) are demonstrated for the reduction reaction in the configuration of a photo-electrochemical cell. The stability of CIGS in water under illumination turns out to be a problem. In our present set-up, we demonstrate that separation between the charge carrier generation, which takes place in the solar cell, from the catalysis, which takes place in the electrolyte leads to improved stability, while keeping the essential functions of the processes. By incorporating appropriate charge separation layers and optimizing the catalytic conditions at the surface of the electrodes, photocurrents in excess of 20 mA/cm2 are reached for the reduction half reaction, demonstrating how essentially the full potential of GIGS as an efficient absorber material can be utilized in photocatalytic reduction of water into hydrogen.

  • 27.
    Johansson, E
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Platzer-Björkman, C
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Rensmo, H
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Sandell, A
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Siegbahn, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Stolt, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Gorgoi, M
    Svensson, S
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Lewin, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry. oorganisk kemi.
    Schäfers, F
    Braun, W
    Eberhardt, W
    HIKE experiments at KMC-1: Studies of Solar Cell Materials2007In: Berliner Elektronenspeicherring-Gesellschaft für Synchrotronstrahlung m.b.H. (BESSY) Annual Report (2006), no 508-509Article in journal (Refereed)
  • 28.
    Kosyak, Volodymyr
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Postnikov, A. V.
    Univ Lorraine, ICPM, Inst Jean Barriol, LCP A2MC, 1 Bd Arago, F-57078 Metz, France..
    Scragg, Jonathan J.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scarpulla, M. A.
    Univ Utah, Mat Sci & Engn, Salt Lake City, UT 84112 USA.;Univ Utah, Elect & Comp Engn, Salt Lake City, UT 84112 USA..
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Calculation of point defect concentration in Cu2ZnSnS4: Insights into the high-temperature equilibrium and quenching2017In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 122, no 3, article id 035707Article in journal (Refereed)
    Abstract [en]

    Herein, we study the native point defect equilibrium in Cu2ZnSnS4 (CZTS) by applying a statistical thermodynamic model. The stable chemical- potential space (SCPS) of CZTS at an elevated temperature was estimated directly, on the basis of deviations from stoichiometry calculated for the different combinations of chemical potential of the components. We show that the SCPS is narrow due to high concentration of (V-Cu(-) Zn-Cu(+)) complex which is dominant over other complexes and isolated defects. The CZTS was found to have p-type conductivity for both stoichiometric and Cu-poor/Zn-rich composition. It is established that the reason for this is that the majority of donor-like Zn-Cu(+) antisites are involved in the formation of (V-Cu(-) Zn-Cu(+)) complex making Cu-Zn dominant and providing p- type conductivity even for Cu-poor/Zn-rich composition. However, our calculation reveals that the hole concentration is almost insensitive to the variation of the chemical composition within the composition region of the single-phase CZTS due to nearly constant concentration of dominant charged defects. The calculations for the full equilibrium and quenching indicate that hole concentration is strongly dependent on the annealing temperature and decreases substantially after the drastic cooling. This means that the precise control of annealing temperature and post-annealing cooling rate are critical for tuning the electrical properties of CZTS.

  • 29.
    Kubart, Tomas
    et al.
    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.
    Scragg, Jonathan J.
    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-Bjorkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Reactive sputtering of Cu2ZnSnS4 thin films - Target effects on the deposition process stability2014In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 240, p. 281-285Article in journal (Refereed)
    Abstract [en]

    Cu2ZnSnS4 (TS) is a promising material for thin film solar cells which contains only abundant elements. This work focuses on the stability of elemental composition of films deposited by reactive sputtering of CuSn alloy targets in H2S. Long equilibration times of several hours were observed. The main reason is the formation of a thick Cu2S layer on the target surface. Especially in areas with low erosion rate, the Cu2S thickness reaches up to 700 pm and is accompanied by a preferential loss of Sn from the target. Based on the results, it is suggested that the formation of Cu2S may be limited either by more uniform erosion of the target surface or by reduction of the H2S partial pressure.

  • 30.
    Kubart, Tomas
    et al.
    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.
    Scragg, Jonathan
    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.
    Reactive magnetron sputtering of precursors for CZTS solar cells2012Conference paper (Refereed)
    Abstract [en]

    At the moment, CIGS (CuInGaSe2) solar cells show the highest efficiency among industrial scale produced thin film solar cells. Given the present strong increase in production, however, the availability and price of indium will become an issue because of its low abundance in Earth's crust. Therefore, there is strong interest in alternative indium free absorber materials. Kesterites CZTS (Cu2ZnSn(SxSe1-x)4) attracted most attention owing to the fact that relatively high efficiencies have already been demonstrated and also due to the similarity to CIGS. In this contribution we report on reactive sputtering for deposition of CZTS precursors. In order to avoid Sn loss at elevated temperatures a two stage process, synthesis of precursor films at relatively low substrate temperature followed by annealing, is used. Depositions are performed by pulsed DC magnetron sputtering from two targets, a CuSn alloy and Zn, in a mixture of Ar and H2S. The film structure is evaluated by X-ray diffraction and Raman spectroscopy while the composition is analysed by RBS, XRF, EDS and EPMA. Internal stress is measured by deflection of thin substrates. Characteristics of the deposition process are discussed with respect to the discharge power, total pressure, substrate temperature and H2S flow on the film structure and composition.

    Sulphur incorporation can be readily controlled by H2S flow with the structure changing from amorphous to columnar with increasing S content. The main issue encountered in the depositions is related to the film composition as the ratio between Cu and Sn does not correspond to the target composition. This effect is discussed in detail with respect to the sputtering and transport through the gas phase. Finally, material properties after annealing are briefly summarized.

  • 31.
    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.

  • 32.
    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.

  • 33.
    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.

  • 34.
    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.

  • 35.
    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.

  • 36.
    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.

  • 37.
    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).

  • 38.
    Lindahl, Johan
    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.
    Szaniawski, Piotr
    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.
    Hultqvist, Adam
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Salomé, Pedro
    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.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Inline Cu(In,Ga)Se-2 Co-evaporation for High-Efficiency Solar Cells and Modules2013In: IEEE JOURNAL OF PHOTOVOLTAICS, ISSN 2156-3381, Vol. 3, no 3, p. 1100-1105Article in journal (Refereed)
    Abstract [en]

    In this paper, co-evaporation of Cu(In,Ga)Se-2 (CIGS) in an inline single-stage process is used to fabricate solar cell devices with up to 18.6% conversion efficiency using a CdS buffer layer and 18.2% using a Zn1-xSnxOy Cd-free buffer layer. Furthermore, a 15.6-cm(2) mini-module, with 16.8% conversion efficiency, has been made with the same layer structure as the CdS baseline cells, showing that the uniformity is excellent. The cell results have been externally verified. The CIGS process is described in detail, and material characterization methods show that the CIGS layer exhibits a linear grading in the [Ga]/([Ga]+[In]) ratio, with an average [Ga]/([Ga]+[In]) value of 0.45. Standard processes for CdS as well as Cd-free alternative buffer layers are evaluated, and descriptions of the baseline process for the preparation of all other steps in the Angstrom Solar Center standard solar cell are given.

  • 39.
    Malm, Ulf
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Malmström, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Materials Science.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Stolt, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Determination of dominant recombination paths in Cu(In,Ga)Se2 thin-film solar cells with ALD-ZnO buffer layers2005In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 480-481, p. 208-212Article in journal (Refereed)
    Abstract [en]

    CuIn1−xGaxSe2 (CIGS) and CuInSe2 (CIS) thin-film solar cells, with ZnO buffer layers deposited by Atomic Layer Deposition (ALD), are examined with respect to dominant recombination path. They are compared with reference cells with CdS buffer layers. The principal method of examination is temperature-dependent JV characterization (J(V)T), and the analysis of the J(V)T data has been modified in order to more reliably discern the dominant recombination path.

    Compared to the CIS cells with the traditional CdS buffer layer, the CIS cells with ALD–ZnO buffer layer exhibit the same dominant recombination path, i.e., recombination in the bulk of the absorber. For the CIGS cells (with [Ga]/([Ga]+[In])=0.3), however, the analysis of the cells with ALD–ZnO buffer points to dominant interface recombination, while the CdS buffer cells are dominated by bulk recombination.

    For CIGS, the difference between the recombination in ALD–ZnO and CdS cells is consistent with the negative conduction band offset found by photoelectron spectroscopy in these ALD–ZnO cells in a previous study. This offset leads to increased interface recombination.

    For CIS/ALD–ZnO, it was previously found that there is no negative conduction band offset since the conduction band minimum of the absorber is lower. Consistently there is no difference in dominant recombination path between ALD–ZnO buffer cells and traditional CdS buffer cells.

  • 40.
    Marko, Hakim
    et al.
    Institut des Matériaux Jean Rouxel, Nantes University, CNRS and CEA, LITEN, Grenoble.
    Hultqvist, Adam
    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.
    Noël, Sébastien
    CEA, LITEN, Grenoble.
    Kessler, John
    Institut des Matériaux Jean Rouxel, Nantes University, CNRS.
    Effects of CuIn0,5Ga0,5Se2 growth by isothermal and bithermal Cu-Poor/Rich/Poor sequence on solar cells properties2009In: Thin-Film Compound Semiconductor Photovoltaics — 2009 / [ed] A. Yamada, C. Heske, M. Contreras, M. Igalson, S.J.C. Irvine, Warrendale, PA: Material Research Society , 2009, , p. 6Conference paper (Other academic)
    Abstract [en]

    Co-evaporated CuIn0,5Ga0,5Se2 thin film solar cells were grown using a sequential Cu-Poor/Rich/Poor process (CUPRO). During the growth process, the substrate temperature was either kept constant at 570 °C (iso-CUPRO) or decreased during the first step to either 360 or 430 or 500 °C (bi-CUPRO). According to atomic force microscopy (AFM) measurements, the lower the temperature is in the first step the smoother the final CIGS surface becomes. By decreasing the first step temperature, cross-section scanning electron microscopy (SEM) and q-2q x-ray diffraction (XRD) do not reveal clearly any important changes of morphology and crystallographic preferred orientation. SLG/Mo/CIGS/Buffer layer/i-ZnO/ZnO:Al/grid(Ni/Al/Ni)solar cells with either a chemical bath deposited CdS or an atomic layer deposited Zn(O,S) buffer layer were fabricated. For both buffer layers, the bi-CUPRO processes lead to higher efficiencies. Besides, using Zn(O,S), the electronic collection was improved for the infrared spectrum as well as for the ultraviolet spectrum. This resulted in efficiencies close to 14,5 % for the Zn(O,S) cells.

  • 41.
    Mongstad, T
    et al.
    Institute for Energy Technology, Kjeller, Norge.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Karazhanov, S Zh
    Institute for Energy Technology, Kjeller, Norge.
    Holt, A
    Institute for Energy technology, Kjeller, Norge.
    Maehlen, J P
    Institute for Energy Technology, Kjeller, Norge.
    Hauback, B C
    Institute for Energy Technology, Kjeller, Norge.
    Transparent yttrium hydride thin films prepared by reactive sputtering2011In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 509, p. S812-S816Article in journal (Refereed)
    Abstract [en]

    Metal hydrides have earlier been suggested for utilization in solar cells. With this as a motivation we have prepared thin films of yttrium hydride by reactive magnetron sputter deposition. The resulting films are metallic for low partial pressure of hydrogen during the deposition, and black or yellow-transparent for higher partial pressure of hydrogen. Both metallic and semiconducting transparent YH(x) films have been prepared directly in situ without the need of capping layers and post-deposition hydrogenation. Optically the films are similar to what is found for YH(x) films prepared by other techniques, but the crystal structure of the transparent films differ from the well-known YH(3-eta) phase, as they have an fcc lattice instead of hcp.

  • 42. Mongstad, T.
    et al.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Karazhanow, S. Zh.
    Holt, A.
    Maehlen, J. P.
    Hauback, B.
    Transparent yttrium hydride thin films prepared by reactive sputtering2010Conference paper (Refereed)
  • 43.
    Mongstad, Trygve
    et al.
    Institute for Energy Technology, Norway.
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Maehlen, Jan-Petter
    Institute for Energy Technology, Norway.
    Mooij, Lennard
    Delft University of Technology.
    Pivak, Yevheniy
    Delft University of Technology.
    Dam, Bernard
    Delft University of Technology.
    Marstein, Erik
    Institute for Energy Technology, Norway.
    Hauback, Björn
    Institute for Energy Technology, Norway.
    Karazhanov, Smagul
    Institute for Energy Technology, Norway.
    A new thin film photochromic material: oxygen-containing yttrium hydride2011In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 95, no 12, p. 3596-3599Article in journal (Refereed)
    Abstract [en]

    In this work we report on photochromism in transparent thin film samples of oxygen-containing yttrium hydride. Exposure to visible and ultraviolet (UV) light at moderate intensity triggers a decrease in the optical transmission of visible and infrared (IR) light. The photo-darkening is colour-neutral. We show that the optical transmission of samples of 500 nm thickness can be reduced by up to 50% after one hour of illumination with light of moderate intensity. The reaction is reversible and samples that are left in the dark return to the initial transparent state. The relaxation time in the dark depends on the temperature of the sample and the duration of the light exposure. The photochromic reaction takes place under ambient conditions in the as-deposited state of the thin-film samples.

  • 44.
    Mongstad, Trygve
    et al.
    Institute for Energy Technology, Kjeller, Norge.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Maehlen, J. P.
    Institute for Energy Technology, Kjeller, Norge.
    Hauback, B. C.
    Institute for Energy Technology, Kjeller, Norge.
    Karazhanov, S. Zh.
    Institute for Energy Technology, Kjeller, Norge.
    Cousin, F.
    Laboratoire Léon Brillouin, CEA Saclay, Gif-sur-Yvette, Frankrike.
    Surface oxide on thin films of yttrium hydride studied by neutron reflectometry2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, no 19, p. 191604-Article in journal (Refereed)
    Abstract [en]

    The applicability of standard methods for compositional analysis is limited for H-containing films. Neutron reflectometry is a powerful, non-destructive method that is especially suitable for these systems due to the large negative scattering length of H. In this work, we demonstrate how neutron reflectometry can be used to investigate thin films of yttrium hydride. Neutron reflectometry gives a strong contrast between the film and the surface oxide layer, enabling us to estimate the oxide thickness and oxygen penetration depths. A surface oxide layer of 5-10nm thickness was found for unprotected yttrium hydride films.

  • 45.
    Mongstad, Trygve
    et al.
    Institute for Energy Technology, Kjeller, Norge.
    You, C. C.
    Institute for Energy Technology, Kjeller, Norge.
    Thogersen, A.
    Institute for Energy Technology, Kjeller, Norge.
    Maehlen, J. P.
    Institute for Energy Technology, Kjeller, Norge.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Hauback, B. C.
    Institute for Energy Technology, Kjeller, Norge.
    Karazhanov, S. Zh
    Institute for Energy Technology, Kjeller, Norge.
    MgyNi1-y(H-x) thin films deposited by magnetron co-sputtering2012In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 527, p. 76-83Article in journal (Refereed)
    Abstract [en]

    In this work we have synthesized thin films of MgyNi1-y(H-x) metal and metal hydride with y between 0 and 1. The films are deposited by magnetron co-sputtering of metallic targets of Mg and Ni. Metallic MgyNi1-y films were deposited with pure Ar plasma while MgyNi1-yHx hydride films were deposited reactively with 30% H-2 in the Ar plasma. The depositions were done with a fixed substrate carrier, producing films with a spatial gradient in the Mg and Ni composition. The combinatorial method of co-sputtering gives an insight into the phase diagram of MgyNi1-y and MgyNi1-yHx, and allows us to investigate structural, optical and electrical properties of the resulting alloys. Our results show that reactive sputtering gives direct deposition of metal hydride films, with high purity in the case of Mg similar to 2NiH similar to 4. We have observed limited oxidation after several months of exposure to ambient conditions. MgyNi1-y and MgyNi1-yHx films might be applied for optical control in smart windows, optical sensors and as a semiconducting material for photovoltaic solar cells.

  • 46. Naghavi, N.
    et al.
    Abou-Ras, D.
    Allsop, N.
    Barreau, N.
    Buecheler, S.
    Ennaoui, A.
    Fischer, C. -H
    Guillen, C.
    Hariskos, D.
    Herrero, J.
    Klenk, R.
    Kushiya, K.
    Lincot, D.
    Menner, R.
    Nakada, T.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Spiering, S.
    Tiwari, A. N.
    Törndahl, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Buffer layers and transparent conducting oxides for chalcopyrite Cu(In,Ga)(S,Se)(2) based thin film photovoltaics: Present status and current developments2010In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 18, no 6, p. 411-433Article in journal (Refereed)
    Abstract [en]

    The aim of the present contribution is to give a review on the recent work concerning Cd-free buffer and window layers in chalcopyrite solar cells using various deposition techniques as well as on their adaptation to chalcopyrite-type absorbers such as Cu(In,Ga)Se-2, CuInS2, or Cu(In,Ga)(S,Se)(2). The corresponding solar-cell performances, the expected technological problems, and current attempts for their commercialization will be discussed. The most important deposition techniques developed in this paper are chemical bath deposition, atomic layer deposition, ILGAR deposition, evaporation, and spray deposition. These deposition methods were employed essentially for buffers based on the following three materials: In2S3, ZnS, Zn1-xMgxO.

  • 47. Persson, Clas
    et al.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Malmström, 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, Electronics.
    Strong valence-band offset bowing of ZnO1-xSx enhances p-type nitrogen doping of ZnO-like alloys2006In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, no 14, p. 146403-Article in journal (Refereed)
    Abstract [en]

    Photoelectron spectroscopy, optical characterization, and density functional calculations of ZnO1-xSx reveal that the valence-band (VB) offset E-v(x) increases strongly for small S content, whereas the conduction-band edge E-c(x) increases only weakly. This is explained as the formation of local ZnS-like bonds in the ZnO host, which mainly affects the VB edge and thereby narrows the energy gap: E-g(x=0.28)approximate to E-g(ZnO)-0.6 eV. The low-energy absorption tail is a direct Gamma(v)->Gamma(c) transition from ZnS-like VB. The VB bowing can be utilized to enhance p-type N-O doping with lower formation energy Delta H-f and shallower acceptor state in the ZnO-like alloys.

  • 48.
    Pettersson, Jonas
    et al.
    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.
    Electrical modeling of Cu(In,Ga)Se2 cells with ALD-Zn1xMgxO bufferlayers2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 1, p. 014509-014509Article in journal (Refereed)
    Abstract [en]

    Electrical modeling of Cu(In,Ga)Se2 solar cells with Zn1-xMgxO buffer layers is performed. A number of  different  device  models  are  implemented  and  tested  by  comparing  simulation  results  and measurement data. Room temperature light-soaking and dark-light cross-over behavior as well aslow-temperature characteristics of these cells are studied. The light-soaking improvements in the solarcell  parameters  are  attributed  to  an  increase  in  buffer  donor  density,  due  to  persistent  photoconductivity, that counteracts charged acceptors in the absorber-buffer region. Dark-light JV-curvecross-over is explained by deep acceptor defects with small electron capture cross-section, in thebuffer. Best correspondence to measurements on ZnO and Zn0.83Mg0.17O cells is obtained with models including absorber-buffer interface acceptor states. No wideband-gap surface defect layer is needed to reproduce measurement data.

  • 49.
    Pettersson, Jonas
    et al.
    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.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Temperature-dependent current-voltage and lightsoaking measurements on Cu(In,Ga)Se2 solar cells with ALD-Zn1-xMgxO buffer layers2009In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 17, no 7, p. 460-469Article in journal (Refereed)
    Abstract [en]

    In this paper, lightsoaking and temperature-dependent current-voltage (JVT) measurements on Cu(In,Ga)Se2 solar cells with atomic layer deposited Zn1-xMgxO buffer layers are presented. A range of Mg concentrations are used, from pure ZnO (x=0) to 26% Mg (x=0·26). Since this kind of solar cells exhibit strong metastable behaviour, lightsoaking is needed prior to the JVT-measurements to enable fitting of these to the one-diode model. The most prominent effect of lightsoaking cells with Mg-rich buffer layers is an increased fill factor, while the effect on cells with pure ZnO buffer is mainly to increase Voc·. The activation energy is extracted from JVT-measurement data by applying three different methods and the ideality factors are fitted to two different models of temperature-dependence. A buffer layer consisting either of ZnO or Zn1-xMgxO with a minor Mg content gives solar cells dominated by interface recombination, which probably can be related to a negative conduction band offset. A relatively high Mg content in the buffer layer (x=0·21) leads to solar cells dominated by recombination in the space charge region. The recombination is interpreted as being tunnelling-enhanced. The situation in between these Mg concentrations is less clear. Before lightsoaking, the sample with x=0·12 has the highest efficiency of 15·3%, while after lightsoaking the sample with x=0·21 holds the best efficiency, 16·1%, exceeding the value for the CdS reference. The Jsc values of the Zn1-xMgxO cells surpass that of the reference due to the larger bandgap of Zn1-xMgxO compared to CdS.

  • 50.
    Pettersson, Jonas
    et al.
    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.
    Hultqvist, Adam
    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.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Measurements of photo-induced changes in the conduction properties of ALD-Zn1−xMgxO thin films2010In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T141, p. 014010-1-014010-4Article in journal (Refereed)
    Abstract [en]

    Resistivity and Hall measurements are conducted on atomic layer deposited Zn1−xMgxO thin films of different thicknesses and compositions. It is found that the films exhibit persistent photoconductivity after UV-light exposure. The effect is more pronounced for thinner films with higher magnesium content. These are also the films with the highest resistivity. Light-induced excess conductivity is still present in some of the films after weeks of dark storage. Conductivity relaxation is faster at higher temperatures. From Hall measurements, it is observed that conductivity changes are a combined effect of changes in the mobility and concentration of free carriers.

123 1 - 50 of 103
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