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  • 1.
    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, 367-374 p.Article 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.

  • 2.
    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 2367-198XArticle 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.

    The full text will be freely available from 2018-04-07 00:00
  • 3.
    Frisk, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Modeling and electrical characterization of Cu(In,Ga)Se2 and Cu2ZnSnS4 solar cells2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, modeling and electrical characterization have been performed on Cu(In,Ga)Se2 (CIGS) and Cu2ZnSnS4 (CZTS) thin film solar cells, with the aim to investigate potential improvements to power conversion efficiency for respective technology. The modeling was primarily done in SCAPS, and current-voltage (J-V), quantum efficiency (QE) and capacitance-voltage (C-V) were the primary characterization methods. In CIGS, models of a 19.2 % efficient reference device were created by fitting simulations of J-V and QE to corresponding experimental data. Within the models, single and double GGI = Ga/(Ga+In) gradients through the absorber layer were optimized yielding up to 2 % absolute increase in efficiency, compared to the reference models. For CIGS solar cells of this performance level, electron diffusion length (Ln) is comparable to absorber thickness. Thus, increasing GGI towards the back contact acts as passivation and constitutes largest part of the efficiency increase. For further efficiency increase, majority bottlenecks to improve are optical losses and electron lifetime in the CIGS. In a CZTS model of a 6.7 % reference device, bandgap (Eg) fluctuations and interface recombination were shown to be the majority limit to open circuit voltage (Voc), and Shockley-Read-Hall (SRH) recombination limiting Ln and thus being the majority limit to short-circuit current and fill-factor. Combined, Eg fluctuations and interface recombination cause about 10 % absolute loss in efficiency, and SRH recombination about 9 % loss, compared to an ideal system. Part of the Voc-deficit originates from a cliff-type conduction band offset (CBO) between CZTS and the standard CdS buffer layer, and the energy of the dominant recombination path (EA) is around 1 eV, well below Eg for CZTS. However, it was shown that the CBO could be adjusted and improved with Zn1-xSn­xOy buffer layers. Best results gave EA = 1.36 eV, close to Eg = 1.3-1.35 eV for CZTS as given by photoluminescence, and the Voc-deficit decreased almost 100 mV. Experimentally by varying the absorber layer thickness in CZTS devices, the efficiency saturated at <1 μm, due to short Ln, expected to be 250-500 nm, and narrow depletion width, commonly of the order 100 nm in in-house CZTS. Doping concentration (NA) determines depletion width, but is critical to device performance in general. To better estimate NA with C-V, ZnS and CZTS sandwich structures were created, and in conjunction with simulations it was seen that the capacitance extracted from CZTS is heavily frequency dependent. Moreover, it was shown that C-V characterization of full solar cells may underestimate NA greatly, meaning that the simple sandwich structure might be preferable in this type of analysis. Finally, a model of the Cu2ZnSn(S,Se)4 was created to study the effect of S/(S+Se) gradients, in a similar manner to the GGI gradients in CIGS. With lower Eg and higher mobility for pure selenides, compared to pure sulfides, it was seen that increasing S/(S+Se) towards the back contact improves efficiency with about 1 % absolute, compared to the best ungraded model where S/(S+Se) = 0.25. Minimizing Eg fluctuation in CZTS in conjunction with suitable buffer layers, and improving Ln in all sulfo-selenides, are needed to bring these technologies into the commercial realm.

    List of papers
    1. Optimizing Ga-profiles for highly efficient Cu(In,Ga)Se2 thin film solar cells in simple and complex defect models
    Open this publication in new window or tab >>Optimizing Ga-profiles for highly efficient Cu(In,Ga)Se2 thin film solar cells in simple and complex defect models
    Show others...
    2014 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 47, no 48, 485104- p.Article in journal (Refereed) Published
    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. 

    Keyword
    Solar cell, CIGS, modelling, simulation, optimizing, Ga-profile
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Electronics
    Identifiers
    urn:nbn:se:uu:diva-235838 (URN)10.1088/0022-3727/47/48/485104 (DOI)000344941100009 ()
    Funder
    Swedish Research Council, B0393101Swedish Energy Agency
    Available from: 2014-11-17 Created: 2014-11-11 Last updated: 2017-12-05Bibliographically approved
    2. Combining strong interface recombination with bandgap narrowing and short diffusion length in Cu2ZnSnS4 device modeling
    Open this publication in new window or tab >>Combining strong interface recombination with bandgap narrowing and short diffusion length in Cu2ZnSnS4 device modeling
    Show others...
    2016 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 144, 364-370 p.Article in journal (Refereed) Published
    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.

    Keyword
    absorption coefficient, CZTS, interface recombination, kesterite, modeling, simulation.
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:uu:diva-268929 (URN)10.1016/j.solmat.2015.09.019 (DOI)000366223900047 ()
    Funder
    Swedish Energy Agency, 32787-3Swedish Research Council, B0393101
    Available from: 2015-12-11 Created: 2015-12-11 Last updated: 2017-12-01Bibliographically approved
    3. Reduced interface recombination in Cu2ZnSnS4 solar cells with atomic layer deposition Zn1-xSnxO buffer layers
    Open this publication in new window or tab >>Reduced interface recombination in Cu2ZnSnS4 solar cells with atomic layer deposition Zn1-xSnxO buffer layers
    Show others...
    2015 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, no 24, 243904Article in journal (Refereed) Published
    Abstract [en]

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

    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:uu:diva-268548 (URN)10.1063/1.4937998 (DOI)000367318600062 ()
    Funder
    Swedish Energy AgencySwedish Research CouncilSwedish Foundation for Strategic Research
    Available from: 2015-12-07 Created: 2015-12-07 Last updated: 2017-12-01Bibliographically approved
    4. CZTS solar cell device simulation with varying absorber thickness
    Open this publication in new window or tab >>CZTS solar cell device simulation with varying absorber thickness
    2015 (English)In: 2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC). Proceedings, IEEE conference proceedings, 2015Conference paper, Published 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.

    Place, publisher, year, edition, pages
    IEEE conference proceedings, 2015
    Series
    IEEE Photovoltaic Specialists Conference, ISSN 0160-8371
    Keyword
    absorber layer, CZTS, device model, photovoltaic cells, simulations
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:uu:diva-268931 (URN)10.1109/PVSC.2015.7355794 (DOI)000369992900204 ()978-1-4799-7944-8 (ISBN)
    Conference
    IEEE 42nd Photovoltaic Specialists Conference, 14-19 June 2015, New Orleans, LA, USA
    Available from: 2015-12-11 Created: 2015-12-11 Last updated: 2017-04-18Bibliographically approved
    5. Influence of the Cu2ZnSnS4 absorber thickness on thin film solar cells
    Open this publication in new window or tab >>Influence of the Cu2ZnSnS4 absorber thickness on thin film solar cells
    2015 (English)In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396XArticle in journal (Refereed) Published
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-265420 (URN)DOI: 10.1002/pssa.201532311 (DOI)
    Available from: 2015-10-28 Created: 2015-10-28 Last updated: 2017-12-01
    6. Potential of CuS cap to prevent decomposition of Cu2ZnSnS4 during annealing
    Open this publication in new window or tab >>Potential of CuS cap to prevent decomposition of Cu2ZnSnS4 during annealing
    Show others...
    2015 (English)In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 212, no 12, 2843-2849 p.Article in journal (Refereed) Published
    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.

    Keyword
    cap layer;Cu2ZnSnS4;kesterite;solar cells;thin films
    National Category
    Condensed Matter Physics Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-263983 (URN)10.1002/pssa.201532420 (DOI)000366589900028 ()
    Funder
    Swedish Research CouncilSwedish Foundation for Strategic Research EU, FP7, Seventh Framework Programme, 316488
    Available from: 2015-10-05 Created: 2015-10-05 Last updated: 2017-12-01Bibliographically approved
    7. On the extraction of doping concentration from capacitance-voltage: A Cu2ZnSnS4 and ZnS sandwich structure
    Open this publication in new window or tab >>On the extraction of doping concentration from capacitance-voltage: A Cu2ZnSnS4 and ZnS sandwich structure
    Show others...
    2017 (English)In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 7, no 5, 1421-1425 p.Article in journal (Refereed) Published
    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.

    Keyword
    Admittance measurement, capacitance-voltage characteristics, kesterite, modeling, semiconductor device doping
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-320307 (URN)10.1109/JPHOTOV.2017.2711427 (DOI)000408160700034 ()
    Funder
    Swedish Research CouncilSwedish Energy AgencyKnut and Alice Wallenberg Foundation
    Available from: 2017-04-18 Created: 2017-04-18 Last updated: 2017-10-03
  • 4.
    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, 364-370 p.Article 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.

  • 5.
    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, 485104- p.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. 

  • 6.
    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.

  • 7.
    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.

  • 8.
    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, 1421-1425 p.Article 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.

  • 9.
    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.

  • 10.
    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, 2843-2849 p.Article 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.

  • 11.
    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, 170-178 p.Article 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.

  • 12.
    Platzer-Björkman, Charlotte
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Frisk, Christoper
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsen, Jes
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Ericson, Tove
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Li, Shuyi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scragg, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Keller, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Törndahl, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Reduced interface recombination in Cu2ZnSnS4 solar cells with atomic layer deposition Zn1-xSnxO buffer layers2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, no 24, 243904Article in journal (Refereed)
    Abstract [en]

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

  • 13.
    Ren, Yi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scragg, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Frisk, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Larsen, Jes
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Li, Shuyi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer-Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Influence of the Cu2ZnSnS4 absorberthickness on thin film solar cells2015In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 212, no 12, 2889-2896 p.Article in journal (Refereed)
    Abstract [en]

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

  • 14.
    Szaniawski, Piotr
    et al.
    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.
    Frisk, Christopher
    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.
    Ledinek, Dorothea
    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.
    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.
    A Systematic Study of Light-On-Bias Behavior in Cu(In,Ga)Se2 Solar Cells With Varying Absorber Compositions2017In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 7, no 3, 882-891 p.Article in journal (Refereed)
    Abstract [en]

    Light-on-bias effects were investigated in multiple Cu(In, Ga)Se2 solar cells with varying absorber layer compositions. A strong link between deformations caused by red-on-bias treatments in current-voltage (IV ) and capacitance-voltage (CV) characteristics was demonstrated. Similarly to red-on-bias, blue-on-bias leads to a local increase in static negative charge, but in samples with CdS buffers this increase is shifted away from the interface and has no impact on device performance. IV characteristics of samples with Cd-free buffers are not affected by any light-on-bias treatments, suggesting that CdS plays a vital role in the decreased performance after red-on-bias. A statistical approach was used to search for compositional trends in red-on-bias behavior. Deformation factors were defined for IV and CV characteristics before and after the treatment. While there is a strong relationship between the deformations observed in both types of measurements, the degree to which red-on-bias affects IV and CV curves can vary dramatically. These variations cannot be attributed to changes in composition, since no clear compositional trends were found. Rather, other factors related to sample manufacturing and to the buffer layer seem to have major impact on red-on-bias behavior.

  • 15.
    Vermang, Bart
    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.
    Donzel-Gargand, Olivier
    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.
    Joel, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Salome, Pedro
    Borme, Jerome
    Sadeswasser, Sascha
    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.
    Rear Surface Optimization of CZTS Solar Cellsby Use of a Passivation Layer WithNanosized Point Openings2015In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403Article in journal (Refereed)
  • 16.
    Vermang, Bart
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. Uppsala Univ, Angstrom Solar Ctr, S-75121 Uppsala, Sweden.;Univ Leuven, Dept Elect Engn, B-3001 Leuven, Belgium.;IMEC, Thin Film Photovolta, B-3001 Leuven, Belgium..
    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.
    Frisk, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Joel, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Salome, Pedro
    Int Iberian Nanotechnol Lab, Lab Nanostruct Solar Cells, P-4715330 Braga, Portugal..
    Borme, Jerome
    Int Iberian Nanotechnol Lab, Lab Nanostruct Solar Cells, P-4715330 Braga, Portugal..
    Sadewasser, Sascha
    Int Iberian Nanotechnol Lab, Lab Nanostruct Solar Cells, P-4715330 Braga, Portugal..
    Platzer-Bjorkman, 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.
    Rear Surface Optimization of CZTS Solar Cells by Use of a Passivation Layer With Nanosized Point Openings2016In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 6, no 1, 332-336 p.Article in journal (Refereed)
    Abstract [en]

    Previously, an innovative way to reduce rear interface recombination in Cu(In, Ga)(S, Se)(2) (CIGSSe) solar cells has been successfully developed. In this work, this concept is established in Cu-2(Zn, Sn)(S, Se)(4) (CZTSSe) cells to demonstrate its potential for other thin-film technologies. Therefore, ultrathin CZTS cells with an Al2O3 rear surface passivation layer having nanosized point openings are fabricated. The results indicate that introducing such a passivation layer can have a positive impact on open-circuit voltage (V-OC; +17% rel.), short-circuit current (J(SC); +5% rel.), and fill factor (FF; +9% rel.), compared with corresponding unpassivated cells. Hence, a promising efficiency improvement of 32% rel. is obtained for the rear passivated cells.

  • 17.
    Vermang, Bart
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. Univ Leuven, Dept Elect Engn, B-3001 Leuven, Belgium..
    Ren, Yi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Joel, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Frisk, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Donzel-Gargand, Olivier
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Salome, Pedro
    Int Iberian Nanotechnol Lab, Nanostruct Solar Cells, P-4715330 Braga, Portugal..
    Borme, Jerome
    Int Iberian Nanotechnol Lab, Nanostruct Solar Cells, P-4715330 Braga, Portugal..
    Sadewasser, Sascha
    Int Iberian Nanotechnol Lab, Nanostruct Solar Cells, P-4715330 Braga, Portugal..
    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.
    Rear surface optimization of CZTS solar cells by use of a passivation layer with nano-sized point openings2015In: 2015 IEEE 42ND PHOTOVOLTAIC SPECIALIST CONFERENCE (PVSC), 2015Conference paper (Refereed)
    Abstract [en]

    Previously, an innovative way to reduce rear interface recombination of Cu(In,Ga)(S,Se)(2) (CIGSSe) solar cells has been successfully developed. In this work, this concept is established in Cu-2(Zn,Sn)(S,Se)(4) (CZTSSe) cells, to demonstrate its potential for other thin-film technologies. Therefore, ultra-thin CZTS cells with an Al2O3 rear surface passivation layer having nano-sized point openings are fabricated. The results indicate that introducing such a passivation layer can have a positive impact on open circuit voltage (V-OC; +49%(rel.)) or short circuit current (J(SC); +17%(rel.)), compared to corresponding unpassivated cells. Hence, a promising efficiency improvement of 52%(rel.) is obtained for the rear passivated cells.

  • 18.
    Vermang, Bart
    et al.
    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.
    Frisk, Christopher
    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.
    Rostvall, Fredrik
    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.
    Salomé, Pedro
    Borme, Jérome
    Nicoara, Nicoleta
    Sadewasser, Sascha
    Introduction of Si PERC Rear Contacting Designto Boost Efficiency of Cu(In,Ga)Se2 Solar Cells2014In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 4, no 6, 1644-1649 p.Article in journal (Refereed)
    Abstract [en]

    Recently, Cu(In,Ga)Se-2 (CIGS) solar cells have achieved 21% world-record efficiency, partly due to the introduction of a postdeposition potassium treatment to improve the front interface of CIGS absorber layers. However, as high-efficiency CIGS solar cells essentially require long diffusion lengths, the highly recombinative rear of these devices also deserves attention. In this paper, an Al2O3 rear surface passivation layer with nanosized local point contacts is studied to reduce recombination at the standard Mo/CIGS rear interface. First, passivation layers with well-controlled grids of nanosized point openings are established by use of electron beam lithography. Next, rear-passivated CIGS solar cells with 240-nm-thick absorber layers are fabricated as study devices. These cells show an increase in open-circuit voltage (+57 mV), short-circuit current (+3.8 mA/cm(2)), and fill factor [9.5% (abs.)], compared with corresponding unpassivated reference cells, mainly due to improvements in rear surface passivation and rear internal reflection. Finally, solar cell capacitance simulator (SCAPS) modeling is used to calculate the effect of reduced back contact recombination on high-efficiency solar cells with standard absorber layer thickness. The modeling shows that up to 50-mV increase in open-circuit voltage is anticipated.

1 - 18 of 18
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