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  • 1.
    Cunha, J. M. V.
    et al.
    Int Iberian Nanotechnol Lab, P-4715330 Braga, Portugal.
    Fernandes, P. A.
    Univ Aveiro, I3N, P-3810193 Aveiro, Portugal;Int Iberian Nanotechnol Lab, P-4715330 Braga, Portugal;Inst Politecn Porto, Inst Super Engn Porto, Dept Fis, CIETI, P-4200072 Porto, Portugal.
    Hultqvist, Adam
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Teixeira, J. P.
    Univ Aveiro, I3N, P-3810193 Aveiro, Portugal;Univ Aveiro, Dept Fis, P-3810193 Aveiro, Portugal.
    Bose, S.
    Int Iberian Nanotechnol Lab, P-4715330 Braga, Portugal.
    Vermang, B.
    IMEC Partner Solliance, B-3001 Leuven, Belgium;Univ Hasselt Partner Solliance, B-3590 Diepenbeek, Belgium;IMOMEC Partner Solliance, B-3590 Diepenbeek, Belgium.
    Garud, S.
    IMEC Partner Solliance, B-3001 Leuven, Belgium;Univ Hasselt Partner Solliance, B-3590 Diepenbeek, Belgium;IMOMEC Partner Solliance, B-3590 Diepenbeek, Belgium.
    Buldu, D.
    IMEC Partner Solliance, B-3001 Leuven, Belgium;Univ Hasselt Partner Solliance, B-3590 Diepenbeek, Belgium;IMOMEC Partner Solliance, B-3590 Diepenbeek, Belgium.
    Gaspar, J.
    Int Iberian Nanotechnol Lab, P-4715330 Braga, Portugal.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Leitao, J. P.
    Univ Aveiro, I3N, P-3810193 Aveiro, Portugal;Univ Aveiro, Dept Fis, P-3810193 Aveiro, Portugal.
    Salome, P. M. P.
    Int Iberian Nanotechnol Lab, P-4715330 Braga, Portugal;Univ Aveiro, Dept Fis, P-3810193 Aveiro, Portugal.
    Insulator Materials for Interface Passivation of Cu(In,Ga)Se-2 Thin Films2018In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 8, no 5, p. 1313-1319Article in journal (Refereed)
    Abstract [en]

    In this work, metal-insulator-semiconductor structures were fabricated in order to study different types of insulators, namely, aluminum oxide (Al2O3), silicon nitride, and silicon oxide (SiOx) to be used as passivation layers in Cu(In,Ga)Se-2 (CIGS) thin-film solar cells. The investigated stacks consisted of SLG/Mo/CIGS/insulator/Al. Raman scattering and photoluminescence measurements were done to verify the insulator deposition influence on the CIGS surface. In order to study the electrical properties of the CIGS-insulator interface, capacitance versus conductance and voltage (C-G-V) measurements were done to estimate the number and polarity of fixed insulator charges (Q(f)). The density of interface defects (D-it) was estimated from capacitance versus conductance and frequency (C-G-f) measurements. This study evidences that the deposition of the insulators at high temperatures (300 degrees C) and the use of a sputtering technique cause surface modification on the CIGS surface. We found that, by varying the SiOx deposition parameters, it is possible to have opposite charges inside the insulator, which would allow its use in different device architectures. The material with lower Dit values was Al2O3 when deposited by sputtering.

  • 2.
    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.

  • 3.
    Fjällström, Viktor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Salome, P. M. P.
    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.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Jarmar, T.
    Aitken, B. G.
    Zhang, K.
    Fuller, K.
    Williams, C. Kosik
    Potential-Induced Degradation of CuIn1-xGaxSe2 Thin Film Solar Cells2013In: IEEE Journal of Photovoltaics, ISSN 2156-3381, Vol. 3, no 3, p. 1090-1094Article in journal (Refereed)
    Abstract [en]

    The use of Na-free or low Na content glass substrates is observed to enhance the resiliency to potential-induced degradation, as compared with glass substrates with high Na content, such as soda lime glass (SLG). The results from stress tests in this study suggest that degradation caused by a combination of heat and bias across the SLG substrate is linked to increased Na concentration in the CdS and Cu(In,Ga)Se-2 (CIGS) layers in CIGS-based solar cells. The degradation during the bias stress is dramatic. The efficiency drops to close to 0% after 50 h of stressing. On the other hand, cells on Na-free and low Na content substrates exhibited virtually no efficiency degradation. The degraded cells showed partial recovery by resting at room temperature without bias; thus, the degradation is nonpermanent and may be due to Na migration and accumulation rather than chemical reaction.

  • 4.
    Hultqvist, Adam
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Cadmium Free Buffer Layers and the Influence of their Material Properties on the Performance of Cu(In,Ga)Se2 Solar Cells2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    CdS is conventionally used as a buffer layer in Cu(In,Ga)Se2, CIGS, solar cells. The aim of this thesis is to substitute CdS with cadmium-free, more transparent and environmentally benign alternative buffer layers and to analyze how the material properties of alternative layers affect the solar cell performance. The alternative buffer layers have been deposited using Atomic Layer Deposition, ALD. A theoretical explanation for the success of CdS is that its conduction band, Ec, forms a small positive offset with that of CIGS.

    In one of the studies in this thesis the theory is tested experimentally by changing both the Ec position of the CIGS and of Zn(O,S) buffer layers through changing their gallium and sulfur contents respectively. Surprisingly, the top performing solar cells for all gallium contents have Zn(O,S) buffer layers with the same sulfur content and properties in spite of predicted unfavorable Ec offsets. An explanation is proposed based on observed non-homogenous composition in the buffer layer.

    This thesis also shows that the solar cell performance is strongly related to the resistivity of alternative buffer layers made of (Zn,Mg)O. A tentative explanation is that a high resistivity reduces the influence of shunt paths at the buffer layer/absorber interface. For devices in operation however, it seems beneficial to induce persistent photoconductivity, by light soaking, which can reduce the effective Ec barrier at the interface and thereby improve the fill factor of the solar cells.

    Zn-Sn-O is introduced as a new buffer layer in this thesis. The initial studies show that solar cells with Zn-Sn-O buffer layers have comparable performance to the CdS reference devices.

    While an intrinsic ZnO layer is required for a high reproducibility and performance of solar cells with CdS buffer layers it is shown in this thesis that it can be thinned if Zn(O,S) or omitted if (Zn,Mg)O buffer layers are used instead. As a result, a top conversion efficiency of 18.1 % was achieved with an (Zn,Mg)O buffer layer, a record for a cadmium and sulfur free CIGS solar cell.

    List of papers
    1. Optimization of ALD-(Zn,Mg)O buffer layers and (Zn,Mg)O/Cu(In,Ga)Se-2 interfaces for thin film solar cells
    Open this publication in new window or tab >>Optimization of ALD-(Zn,Mg)O buffer layers and (Zn,Mg)O/Cu(In,Ga)Se-2 interfaces for thin film solar cells
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    2007 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 15, p. 6024-6027Article in journal (Refereed) Published
    Abstract [en]

    (Zn,Mg)O films, fabricated by atomic layer deposition, ALD, are investigated as buffer layers in Cu(In,Ga)Se2-based thin film solar cells. Optimization of the buffer layer is performed in terms of thickness, deposition temperature and composition. High efficiency devices are obtained for deposition at 105–135 °C, whereas losses in open circuit voltage are observed at higher deposition temperatures. The optimal compositional region for (Zn,Mg)O buffer layers in this study is for Mg/(Zn + Mg) contents of about 0.1–0.2, giving band gap values of 3.5–3.7 eV. These devices appear insensitive to thickness variations between 80 and 600 nm. Efficiencies of up to 16.2% are obtained for completely Cd- and S-free devices with (Zn,Mg)O buffer layers deposited with 1000 cycles at 120 °C and having a band gap of 3.6 eV.

    Keywords
    (Zn, Mg)O, Buffer layer, Cu(In, Ga)Se2, Solar cells
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-10910 (URN)10.1016/j.tsf.2006.12.047 (DOI)000246831600059 ()
    Available from: 2007-05-03 Created: 2007-05-03 Last updated: 2017-12-11Bibliographically approved
    2. Optimization of i-ZnO window layers for Cu(In,Ga)Se2 solar cells with ALD buffers
    Open this publication in new window or tab >>Optimization of i-ZnO window layers for Cu(In,Ga)Se2 solar cells with ALD buffers
    Show others...
    2007 (English)Conference paper, Published paper (Refereed)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-12392 (URN)
    Conference
    Proceedings of the 22nd European Photovoltaic Solar Energy Conference, Milano, 2007 : 3BV.5.18
    Available from: 2007-12-17 Created: 2007-12-17 Last updated: 2016-04-07Bibliographically approved
    3. CuGaSe2 solar cells using atomic layer deposited Zn(O,S) and (Zn,Mg)O buffer layers
    Open this publication in new window or tab >>CuGaSe2 solar cells using atomic layer deposited Zn(O,S) and (Zn,Mg)O buffer layers
    Show others...
    2009 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 517, no 7, p. 2305-2308Article in journal (Refereed) Published
    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.

    Keywords
    Solar cells, CuGaSe2, Buffer layer, (Zn, Mg)O, Zn(O, S), ALD
    National Category
    Physical Sciences Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-110983 (URN)10.1016/j.tsf.2008.10.109 (DOI)000263847300047 ()
    Note

    0040-6090 doi: DOI: 10.1016/j.tsf.2008.10.109

    Available from: 2009-12-01 Created: 2009-12-01 Last updated: 2017-12-12Bibliographically approved
    4. The effect of Zn1-xMgxO buffer layer deposition temperature on Cu(In,Ga)Se2 solar cells: A study of the buffer/absorber interface
    Open this publication in new window or tab >>The effect of Zn1-xMgxO buffer layer deposition temperature on Cu(In,Ga)Se2 solar cells: A study of the buffer/absorber interface
    Show others...
    2009 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 17, no 2, p. 115-125Article in journal (Refereed) Published
    Abstract [en]

    The effect of atomic layer deposition temperature of Zn1-xMgxO buffer   layers for Cu(In,Ga)Se-2 (CIGS) based solar cell devices is evaluated.   The Zn1-xMgxO films are grown using diethyl zinc, bis-cyclopentadienyl   magnesium and water as precursors in a temperature range of 105 to 180   C High efficiency devices are produced in the region front 105 up to   135 degrees C. At a Zn1-xMgxO deposition temperature of 120 C, a   maximum cell efficiency of 15.5% is reached by using a Zn1-xMgxO layer   with an x-value of 0.2 and a thickness of 140 inn. A significant drop   in cell efficiency due to large losses in open circuit voltage and fill   factor is observed for devices grown at temperatures above 150 C. No   differences in chemical composition, structure and morphology of the   samples are observed, except for the samples prepared at 105 and 120 C   that show elemental selenium present at the buffer/absorber interface.   The selenium at the interface does not lead to major degradation of   the,solar cell device efficiency. Instead, a decrease in Zn1-xMgxO   resistivity by more than one order of magnitude at growth temperatures   above 150 C may explain the degradation in solar cell performance. From   energy filtered transmission electron microscopy, the width of the   CIGS/Zn1-xMgxO chemical interface is found to be thinner than 10 not   without any areas of depletion for Cu, Se, Zn and O.

    Keywords
    Zn1-xMgxO, Cu(In, Ga)Se-2, interface, selenium, atomic layer deposition, resistivity
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-111352 (URN)10.1002/pip.859 (DOI)000263896800002 ()
    Available from: 2009-12-11 Created: 2009-12-11 Last updated: 2017-12-12Bibliographically approved
    5. Effects of CuIn0,5Ga0,5Se2 growth by isothermal and bithermal Cu-Poor/Rich/Poor sequence on solar cells properties
    Open this publication in new window or tab >>Effects of CuIn0,5Ga0,5Se2 growth by isothermal and bithermal Cu-Poor/Rich/Poor sequence on solar cells properties
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    2009 (English)In: 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, Published 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.

    Place, publisher, year, edition, pages
    Warrendale, PA: Material Research Society, 2009. p. 6
    Series
    Materials Research Society symposium proceedings, ISSN 0272-9172 ; 1165
    Keywords
    Solar Cell, Cu(In, Ga)Se2, buffer layer
    National Category
    Condensed Matter Physics Engineering and Technology
    Research subject
    Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-120587 (URN)10.1557/PROC-1165-M02-05 (DOI)
    Conference
    2009 MRS Spring Meeting, April 13 - 17, 2009, San Francisco, CA
    Available from: 2010-03-17 Created: 2010-03-15 Last updated: 2016-04-14Bibliographically approved
    6.
    The record could not be found. The reason may be that the record is no longer available or you may have typed in a wrong id in the address field.
    7. Growth and characterization of ZnO-based buffer layers for CIGS solar cells
    Open this publication in new window or tab >>Growth and characterization of ZnO-based buffer layers for CIGS solar cells
    2010 (English)In: Proceedings of the SPIE - The International Society for Optical Engineering: Oxide-based Materials and Devices / [ed] Teherani FH, Look DC, Litton CW, Rogers DJ, BELLINGHAM, WA, USA: SPIE-INT SOC OPTICAL ENGINEERING , 2010, p. 76030D-1-76030D-9Conference paper, Published paper (Refereed)
    Abstract [en]

    ZnO-based compounds are of interest as buffer layers in Cu(In,Ga)Se2 (CIGS) solar cells, due to the ability to change the electrical and optical properties of ZnO by addition of other elements. The device structure of a CIGS solar cell is; soda-lime glass/Mo/CIGS/buffer layer/ZnO/ZnO:Al. This contribution treats growth and characterization of Zn1-xMgxO and Zn(O,S) on glass substrates and as buffer layers in CIGS solar cell devices. The ZnO-based compounds are grown by atomic layer deposition at deposition temperatures below 200 °C using metal-organic precursors.

    Place, publisher, year, edition, pages
    BELLINGHAM, WA, USA: SPIE-INT SOC OPTICAL ENGINEERING, 2010
    Series
    Proceedings of SPIE-The International Society for Optical Engineering, ISSN 0277-786X ; 7603
    Keywords
    ZnO, buffer layer, Cu(In, Ga)Se-2, atomic layer deposition
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-133169 (URN)10.1117/12.846351 (DOI)000284035700007 ()978-0-8194-7999-0 (ISBN)
    Conference
    Conference on Oxide-based Materials and Devices San Francisco, CA, JAN 24-27, 2010
    Available from: 2010-11-02 Created: 2010-11-02 Last updated: 2016-04-18Bibliographically approved
    8. Experimental investigation of Cu(In1-x,Ga-x)Se-2/Zn(O1-z,S-z) solar cell performance
    Open this publication in new window or tab >>Experimental investigation of Cu(In1-x,Ga-x)Se-2/Zn(O1-z,S-z) solar cell performance
    2011 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 95, no 2, p. 497-503Article in journal (Refereed) Published
    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.

    Keywords
    Cu(In, Ga)Se2, buffer layer, interface, ZnO, ZnS, solar cell
    National Category
    Condensed Matter Physics Engineering and Technology
    Research subject
    Engineering Science with specialization in Solid State Physics; Engineering Science with specialization in Electronics
    Identifiers
    urn:nbn:se:uu:diva-133088 (URN)10.1016/j.solmat.2010.09.009 (DOI)000287006900013 ()
    Available from: 2010-11-02 Created: 2010-11-02 Last updated: 2017-12-12Bibliographically approved
    9. Evaluation of Zn-Sn-O buffer layers for CuIn0.5Ga0.5Se2 solar cells
    Open this publication in new window or tab >>Evaluation of Zn-Sn-O buffer layers for CuIn0.5Ga0.5Se2 solar cells
    2011 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 19, no 4, p. 478-481Article in journal (Refereed) Published
    Abstract [en]

    Thin Zn-Sn-O films are evaluated as new buffer layer material for Cu(In,Ga)Se-2-based solar cell devices. A maximum conversion efficiency of 13.8% (V-oc = 691 mV, J(sc)(QE) = 27.9 mA/cm(2), and FF = 71.6%) is reached for a solar cell using the Zn-Sn-O buffer layer which is comparable to the efficiency of 13.5% (V-oc - 706 mV, J(sc)(QE) - 26.3 mA/cm(2), and FF = 72.9%) for a cell using the standard reference CdS buffer layer. The open circuit voltage (V-oc) and the fill factor (FF) are found to increase with increasing tin content until an optimum in both parameters is reached for Sn/(Zn+Sn) values around 0.3-0.4.

    Keywords
    Zn-Sn-O, Cu(In, Ga)Se2, buffer layer, atomic layer deposition
    National Category
    Condensed Matter Physics Engineering and Technology
    Research subject
    Engineering Science with specialization in Solid State Physics; Engineering Science with specialization in Electronics
    Identifiers
    urn:nbn:se:uu:diva-133098 (URN)10.1002/pip.1039 (DOI)000290481100011 ()
    Available from: 2010-11-02 Created: 2010-11-02 Last updated: 2017-12-12Bibliographically approved
    10. Growth kinetics, properties, performance and stability of ALD Zn-Sn-O buffer layers for Cu(In,Ga)Se2 solar cells
    Open this publication in new window or tab >>Growth kinetics, properties, performance and stability of ALD Zn-Sn-O buffer layers for Cu(In,Ga)Se2 solar cells
    Show others...
    (English)Manuscript (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.

    Keywords
    Zn-Sn-O; Cu(In, Ga)Se2; buffer layer; atomic layer deposition
    National Category
    Condensed Matter Physics
    Research subject
    Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-133100 (URN)
    Available from: 2010-11-02 Created: 2010-11-02 Last updated: 2011-11-10
  • 5.
    Hultqvist, Adam
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Aitola, Kerttu
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Sveinbjörnsson, Kári
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Saki, Zahra
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Sharif Univ Technol, Tehran, Iran.
    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.
    Johansson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Atomic Layer Deposition of Electron Selective SnOx and ZnO Films on Mixed Halide Perovskite: Compatibility and Performance2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 35, p. 29707-29716Article in journal (Refereed)
    Abstract [en]

    The compatibility of atomic layer deposition directly onto the mixed halide perovskite formamidinium lead iodide:methylammonium lead bromide (CH(NH2)(2), CH3NH3)Pb(I,Br)(3) (FAPbI(3):MAPbBr(3)) perovskite films is investigated by exposing the perovskite films to the full or partial atomic layer deposition processes for the electron selective layer candidates ZnO and SnOx. Exposing the samples to the heat, the vacuum, and even the counter reactant of H2O of the atomic layer deposition processes does not appear to alter the perovskite films in terms of crystallinity, but the choice of metal precursor is found to be critical. The Zn precursor Zn(C2H5)(2) either by itself or in combination with H2O during the ZnO atomic layer deposition (ALD) process is found to enhance the decomposition of the bulk of the perovskite film into PbI2 without even forming ZnO. In contrast, the Sn precursor Sn(N(CH3)(2))(4) does not seem to degrade the bulk of the perovskite film, and conformal SnOx films can successfully be grown on top of it using atomic layer deposition. Using this SnOx film as the electron selective layer in inverted perovskite solar cells results in a lower power conversion efficiency of 3.4% than the 8.4% for the reference devices using phenyl-C-70-butyric acid methyl ester. However, the devices with SnOx show strong hysteresis and can be pushed to an efficiency of 7.8% after biasing treatments. Still, these cells lacks both open circuit voltage and fill factor compared to the references, especially when thicker SnOx films are used. Upon further investigation, a possible cause of these losses could be that the perovskite/SnOx interface is not ideal and more specifically found to be rich in Sn, O, and halides, which is probably a result of the nucleation during the SnOx growth and which might introduce barriers or alter the band alignment for the transport of charge carriers.

  • 6.
    Hultqvist, Adam
    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.
    Törndahl, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Evaluation of Zn-Sn-O buffer layers for CuIn0.5Ga0.5Se2 solar cells2011In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 19, no 4, p. 478-481Article in journal (Refereed)
    Abstract [en]

    Thin Zn-Sn-O films are evaluated as new buffer layer material for Cu(In,Ga)Se-2-based solar cell devices. A maximum conversion efficiency of 13.8% (V-oc = 691 mV, J(sc)(QE) = 27.9 mA/cm(2), and FF = 71.6%) is reached for a solar cell using the Zn-Sn-O buffer layer which is comparable to the efficiency of 13.5% (V-oc - 706 mV, J(sc)(QE) - 26.3 mA/cm(2), and FF = 72.9%) for a cell using the standard reference CdS buffer layer. The open circuit voltage (V-oc) and the fill factor (FF) are found to increase with increasing tin content until an optimum in both parameters is reached for Sn/(Zn+Sn) values around 0.3-0.4.

  • 7.
    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)
  • 8.
    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.

  • 9.
    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)
  • 10.
    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.

  • 11.
    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.

  • 12.
    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.

  • 13.
    Hultqvist, Adam
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Salomé, Pedro M. P.
    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.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Aitken, B.
    Zhang, K.
    Shi, Y.
    Fuller, K.
    Williams, C. Kosik
    Performance of Cu(In,Ga)Se-2 solar cells using nominally alkali free glass substrates with varying coefficient of thermal expansion2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 114, no 9, p. 094501-Article in journal (Refereed)
    Abstract [en]

    In this report, Cu(In,Ga)Se-2, CIGS, solar cell devices have been fabricated on nominally alkali free glasses with varying coefficients of thermal expansion (CTE) from 50 to 95* 10(-7)/degrees C. A layer of NaF deposited on top of the Mo was used to provide Na to the CIGS film. Increasing the glass CTE leads to a change of stress state of the solar cell stack as evidenced by measured changes of stress state of the Mo layer after CIGS deposition. The open circuit voltage, the short circuit current density, and the fill factors, for solar cells made on the various substrates, are all found to increase with CTE to a certain point. The median energy conversion efficiency values for 32 solar cells increases from 14.6% to the lowest CTE glass to 16.5% and 16.6%, respectively, for the two highest CTE glasses, which have CTE values closest to that of the soda lime glass. This is only slightly lower than the 17.0% median of soda lime glass reference devices. We propose a model where an increased defect density in the CIGS layer caused by thermal mismatch during cool-down is responsible for the lower efficiency for the low CTE glass substrates.

  • 14.
    Hultqvist, Adam
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. Stanford Univ, Dept Chem Engn, Stanford, CA 94305 USA..
    Sone, Takero
    Stanford Univ, Dept Chem Engn, Stanford, CA 94305 USA..
    Bent, Stacey F.
    Stanford Univ, Dept Chem Engn, Stanford, CA 94305 USA..
    Buffer Layer Point Contacts for CIGS Solar Cells Using Nanosphere Lithography and Atomic Layer Deposition2017In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 7, no 1, p. 322-328Article in journal (Refereed)
    Abstract [en]

    Point contacts provide an interesting approach for reducing the buffer layer/Cu(In, Ga)Se-2 interface recombination that typically limits Cu(In, Ga) Se-2 solar cell performance when nontoxic alternatives to CdS buffer layers are used. In this study, we implement a scheme to create a point contact buffer layer on Cu(In, Ga)Se-2 solar cells using a combination of atomic layer deposition and nanosphere lithography. While we showcase these buffer layers using Al2O3 as the passivating material, ZnO as the conductive material, and a silica nanosphere size of 310 nm in diameter, this scheme is general and could readily be applied for other materials and other sphere sizes. The resulting solar cells with Al2O3 and ZnO point contact buffer layers demonstrate successful application of this scheme, yielding a higher conversion efficiency (6.58 +/- 0.58%) than either of the binary buffer layers Al2O3 (0%) and ZnO (5.15 +/- 0.57%). The improvement over ZnO is mainly due to an increased open circuit voltage, which is an indication of a reduced surface recombination.

  • 15.
    Kapilashrami, Mukes
    et al.
    Advanced Light Source, Lawrence Berkeley National Laboratory, CA, USA.
    Kronawitter, Coleman X.
    Dept of Mechanical Engineering, University of California in Berkely, CA, och Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, CA, USA.
    Törndahl, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Lindahl, Johan
    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.
    Wang, Wei-Cheng
    Advanced Light Source, Lawrence Berkeley National Laboratory, CA, USA och Dept of Physics, Tamkang University, Tamsui, Taiwan, Kina.
    Chang, Ching-Lin
    Dept of Physics, Tamkang University, Tamsui, Taiwan, Kina.
    Mao, Samuel S.
    Dept of Mechanical Engineering, University of California in Berkely, CA, och Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, CA, USA.
    Guo, Jinghua
    Advanced Light Source, Lawrence Berkeley National Laboratory, CA, USA.
    Soft X-ray characterization of Zn1-xSnxOy electronic structure for thin film photovoltaics2012In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, no 29, p. 10154-10159Article in journal (Refereed)
    Abstract [en]

    Zinc tin oxide (Zn1-xSnxOy) has been proposed as an alternative buffer layer material to the toxic, and light narrow-bandgap CdS layer in CuIn1-x,GaxSe2 thin film solar cell modules. In this present study, synchrotron-based soft X-ray absorption and emission spectroscopies have been employed to probe the densities of states of intrinsic ZnO, Zn1-xSnxOy and SnOx thin films grown by atomic layer deposition. A distinct variation in the bandgap is observed with increasing Sn concentration, which has been confirmed independently by combined ellipsometry-reflectometry measurements. These data correlate directly to the open circuit potentials of corresponding solar cells, indicating that the buffer layer composition is associated with a modification of the band discontinuity at the CIGS interface. Resonantly excited emission spectra, which express the admixture of unoccupied O 2p with Zn 3d, 4s, and 4p states, reveal a strong suppression in the hybridization between the O 2p conduction band and the Zn 3d valence band with increasing Sn concentration.

  • 16.
    Lindahl, Johan
    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.
    Hultqvist, Adam
    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.
    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.
    The effect of Zn1−xSnxOy buffer layer thickness in 18.0% efficient Cd-free Cu(In,Ga)Se2 solar cells2013In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 21, no 8, p. 1588-1597Article in journal (Refereed)
    Abstract [en]

    The influence of the thickness of atomic layer deposited Zn1−xSnxOy buffer layers and the presence of an intrinsic ZnO layer on the performance of Cu(In,Ga)Se2 solar cells are investigated. The amorphous Zn1−xSnxOy layer, with a [Sn]/([Sn] + [Zn]) composition of approximately 0.18, forms a conformal and in-depth uniform layer with an optical band gap of 3.3 eV. The short circuit current for cells with a Zn1−xSnxOy layer are found to be higher than the short circuit current for CdS buffer reference cells and thickness independent. On the contrary, both the open circuit voltage and the fill factor values obtained are lower than the references and are thickness dependent. A high conversion efficiency of 18.0%, which is comparable with CdS references, is attained for a cell with a Zn1−xSnxOy layer thickness of approximately 13 nm and with an i-ZnO layer.

  • 17.
    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.

  • 18.
    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.

  • 19.
    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.

  • 20.
    Pettersson, Jonas
    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.
    Hultqvist, Adam
    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.
    The Influence of Absorber Thickness on Cu(In,Ga)Se-2 Solar Cells With Different Buffer Layers2013In: IEEE Journal of Photovoltaics, ISSN 2156-3381, Vol. 3, no 4, p. 1376-1382Article in journal (Refereed)
    Abstract [en]

    This study investigates the interplay between the absorber layer of Cu(In,Ga)Se-2 solar cells and the other layers of these devices. Cu(In, Ga)Se-2 devices with absorbers of different thicknesses and different buffer layers are fabricated. Absorber layers and finished devices are characterized. Good efficiencies are obtained, also for devices of substandard thickness down to 0.3 mu m. Best open-circuit voltages and fill factors are found for cells with half the standard absorber thickness, but the highest efficiencies are found for cells with the standard thickness of 1.6 mu m due to their higher short-circuit current density. Cu(In, Ga)Se-2 cells with Zn(O,S) buffer layers are more efficient than CdS reference devices for the same absorber thickness due to a higher short-circuit current. For cells with thin absorber layers, a part of the higher current is caused by higher quantum efficiency at long wavelengths. Electrical simulations indicate that the loss in the open-circuit voltage for the thinnest devices is due to recombination in the back contact region. The difference in long-wavelength quantum efficiency between the buffer layers is attributed to a difference in the CIGS band bending. Acceptors at the Cu(In, Ga)Se-2-CdS interface are proposed as an explanation for this difference. A low-quality back contact region enhances the effect.

  • 21.
    Platzer Björkman, Charlotte
    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.
    Hultqvist, Adam
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kessler, John
    Université de Nantes.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Optimization of ALD-(Zn,Mg)O buffer layers and (Zn,Mg)O/Cu(In,Ga)Se-2 interfaces for thin film solar cells2007In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 15, p. 6024-6027Article in journal (Refereed)
    Abstract [en]

    (Zn,Mg)O films, fabricated by atomic layer deposition, ALD, are investigated as buffer layers in Cu(In,Ga)Se2-based thin film solar cells. Optimization of the buffer layer is performed in terms of thickness, deposition temperature and composition. High efficiency devices are obtained for deposition at 105–135 °C, whereas losses in open circuit voltage are observed at higher deposition temperatures. The optimal compositional region for (Zn,Mg)O buffer layers in this study is for Mg/(Zn + Mg) contents of about 0.1–0.2, giving band gap values of 3.5–3.7 eV. These devices appear insensitive to thickness variations between 80 and 600 nm. Efficiencies of up to 16.2% are obtained for completely Cd- and S-free devices with (Zn,Mg)O buffer layers deposited with 1000 cycles at 120 °C and having a band gap of 3.6 eV.

  • 22.
    Platzer-Björkman, Charlotte
    et al.
    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.
    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.
    Band gap engineering of ZnO for high efficiency CIGS based solar cells2010In: Oxide-based Materials and Devices / [ed] Teherani FH, Look DC, Litton CW, Rogers DJ, 2010, Vol. 7603, p. 76030-76039Conference paper (Refereed)
    Abstract [en]

    Thin film solar cells based on Cu(In,Ga)Se2, called CIGS, is one of the most promising technologies for low cost, high efficiency photovoltaics. The CIGS device is composed of four layers; molybdenum back contact, CIGS p-type absorber, n-type buffer layer and doped ZnO top contact. The most common buffer layer is CdS, however it is desirable to find a Cd-free, large band gap alternative. In this paper, the use of ZnO-based buffer layers deposited by atomic layer deposition, ALD is described. Efficiencies of over 18% are shown by using Zn(O,S) or (Zn,Mg)O by ALD followed by sputtered ZnO:Al. The role of the conduction band alignment across the heterojunction is discussed, and results for large band gap CuGaSe2 absorbers are presented. In addition, light-soaking effects for devices with (Zn,Mg)O-based buffer layers are related to measurements of persistent photoconductivity of ALD-(Zn,Mg)O thin films.

  • 23.
    Salome, Pedro M. P.
    et al.
    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.
    Szaniawski, Piotr
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Leitao, Joaquim P.
    Hultqvist, Adam
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Fernandes, Paulo A.
    Teixeira, Jennifer P.
    Falcao, Bruno P.
    Zimmermann, Uwe
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    da Cunha, Antonio F.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    A comparison between thin film solar cells made from co-evaporated CuIn1-xGaxSe2 using a one-stage process versus a three-stage process2015In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 23, no 4, p. 470-478Article in journal (Refereed)
    Abstract [en]

    Until this day, the most efficient Cu(In,Ga)Se-2 thin film solar cells have been prepared using a rather complex growth process often referred to as three-stage or multistage. This family of processes is mainly characterized by a first step deposited with only In, Ga and Se flux to form a first layer. Cu is added in a second step until the film becomes slightly Cu-rich, where-after the film is converted to its final Cu-poor composition by a third stage, again with no or very little addition of Cu. In this paper, a comparison between solar cells prepared with the three-stage process and a one-stage/in-line process with the same composition, thickness, and solar cell stack is made. The one-stage process is easier to be used in an industrial scale and do not have Cu-rich transitions. The samples were analyzed using glow discharge optical emission spectroscopy, scanning electron microscopy, X-ray diffraction, current-voltage-temperature, capacitance-voltage, external quantum efficiency, transmission/reflection, and photoluminescence. It was concluded that in spite of differences in the texturing, morphology and Ga gradient, the electrical performance of the two types of samples is quite similar as demonstrated by the similar J-V behavior, quantum spectral response, and the estimated recombination losses. 

  • 24.
    Salome, Pedro M. P.
    et al.
    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.
    Fjällström, Viktor
    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.
    Aitken, B. G.
    Zhang, K.
    Fuller, K.
    Williams, C. Kosik
    Incorporation of Na in Cu(In,Ga)Se-2 Thin-Film Solar Cells: A Statistical Comparison Between Na From Soda-Lime Glass and From a Precursor Layer of NaF2014In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 4, no 6, p. 1659-1664Article in journal (Refereed)
    Abstract [en]

    The presence of Na in Cu(In,Ga)Se-2 layers increases the electrical performance of this type of thin- film solar cell. A detailed comparison of incorporating Na in the CIGS layer by two different methods is performed by evaluating several hundred devices fabricated under similar conditions. The firstmethod is based on the conventionally used Na diffusion from the soda-lime glass substrate, whereas the second method is based on a NaF precursor layer deposited on a Mo- coated alkali- free glass substrate. The sample where Na is introduced by using a NaF precursor layer shows an orientation weighted toward (2 0 4)/(2 2 0) and a net acceptor concentration of 3.4 x 10(16) cm(-3), while SLG shows a (1 1 2) orientation with a 2.9 x 10(16) cm(-3) acceptor concentration. Both sample types show close identical elemental depth profiles, morphology, and electrical performance.

  • 25.
    Salome, Pedro M. P.
    et al.
    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.
    Fjällström, Viktor
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Vermang, Bart
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Aitken, B.
    Zhang, K.
    Fuller, K.
    Williams, C. Kosik
    The effect of high growth temperature on Cu(In,Ga)Se-2 thin film solar cells2014In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 123, p. 166-170Article in journal (Refereed)
    Abstract [en]

    The morphological, elemental distribution and electrical performance effects of increasing the Cu(In,Ga) Se-2 (CIGS) growth substrate temperature are studied. While the increased substrate growth temperature with no other modifications led to increased CIGS grain size, it also resulted in depth profile flattening of the [Ga]/([Ga]+[In]) ratio. Tuning the Ga profile in the high temperature process led to a more desirable [Ga]/([Ga]+[In]) depth profile and allowed a comparison between high and standard temperature. Devices prepared at higher temperature showed an improved grain size and the electrical performance is very similar to that of the reference sample prepared at a standard temperature.

  • 26.
    Salomé, Pedro
    et al.
    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.
    Hultqvist, Adam
    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.
    Na doping of CIGS solar cells using low sodium-doped mo layer2013In: IEEE Journal of Photovoltaics, ISSN 2156-3381, Vol. 3, no 1, p. 509-513Article in journal (Refereed)
    Abstract [en]

    Na plays an important role in the electrical performance of Cu(In,Ga)Se2 (CIGS) thin-film solar cells. Traditionally, Na has been introduced during the growth of CIGS by thermal diffusion from the soda-lime glass (SLG) substrate; however, better control of the amount of Na is needed to have a more precise control of growth conditions. The introduction of Na into CIGS was studied in three different ways: from the SLG, from a NaF precursor, and from a Na-doped Mo (MoNa) back contact. The most successful approaches were obtained by using the conventional SLG and the NaF precursor. Different growth temperatures of CIGS were tested in an attempt to diffuse more Na from the MoNa layer.

  • 27.
    Salomé, Pedro M. P.
    et al.
    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.
    Hultqvist, Adam
    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.
    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.
    The effect of Mo back contact ageing on Cu(In,Ga)Se-2 thin-film solar cells2014In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 22, no 1, p. 83-89Article in journal (Refereed)
    Abstract [en]

    In this work, we investigate the effect of ageing Mo-coated substrates in a dry and N-2 flooded cabinet. The influence was studied by preparing Cu(In,Ga)Se-2 solar cells and by comparing the electrical performance with devices where the Mo layer was not aged. The measurements used for this study were current-voltage (J-V), external quantum efficiency (EQE), secondary ion mass spectroscopy (SIMS) and capacitance-voltage (C-V). It was concluded that devices prepared with the aged Mo layer have, in average, an increase of 0.8% in efficiency compared with devices that had a fresh Mo layer. Devices with aged Mo exhibited a nominal increase of 12.5mV of open circuit voltage, a decrease of 1.1mA/cm(-2) of short circuit current and a fill factor increase of 2.4%. Heat treatment of fresh Mo layers in oxygen atmosphere was also studied as an alternative to ageing and was shown to provide a similar effect to the aged device's performance. 

  • 28.
    Salomé, Pedro M. P.
    et al.
    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.
    Fjällström, Viktor
    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.
    Aitken, B.
    Vaidyanathan, K.
    Zhang, K.
    Fuller, K.
    Williams, C. Kosik
    Cu(In,Ga)Se-2 Solar Cells With Varying Na Content Prepared on Nominally Alkali-Free Glass Substrates2013In: IEEE Journal of Photovoltaics, ISSN 2156-3381, Vol. 3, no 2, p. 852-858Article in journal (Refereed)
    Abstract [en]

    In this paper, Cu(In,Ga)Se-2 (CIGS) thin-film solar cells are prepared on nominally alkali-free glass substrates using an in-line CIGS growth process. As compared with, for example, borosilicate glass or quartz, the glass is engineered to have similar thermal expansion coefficient as soda-lime glass (SLG) but with alkali content close to zero. Na is incorporated in the CIGS material using an ex-situ deposited NaF precursor layer evaporated onto the Mo back contact. Several thicknesses of the NaF layer were tested. The results show that there is a process window, between 15 and 22.5 nm NaF, where the solar cell conversion efficiency is comparable with or exceeding that of SLG references. The effect of an NaF layer that is too thin on the solar cell parameters was mainly lowering the open-circuit voltage, which points to a lower effective dopant concentration in the CIGS layer and is also consistent with presented C-V measurements and modeling results. For excessively thick NaF layers, delamination of the CIGS layer occurred. Additional measurements, such as scanning electron microscopy (SEM), secondary ion mass spectrometry, capacitance-voltage analysis (C-V), time-resolved photoluminescence (TRPL), external quantum efficiency (EQE), current-voltage analysis (J-V), and modeling, are presented, and the results are discussed.

  • 29.
    Törndahl, Tobias
    et al.
    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, Experimental Physics.
    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.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    The effect of Zn1-xMgxO buffer layer deposition temperature on Cu(In,Ga)Se2 solar cells: A study of the buffer/absorber interface2009In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 17, no 2, p. 115-125Article in journal (Refereed)
    Abstract [en]

    The effect of atomic layer deposition temperature of Zn1-xMgxO buffer   layers for Cu(In,Ga)Se-2 (CIGS) based solar cell devices is evaluated.   The Zn1-xMgxO films are grown using diethyl zinc, bis-cyclopentadienyl   magnesium and water as precursors in a temperature range of 105 to 180   C High efficiency devices are produced in the region front 105 up to   135 degrees C. At a Zn1-xMgxO deposition temperature of 120 C, a   maximum cell efficiency of 15.5% is reached by using a Zn1-xMgxO layer   with an x-value of 0.2 and a thickness of 140 inn. A significant drop   in cell efficiency due to large losses in open circuit voltage and fill   factor is observed for devices grown at temperatures above 150 C. No   differences in chemical composition, structure and morphology of the   samples are observed, except for the samples prepared at 105 and 120 C   that show elemental selenium present at the buffer/absorber interface.   The selenium at the interface does not lead to major degradation of   the,solar cell device efficiency. Instead, a decrease in Zn1-xMgxO   resistivity by more than one order of magnitude at growth temperatures   above 150 C may explain the degradation in solar cell performance. From   energy filtered transmission electron microscopy, the width of the   CIGS/Zn1-xMgxO chemical interface is found to be thinner than 10 not   without any areas of depletion for Cu, Se, Zn and O.

  • 30.
    Törndahl, Tobias
    et al.
    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.
    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.
    Growth and characterization of ZnO-based buffer layers for CIGS solar cells2010In: Proceedings of the SPIE - The International Society for Optical Engineering: Oxide-based Materials and Devices / [ed] Teherani FH, Look DC, Litton CW, Rogers DJ, BELLINGHAM, WA, USA: SPIE-INT SOC OPTICAL ENGINEERING , 2010, p. 76030D-1-76030D-9Conference paper (Refereed)
    Abstract [en]

    ZnO-based compounds are of interest as buffer layers in Cu(In,Ga)Se2 (CIGS) solar cells, due to the ability to change the electrical and optical properties of ZnO by addition of other elements. The device structure of a CIGS solar cell is; soda-lime glass/Mo/CIGS/buffer layer/ZnO/ZnO:Al. This contribution treats growth and characterization of Zn1-xMgxO and Zn(O,S) on glass substrates and as buffer layers in CIGS solar cell devices. The ZnO-based compounds are grown by atomic layer deposition at deposition temperatures below 200 °C using metal-organic precursors.

  • 31.
    Zhang, Jinbao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Monash Univ, Dept Mat Engn, Clayton, Vic 3800, Australia.
    Hultqvist, Adam
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Tian
    Monash Univ, Dept Mat Engn, Clayton, Vic 3800, Australia.
    Jiang, Liangcong
    Monash Univ, Dept Mat Engn, Clayton, Vic 3800, Australia.
    Ruan, Changqing
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Yang, Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Cheng, Yibing
    Monash Univ, Dept Mat Engn, Clayton, Vic 3800, Australia.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Johansson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Al2O3 Underlayer Prepared by Atomic Layer Deposition for Efficient Perovskite Solar Cells.2017In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 10, no 19, p. 3810-3817Article in journal (Refereed)
    Abstract [en]

    Perovskite solar cells, as an emergent technology for solar energy conversion, have attracted much attention in the solar cell community by demonstrating impressive enhancement in power conversion efficiencies. However, the high temperature and manually processed TiO2 underlayer prepared by spray pyrolysis significantly limit the large-scale application and device reproducibility of perovskite solar cells. In this study, lowtemperature atomic layer deposition (ALD) is used to prepare a compact Al2 O3 underlayer for perovskite solar cells. The thickness of the Al2 O3 layer can be controlled well by adjusting the deposition cycles during the ALD process. An optimal Al2 O3 layer effectively blocks electron recombination at the perovskite/fluorine-doped tin oxide interface and sufficiently transports electrons through tunneling. Perovskite solar cells fabricated with an Al2 O3 layer demonstrated a highest efficiency of 16.2 % for the sample with 50 ALD cycles (ca. 5 nm), which is a significant improvement over underlayer-free PSCs, which have a maximum efficiency of 11.0 %. Detailed characterization confirms that the thickness of the Al2 O3 underlayer significantly influences the charge transfer resistance and electron recombination processes in the devices. Furthermore, this work shows the feasibility of using a high band-gap semiconductor such as Al2 O3 as the underlayer in perovskite solar cells and opens up pathways to use ALD Al2 O3 underlayers for flexible solar cells.

1 - 31 of 31
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