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Keller, J., Chalvet, F., Joel, J., Aijaz, A., Kubart, T., Riekehr, L., . . . Törndahl, T. (2018). Effect of KF absorber treatment on the functionality of different transparent conductive oxide layers in CIGSe solar cells. Progress in Photovoltaics, 26(1), 13-23
Open this publication in new window or tab >>Effect of KF absorber treatment on the functionality of different transparent conductive oxide layers in CIGSe solar cells
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2018 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 26, no 1, p. 13-23Article in journal (Refereed) Published
Abstract [en]

This contribution studies the impact of the KF-induced Cu(In,Ga)Se2 (CIGSe) absorber modification on the suitability of different transparent conductive oxide (TCO) layers in solar cells. The TCO material was varied between ZnO:Al (AZO), ZnO:B (BZO), and In2O3:H (IOH). It is shown that the thermal stress needed for optimized TCO properties can establish a transport barrier for charge carriers, which results in severe losses in fill factor (FF) for temperatures >150°C. The FF losses are accompanied by a reduction in open circuit voltage (Voc) that might originate from a decreased apparent doping density (Nd,app) after annealing. Thermally activated redistributions of K and Na in the vicinity of the CdS/(Cu,K)-In-Se interface are suggested to be the reason for the observed degradation in solar cell performance. The highest efficiency was measured for a solar cell where the absorber surface modification was removed and a BZO TCO layer was deposited at a temperature of 165°C. The presented results highlight the importance of well-designed TCO and buffer layer processes for CIGSe solar cells when a KF post deposition treatment (KF-PDT) was applied.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-332827 (URN)10.1002/pip.2925 (DOI)000418097200002 ()
Funder
Swedish Energy Agency, 2012-004591
Available from: 2017-11-02 Created: 2017-11-02 Last updated: 2018-01-17Bibliographically approved
Salome, P. M. P., Vermang, B., Ribeiro-Andrade, R., Teixeira, J. P., Cunha, J. M. V., Mendes, M. J., . . . Sadewasser, S. (2018). Passivation of Interfaces in Thin Film Solar Cells: Understanding the Effects of a Nanostructured Rear Point Contact Layer. Advanced Materials Interfaces, 5(2), Article ID 1701101.
Open this publication in new window or tab >>Passivation of Interfaces in Thin Film Solar Cells: Understanding the Effects of a Nanostructured Rear Point Contact Layer
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2018 (English)In: Advanced Materials Interfaces, ISSN 2196-7350, Vol. 5, no 2, article id 1701101Article in journal (Refereed) Published
Abstract [en]

Thin film solar cells based in Cu(In,Ga)Se-2 (CIGS) are among the most efficient polycrystalline solar cells, surpassing CdTe and even polycrystalline silicon solar cells. For further developments, the CIGS technology has to start incorporating different solar cell architectures and strategies that allow for very low interface recombination. In this work, ultrathin 350 nm CIGS solar cells with a rear interface passivation strategy are studied and characterized. The rear passivation is achieved using an Al2O3 nanopatterned point structure. Using the cell results, photoluminescence measurements, and detailed optical simulations based on the experimental results, it is shown that by including the nanopatterned point contact structure, the interface defect concentration lowers, which ultimately leads to an increase of solar cell electrical performance mostly by increase of the open circuit voltage. Gains to the short circuit current are distributed between an increased rear optical reflection and also due to electrical effects. The approach of mixing several techniques allows us to make a discussion considering the different passivation gains, which has not been done in detail in previous works. A solar cell with a nanopatterned rear contact and a 350 nm thick CIGS absorber provides an average power conversion efficiency close to 10%.

Keywords
Cu(In, Ga)Se-2 (CIGS), nanofabrication, passivation, photovoltaics, semiconductors, thin film solar cells
National Category
Physical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-343670 (URN)10.1002/admi.201701101 (DOI)000423173800013 ()
Funder
EU, Horizon 2020, 720887EU, European Research Council, 715027
Available from: 2018-03-07 Created: 2018-03-07 Last updated: 2018-06-14Bibliographically approved
Szaniawski, P., Olsson, J., Frisk, C., Fjällström, V., Ledinek, D., Larsson, F., . . . Edoff, M. (2017). A Systematic Study of Light-On-Bias Behavior in Cu(In,Ga)Se2 Solar Cells With Varying Absorber Compositions. IEEE Journal of Photovoltaics, 7(3), 882-891
Open this publication in new window or tab >>A Systematic Study of Light-On-Bias Behavior in Cu(In,Ga)Se2 Solar Cells With Varying Absorber Compositions
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2017 (English)In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 7, no 3, p. 882-891Article in journal (Refereed) Published
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.

Keywords
Capacitance;Charge measurement;Current measurement;Light emitting diodes;Lighting;Photovoltaic cells;Temperature measurement;Capacitance-voltage characteristics;current-voltage characteristics;degradation;deposition and characterization of thin film PV absorbers;photovoltaic cells;photovoltaic effects;thin film PV device properties and modeling
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-319426 (URN)10.1109/JPHOTOV.2017.2655148 (DOI)000399992000023 ()
Available from: 2017-04-04 Created: 2017-04-04 Last updated: 2017-05-30Bibliographically approved
Szaniawski, P., Zabierowski, P., Olsson, J., Zimmermann, U. & Edoff, M. (2017). Advancing the understanding of reverse breakdown in Cu(In,Ga)Se2 solar cells. IEEE Journal of Photovoltaics, 7(4), 1136-1142
Open this publication in new window or tab >>Advancing the understanding of reverse breakdown in Cu(In,Ga)Se2 solar cells
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2017 (English)In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 7, no 4, p. 1136-1142Article in journal (Refereed) Published
Abstract [en]

Reverse breakdown is investigated in multiple Cu(In,Ga)Se-2 solar cells with varying buffer layer thicknesses. A method to extract transition voltage, which marks the change of conduction mechanism that leads to electrical breakdown, is described as an alternative to the often less-meaningful breakdown voltage. Transition voltages for samples with CdS and ZnxSn1-xOy buffers are extracted from breakdown measurements performed in darkness and under illumination. The electric field is calculated for ZTO-based samples measured in darkness, and its implications for the energy band structure are examined. Fowler-Nordheim tunneling and Poole-Frenkel conduction are considered as candidates for the main breakdown mechanism in darkness. A model combining the two conduction mechanisms is proposed, and fits for experimental data are presented and discussed. Involvement of defects is debated, and defect-andbreakdown- related phenomena are showcased.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-319442 (URN)10.1109/JPHOTOV.2017.2699860 (DOI)000404258900027 ()
Available from: 2017-04-04 Created: 2017-04-04 Last updated: 2017-09-12Bibliographically approved
Zhang, J., Hultqvist, A., Zhang, T., Jiang, L., Ruan, C., Yang, L., . . . Johansson, E. (2017). Al2 O3 Underlayer Prepared by Atomic Layer Deposition for Efficient Perovskite Solar Cells.. ChemSusChem, 10(19), 3810-3817
Open this publication in new window or tab >>Al2 O3 Underlayer Prepared by Atomic Layer Deposition for Efficient Perovskite Solar Cells.
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2017 (English)In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 10, no 19, p. 3810-3817Article in journal (Refereed) Published
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.

Keywords
atomic layer deposition, electron transport, perovskites, semiconductors, solar cells
National Category
Nano Technology
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-336200 (URN)10.1002/cssc.201701160 (DOI)000412732900017 ()28857493 (PubMedID)
Funder
Swedish Energy AgencyÅForsk (Ångpanneföreningen's Foundation for Research and Development)Swedish Research CouncilSwedish Research Council FormasKnut and Alice Wallenberg Foundation
Available from: 2017-12-12 Created: 2017-12-12 Last updated: 2018-01-10Bibliographically approved
Bilousov, O. V., Ren, Y., Törndahl, T., Donzel-Gargand, O., Ericson, T., Platzer Björkman, C., . . . Hägglund, C. (2017). ALD of phase controlled tin monosulfide thin films. In: : . Paper presented at Joint EuroCVD 21 – Baltic ALD 15.
Open this publication in new window or tab >>ALD of phase controlled tin monosulfide thin films
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2017 (English)Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

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

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

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

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

Keywords
atomic layer deposition, thin films, solar cells, semiconductors
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-335501 (URN)
Conference
Joint EuroCVD 21 – Baltic ALD 15
Projects
Ultrathin nanocomposite absorbers and heterojunctions for solar cells
Funder
Swedish Research Council, 621-2014-5599
Available from: 2017-12-06 Created: 2017-12-06 Last updated: 2017-12-29Bibliographically approved
Bilousov, O. V., Ren, Y., Törndahl, T., Donzel-Gargand, O., Ericson, T., Platzer-Björkman, C., . . . Hägglund, C. (2017). Atomic Layer Deposition of Cubic and Orthorhombic Phase Tin Monosulfide. Chemistry of Materials, 29(7), 2969-2978
Open this publication in new window or tab >>Atomic Layer Deposition of Cubic and Orthorhombic Phase Tin Monosulfide
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2017 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 29, no 7, p. 2969-2978Article in journal (Refereed) Published
Abstract [en]

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

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2017
National Category
Chemical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-321836 (URN)10.1021/acs.chemmater.6b05323 (DOI)000399264100042 ()
Funder
Swedish Research Council, 621-2014-5599
Available from: 2017-05-15 Created: 2017-05-15 Last updated: 2017-05-15Bibliographically approved
Hultqvist, A., Aitola, K., Sveinbjörnsson, K., Saki, Z., Larsson, F., Törndahl, T., . . . Edoff, M. (2017). Atomic Layer Deposition of Electron Selective SnOx and ZnO Films on Mixed Halide Perovskite: Compatibility and Performance. ACS Applied Materials and Interfaces, 9(35), 29707-29716
Open this publication in new window or tab >>Atomic Layer Deposition of Electron Selective SnOx and ZnO Films on Mixed Halide Perovskite: Compatibility and Performance
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2017 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 35, p. 29707-29716Article in journal (Refereed) Published
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.

Keywords
perovskite solar cell, atomic layer deposition, interfaces, electron selective layers, precursor chemistry
National Category
Materials Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-335852 (URN)10.1021/acsami.7b07627 (DOI)000410597500034 ()28792724 (PubMedID)
Available from: 2018-01-25 Created: 2018-01-25 Last updated: 2018-02-12Bibliographically approved
Salome, P. M. P., Ribeiro-Andrade, R., Teixeira, J. P., Keller, J., Törndahl, T., Nicoara, N., . . . Sadewasser, S. (2017). Cd and Cu Interdiffusion in Cu(In, Ga) Se-2/CdS Hetero-Interfaces. IEEE Journal of Photovoltaics, 7(3), 858-863
Open this publication in new window or tab >>Cd and Cu Interdiffusion in Cu(In, Ga) Se-2/CdS Hetero-Interfaces
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2017 (English)In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 7, no 3, p. 858-863Article in journal (Refereed) Published
Abstract [en]

We report a detailed characterization of an industrylike prepared Cu(In, Ga) Se-2 (CIGS)/CdS heterojunction by scanning transmission electron microscopy and photoluminescence (PL). Energy dispersive X-ray spectroscopy shows the presence of several regions in the CIGS layer that are Cu deprived and Cd enriched, suggesting the segregation of Cd-Se. Concurrently, the CdS layer shows Cd-deprived regions with the presence of Cu, suggesting a segregation of Cu-S. The two types of segregations are always found together, which, to the best of our knowledge, is observed for the first time. The results indicate that there is a diffusion process that replaces Cu with Cd in the CIGS layer and Cd with Cu in the CdS layer. Using a combinatorial approach, we identified that this effect is independent of focused-ion beam sample preparation and of the transmission electron microscopy grid. Furthermore, PL measurements before and after an HCl etch indicate a lower degree of defects in the postetch sample, compatible with the segregates removal. We hypothesize that Cu2-x Se nanodomains react during the chemical bath process to form these segregates since the chemical reaction that dominates this process is thermodynamically favorable. These results provide important additional information about the formation of the CIGS/CdS interface.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2017
Keywords
CdS, Cu(In, Ga) Se-2 (CIGS), diffusion, solar cells, thin films, transmission electron microscopy (TEM)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-322689 (URN)10.1109/JPHOTOV.2017.2666550 (DOI)000399992000019 ()
Available from: 2017-05-29 Created: 2017-05-29 Last updated: 2017-05-29Bibliographically approved
Salome, P. M., Keller, J., Törndahl, T., Teixeira, J. P., Nicoara, N., Andrade, R.-R. -., . . . Sadewasser, S. (2017). CdS and Zn1-xSnxOy buffer layers for CIGS solar cells. Solar Energy Materials and Solar Cells, 159, 272-281
Open this publication in new window or tab >>CdS and Zn1-xSnxOy buffer layers for CIGS solar cells
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2017 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 159, p. 272-281Article in journal (Refereed) Published
Abstract [en]

Thin film solar cells based on Cu(In,Ga)Se-2 (CIGS), where just the buffer layer is changed, were fabricated and studied. The effects of two different buffer layers, CdS and Zn1-xSnxOy (ZnSnO), are compared using several characterization techniques. We compared both devices and observe that the ZnSnO-based solar cells have similar values of power conversion efficiency as compared to the cells with CdS buffer layers. The ZnSnO-based devices have higher values in the short-circuit current (6) that compensate for lower values in fill factor (FF) and open circuit voltage (V-oc) than CdS based devices. Kelvin probe force microscopy (KPFM) results indicate that CdS provides junctions with slightly higher surface photovoltage (SPV) than ZnSnO, thus explaining the lower Voc potential for the ZnSnO sample. The TEM analysis shows a poly-crystalline ZnSnO layer and we have not detected any strong evidence of diffusion of Zn or Sn into the CIGS. From the photoluminescence measurements, we concluded that both samples are being affected by fluctuating potentials, although this effect is higher for the CdS sample.

Keywords
Thin film solar cells, Cu(In, Ga)Se-2 (CIGS), Buffer layers, CdS, Zn1-xSnxOy
National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-310732 (URN)10.1016/j.solmat.2016.09.023 (DOI)000388053600032 ()
Funder
EU, European Research Council, 327367Swedish Energy Agency, 2012-004591VINNOVA, 2013-02199StandUp
Available from: 2016-12-20 Created: 2016-12-19 Last updated: 2017-11-29Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-4111-4613

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