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Törndahl, Tobias
Publications (10 of 70) Show all publications
Larsson, F., Donzel-Gargand, O., Keller, J., Edoff, M. & Törndahl, T. (2018). Atomic layer deposition of Zn(O,S) buffer layers for Cu(In,Ga)Se-2 solar cells with KF post-deposition treatment. Solar Energy Materials and Solar Cells, 183, 8-15
Open this publication in new window or tab >>Atomic layer deposition of Zn(O,S) buffer layers for Cu(In,Ga)Se-2 solar cells with KF post-deposition treatment
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2018 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 183, p. 8-15Article in journal (Refereed) Published
Abstract [en]

We investigate the possibility to combine Zn(O,S) buffer layers grown by atomic layer deposition (ALD) with KF post-deposition treated Cu(In,Ga)Se-2 (CIGS-KF) in solar cells. It is shown that the beneficial effect on open-circuit voltage from the post-deposition treatment is essentially independent of buffer layer material. However, a wet chemical surface treatment is required prior to ALD in order to achieve competitive fill factor values. A water rinse is sufficient to create an absorber surface similar to the one formed during a conventional CdS chemical bath deposition process. However, it is observed that CIGS-KF/Zn(O,S) devices made with water-rinsed absorbers systematically result in lower fill factor values than for the corresponding CIGS-KF/CdS references. This effect can be mitigated by decreasing the H2S:H2O precursor ratio during ALD initiation, indicating that the fill factor limitation is linked to the initial Zn(O,S) growth on the modified CIGS-KF surface. The best CIGS-KF/Zn (O,S) devices were fabricated by etching away the KF-modified surface layer prior to ALD, followed by a low temperature anneal. The thermal treatment step is needed to increase the open-circuit voltage close to the value of the CdS devices. The results presented in this contribution indicate that the main beneficial effects from KFPDT in our devices are neither associated with the CdS CBD process nor due to the formation of a K-In-Serich phase on the CIGS surface.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2018
Keywords
CIGS, KF-PDT, Zinc oxysulfide, Buffer layers, Interfaces
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-358259 (URN)10.1016/j.solmat.2018.03.045 (DOI)000435624400002 ()
Funder
Swedish Energy Agency, 2017-004796
Available from: 2018-08-27 Created: 2018-08-27 Last updated: 2018-08-27Bibliographically approved
Keller, J., Chen, W.-C., Riekehr, L., Kubart, T., Törndahl, T. & Edoff, M. (2018). Bifacial Cu(In,Ga)Se2 solar cells using hydrogen‐doped In2O3 films as a transparent back contact. Progress in Photovoltaics, 26(10), 846-858
Open this publication in new window or tab >>Bifacial Cu(In,Ga)Se2 solar cells using hydrogen‐doped In2O3 films as a transparent back contact
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2018 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 26, no 10, p. 846-858Article in journal (Refereed) Published
Abstract [en]

Hydrogen‐doped In2O3 (IOH) films are used as a transparent back contact in bifacial Cu(In,Ga)Se2 (CIGS) solar cells. The effect of the IOH thickness and the impact of the sodium incorporation technique on the photovoltaic parameters are studied, and clear correlations are observed. It is shown that a loss in short circuit current density (JSC) is the major limitation at back side illumination. The introduction of a thin Al2O3 layer on top of the IOH significantly increases the collection efficiency (ϕ(x)) for electrons generated close to the back contact. In this way, the JSC loss can be mitigated to only ~ 25% as compared with front side illumination. The Al2O3 film potentially reduces the interface defect density or, alternatively, creates a field effect passivation. In addition, it prevents the excessive formation of Ga2O3 at the CIGS/IOH interface, which is found otherwise when a NaF layer is added before absorber deposition. Consequently, detrimental redistributions in Ga and In close to the back contact can be avoided. Finally, a bifacial CIGS solar cell with an efficiency (η) of η = 11.0% at front and η = 6.0% at back side illumination could be processed. The large potential for further improvements is discussed.

National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-363288 (URN)10.1002/pip.3025 (DOI)000443696500008 ()
Funder
Swedish Energy Agency, 2016-008376Swedish Foundation for Strategic Research , RMA15-0030
Available from: 2018-10-16 Created: 2018-10-16 Last updated: 2018-11-02Bibliographically approved
Donzel-Gargand, O., Thersleff, T., Keller, J., Törndahl, T., Larsson, F., Wallin, E., . . . Edoff, M. (2018). Deep surface Cu depletion induced by K in high-efficiency Cu(In,Ga)Se2 solar cell absorbers. Progress in Photovoltaics, 26(9), 730-739
Open this publication in new window or tab >>Deep surface Cu depletion induced by K in high-efficiency Cu(In,Ga)Se2 solar cell absorbers
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2018 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 26, no 9, p. 730-739Article in journal (Refereed) Published
Abstract [en]

In this work, we used K‐rich glass substrates to provide potassium during the coevaporation of Cu(In,Ga)Se2 (CIGS) absorber layers. Subsequently, we applied a postdeposition treatment (PDT) using KF or RbF to some of the grown absorbers. It was found that the presence of K during the growth of the CIGS layer led to cell effi- ciencies beyond 17%, and the addition of a PDT pushed it beyond 18%. The major finding of this work is the observation of discontinuous 100‐ to 200‐nm‐deep Cu‐ depleted patches in the vicinity of the CdS buffer layer, correlated with the presence of K during the growth of the absorber layer. The PDT had no influence on the forma- tion of these patches. A second finding concerns the composition of the Cu‐depleted areas, where an anticorrelation between Cu and both In and K was measured using scanning transmission electron microscopy. Furthermore, a steeper Ga/(In+Ga) ratio gradient was measured for the absorbers grown with the presence of K, suggesting that K hinders the group III element interdiffusion. Finally, no Cd in‐diffusion to the CIGS layer could be detected. This indicates that if CdCu substitution occurs, either their concentration is below our instrumental detection limit or its presence is contained within the first 6 nm from the CdS/CIGS interface.

Keywords
CIGS, Cu depletion, EELS, OVC, Raman, solar cell, TEM
National Category
Other Materials Engineering Energy Systems
Identifiers
urn:nbn:se:uu:diva-357120 (URN)10.1002/pip.3010 (DOI)000442501000004 ()
Funder
Swedish Research CouncilSwedish Energy AgencyEU, Horizon 2020, 720887
Available from: 2018-08-12 Created: 2018-08-12 Last updated: 2018-11-13Bibliographically approved
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
Alberto, H. V., Vilao, R. C., Vieira, R. B., Gil, J. M., Weidinger, A., Sousa, M. G., . . . Salman, Z. (2018). Slow-muon study of quaternary solar-cell materials: Single layers and p-n junctions. PHYSICAL REVIEW MATERIALS, 2(2), Article ID 025402.
Open this publication in new window or tab >>Slow-muon study of quaternary solar-cell materials: Single layers and p-n junctions
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2018 (English)In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 2, no 2, article id 025402Article in journal (Refereed) Published
Abstract [en]

Thin films and p-n junctions for solar cells based on the absorber materials Cu(In, Ga) Se-2 and Cu2ZnSnS4 were investigated as a function of depth using implanted low energy muons. The most significant result is a clear decrease of the formation probability of the Mu(+) state at the heterojunction interface as well as at the surface of the Cu(In, Ga)Se-2 film. This reduction is attributed to a reduced bonding reaction of the muon in the absorber defect layer at its surface. In addition, the activation energies for the conversion from a muon in an atomiclike configuration to a anion-bound position are determined from temperature-dependence measurements. It is concluded that the muon probe provides a measurement of the effective surface defect layer width, both at the heterojunctions and at the films. The CIGS surface defect layer is crucial for solar-cell electrical performance and additional information can be used for further optimizations of the surface.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-346665 (URN)10.1103/PhysRevMaterials.2.025402 (DOI)000424511700004 ()
Available from: 2018-03-20 Created: 2018-03-20 Last updated: 2018-03-20Bibliographically approved
Keller, J., Shariati, M.-N., Aijaz, A., Riekehr, L., Kubart, T., Edoff, M. & Törndahl, T. (2018). Using hydrogen‐doped In2O3 films as a transparent back contact in (Ag,Cu)(In,Ga)Se2 solar cells. Progress in Photovoltaics, 26(3), 159-170
Open this publication in new window or tab >>Using hydrogen‐doped In2O3 films as a transparent back contact in (Ag,Cu)(In,Ga)Se2 solar cells
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2018 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 26, no 3, p. 159-170Article in journal (Refereed) Published
Abstract [en]

This study evaluates the potential of hydrogen‐doped In2O3 (IOH) as a transparent back contact material in (Agy,Cu1‐y)(In1‐x,Gax)Se2 solar cells. It is found that the presence of Na promotes the creation of Ga2O3 at the back contact during (Agy,Cu1‐y)(In1‐x,Gax)Se2 growth. An excessive Ga2O3 formation results in a Ga depletion, which extends deep into the absorber layer. Consequently, the beneficial back surface field is removed and a detrimental reversed electrical field establishes. However, for more moderate Ga2O3 amounts (obtained with reduced Na supply), the back surface field can be preserved. Characterization of corresponding solar cells suggests the presence of an ohmic back contact, even at absorber deposition temperatures of 550°C. The best solar cell with an IOH back contact shows a fill factor of 74% and an efficiency (η) of 16.1% (without antireflection coating). The results indicate that Ga2O3 does not necessarily act as a transport barrier in the investigated system. Observed losses in open circuit voltage (VOC) as compared to reference samples with a Mo back contact are ascribed to a lower Na concentration in the absorber layer.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-363286 (URN)10.1002/pip.2977 (DOI)
Funder
Swedish Energy Agency, 2016-008376
Available from: 2018-10-16 Created: 2018-10-16 Last updated: 2018-10-18
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
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