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Platzer Björkman, Charlotte
Alternative names
Publications (10 of 101) Show all publications
Larsen, J. K., Keller, J., Lundberg, O., Jarmar, T., Riekehr, L., Scragg, J. J. & Platzer Björkman, C. (2018). Sulfurization of Co-Evaporated Cu(In,Ga)Se-2 as a Postdeposition Treatment. IEEE Journal of Photovoltaics, 8(2), 604-610
Open this publication in new window or tab >>Sulfurization of Co-Evaporated Cu(In,Ga)Se-2 as a Postdeposition Treatment
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2018 (English)In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 8, no 2, p. 604-610Article in journal (Refereed) Published
Abstract [en]

It is investigated if the performance of Cu(In,Ga)Se-2 (CIGSe) solar cells produced by co-evaporation can be improved by surface sulfurization in a postdeposition treatment. The expected benefit would be the formation of a sulfur/selenium gradient resulting in reduced interface recombination and increased open-circuit voltage. In the conditions used here it was, however, found that the reaction of the CIGSe layer in a sulfur environment results in the formation of a CuInS2 (CIS) surface phase containing no or very little selenium and gallium. At the same time, a significant pile up of gallium was observed at the CIGSe/CIS boundary. This surface structure was formed for a wide range of annealing conditions investigated in this paper. Increasing the temperature or extending the time of the dwell stage had a similar effect on the material. The gallium enrichment and CIS surface layer widens the surface bandgap and therefore increases the open-circuit voltage. At the same time, the fill factor is reduced, since the interface layer acts as an electron barrier. Due to the balance of these effects, the conversion efficiency could not be improved.

Place, publisher, year, edition, pages
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2018
Keywords
Alloying, Cu(In, Ga)Se-2 (CIGSe), postdeposition treatment, surface treatment, thin-film solar cells
National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-348836 (URN)10.1109/JPHOTOV.2018.2793759 (DOI)000425525100034 ()
Funder
Swedish Foundation for Strategic Research , RMA15-0030
Available from: 2018-04-23 Created: 2018-04-23 Last updated: 2018-05-02Bibliographically approved
Rudisch, K., Davydova, A., Platzer Björkman, C. & Scragg, J. J. (2018). The effect of stoichiometry on Cu-Zn ordering kinetics in Cu2ZnSnS4 thin film. Paper presented at 29th International Conference on Defects in Semiconductors (ICDS), JUL 31-AUG 04, 2017, Matsue, JAPAN. Journal of Applied Physics, 123(16), Article ID 161558.
Open this publication in new window or tab >>The effect of stoichiometry on Cu-Zn ordering kinetics in Cu2ZnSnS4 thin film
2018 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 123, no 16, article id 161558Article in journal (Refereed) Published
Abstract [en]

Cu-Zn disorder in Cu2ZnSnS4 (CZTS) may be responsible for the large open circuit voltage deficit in CZTS based solar cells. In this study, it was investigated how composition-dependent defect complexes influence the order-disorder transition. A combinatorial CZTS thin film sample was produced with a cation composition gradient across the sample area. The graded sample was exposed to various temperature treatments and the degree of order was analyzed with resonant Raman spectroscopy for various compositions ranging from E- and A-type to B-, F-, and C-type CZTS. We observe that the composition has no influence on the critical temperature of the order-disorder transition, but strongly affects the activation energy. Reduced activation energy is achieved with compositions with Cu/Sn > 2 or Cu/Sn < 1.8 suggesting an acceleration of the cation ordering in the presence of vacancies or interstitials. This is rationalized with reference to the effect of point defects on exchange mechanisms. The implications for reducing disorder in CZTS thin films are discussed in light of the new findings.

National Category
Materials Chemistry Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-356091 (URN)10.1063/1.5010081 (DOI)000431147200088 ()
Conference
29th International Conference on Defects in Semiconductors (ICDS), JUL 31-AUG 04, 2017, Matsue, JAPAN
Funder
Swedish Energy AgencySwedish Research CouncilStandUpKnut and Alice Wallenberg Foundation
Available from: 2018-07-13 Created: 2018-07-13 Last updated: 2018-07-13Bibliographically 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
Kosyak, V., Postnikov, A. V., Scragg, J. J., Scarpulla, M. A. & Platzer Björkman, C. (2017). Calculation of point defect concentration in Cu2ZnSnS4: Insights into the high-temperature equilibrium and quenching. Journal of Applied Physics, 122(3), Article ID 035707.
Open this publication in new window or tab >>Calculation of point defect concentration in Cu2ZnSnS4: Insights into the high-temperature equilibrium and quenching
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2017 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 122, no 3, article id 035707Article in journal (Refereed) Published
Abstract [en]

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

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2017
National Category
Physical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-332848 (URN)10.1063/1.4994689 (DOI)000406128800046 ()
Funder
Swedish Research Council
Available from: 2017-11-09 Created: 2017-11-09 Last updated: 2017-11-14Bibliographically approved
Englund, S., Paneta, V., Primetzhofer, D., Ren, Y., Donzel-Gargand, O., Larsen, J. K., . . . Platzer Björkman, C. (2017). Characterization of TiN back contact interlayers with varied thickness for Cu2ZnSn(S,Se)4 thin film solar cells. Thin Solid Films, 639, 91-97
Open this publication in new window or tab >>Characterization of TiN back contact interlayers with varied thickness for Cu2ZnSn(S,Se)4 thin film solar cells
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2017 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 639, p. 91-97Article in journal (Refereed) Published
Abstract [en]

TiN thin films have previously been used as intermediate barrier layers on Mo back contacts in CZTS(e) solar cells to suppress excessive reaction of the Mo in the annealing step. In this work, TiN films with various thickness (20, 50 and 200 nm) were prepared with reactive DC magnetron sputtering on Mo/SLG substrates and annealed, without CZTS(e) layers, in either S or Se atmospheres. The as-deposited references and the annealed samples were characterized with X-ray Photoelectron Spectroscopy, X-ray Diffraction, Time-of-Flight-Elastic Recoil Detection Analysis, Time-of-Flight-Medium-Energy Ion Scattering, Scanning Electron Microscopy and Scanning Transmission Electron Microscopy – Electron Energy Loss Spectroscopy. It was found that the as-deposited TiN layers below 50 nm show discontinuities, which could be related to the surface roughness of the Mo. Upon annealing, TiN layers dramatically reduced the formation of MoS(e)2, but did not prevent the sulfurization or selenization of Mo. The MoS(e)2 had formed near the discontinuities, both below and above the TiN layers. Another unexpected finding was that the thicker TiN layer increased the amount of Na diffused to the surface after anneal, and we suggest that this effect is related to the Na affinity of the TiN layers and the MoS(e)2 thickness.

Keywords
Molybdenum, Titanium nitride, Interlayer, Back contact, Sulfurization, Selenization, CZTS, Thin film solar cell
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-335799 (URN)10.1016/j.tsf.2017.08.030 (DOI)000412787200014 ()
Funder
Swedish Foundation for Strategic Research , FFL12-0178
Available from: 2017-12-08 Created: 2017-12-08 Last updated: 2018-01-10Bibliographically approved
Ren, Y., Ross, N., Larsen, J. K., Rudisch, K., Scragg, J. J. & Platzer-Björkman, C. (2017). Evolution of Cu2ZnSnS4 during Non-Equilibrium Annealing with Quasi-in Situ Monitoring of Sulfur Partial Pressure. Chemistry of Materials, 29(8), 3713-3722
Open this publication in new window or tab >>Evolution of Cu2ZnSnS4 during Non-Equilibrium Annealing with Quasi-in Situ Monitoring of Sulfur Partial Pressure
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2017 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 29, no 8, p. 3713-3722Article in journal (Refereed) Published
Abstract [en]

Chalcogen-based materials like Cu2ZnSnS4 (CZTS) have attracted extensive attention for applications such as photovoltaics and water splitting. However, an inability to monitor the sulfur partial pressure (P-S2) during the non equilibrium annealing process at high temperatures complicates the synthesis of CZTS with controlled optoelectronic properties. Here we demonstrate that P-S2 can be monitored by investigating the Sn-S phase transformation. We showed that P-S2 drops considerably over the annealing time, causing gradual alterations in CZTS: (i) a change in defect type and (ii) evolution of ZnS and SnxSy phases. With additional ordering treatment, we observed that the low room-temperature photoluminescence energy usually seen in CZTS can result from insufficient P-S2 during annealing. It is proven that remarkable V-oc beyond 700 mV for solar cells with nonoptimal CdS buffer can be repeatedly achieved when CZTS is prepared under a sufficiently high P-S2. An ordering treatment before CdS deposition can further improve V-oc to 783 mV.

National Category
Materials Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-323462 (URN)10.1021/acs.chemmater.7b00671 (DOI)000400233100042 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research Swedish Research Council
Available from: 2017-06-07 Created: 2017-06-07 Last updated: 2017-06-09Bibliographically approved
Bras, P., Frisk, C., Tempez, A., Niemi, E. & Platzer Björkman, C. (2017). Ga-grading and Solar Cell Capacitance Simulation of an industrial Cu(In,Ga)Se2 solar cell produced by an in-line vacuum, all-sputtering process. Thin Solid Films, 636, 367-374
Open this publication in new window or tab >>Ga-grading and Solar Cell Capacitance Simulation of an industrial Cu(In,Ga)Se2 solar cell produced by an in-line vacuum, all-sputtering process
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2017 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 636, p. 367-374Article in journal (Refereed) Published
Abstract [en]

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

Keywords
Copper indium gallium selenide, In-line vacuum, Sputtering, Cadmium-free, SCAPS, Gallium-grading
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-329771 (URN)10.1016/j.tsf.2017.06.031 (DOI)000408037800053 ()
Available from: 2017-09-21 Created: 2017-09-21 Last updated: 2017-11-20Bibliographically approved
Ren, Y., Richter, M., Keller, J., Redinger, A., Unold, T., Donzel-Gargand, O., . . . Platzer Björkman, C. (2017). Investigation of the SnS/Cu2ZnSnS4 interfaces in Kesterite Thin-Film Solar Cells. ACS Energy Letters, 2(5), 976-981
Open this publication in new window or tab >>Investigation of the SnS/Cu2ZnSnS4 interfaces in Kesterite Thin-Film Solar Cells
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2017 (English)In: ACS Energy Letters, E-ISSN 2380-8195, Vol. 2, no 5, p. 976-981Article in journal (Refereed) Published
Abstract [en]

Kesterite Cu2ZnSnS4 (CZTS), having only earth abundant elements, is a promising solar cell material. Nevertheless, the impact of the SnS secondary phase, which often forms alongside CZTS synthesis at high annealing temperature, on CZTS solar cells is poorly studied. We confirm, by means of X-ray diffraction, Raman scattering, and energy dispersive X-ray spectroscopy mapping, that this phase tends to segregate at both the surface and the back side of annealed CZTS films with Cu-poor and Zn-rich composition. Using electron beam-induced current measurements, it is further demonstrated that the formation of SnS on the CZTS surface is harmful for solar cells, whereas the SnS phase can be beneficial for solar cells when it segregates on the CZTS rear. This positive contribution of SnS could stem from a passivation effect at the CZTS/SnS rear interface. This work opens new possibilities for an alternative interface development for kesterite-based photovoltaic technology.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-314941 (URN)10.1021/acsenergylett.7b00151 (DOI)000401500200005 ()
Funder
EU, FP7, Seventh Framework Programme, 316488Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research Swedish Research Council
Available from: 2017-02-07 Created: 2017-02-07 Last updated: 2017-06-30Bibliographically approved
Platzer Björkman, C. (2017). Kesterite compound semiconductors for thin film solar cells. CURRENT OPINION IN GREEN AND SUSTAINABLE CHEMISTRY, 4, 84-90
Open this publication in new window or tab >>Kesterite compound semiconductors for thin film solar cells
2017 (English)In: CURRENT OPINION IN GREEN AND SUSTAINABLE CHEMISTRY, ISSN 2452-2236, Vol. 4, p. 84-90Article in journal (Refereed) Published
Abstract [en]

Thin film solar cells based on Cu2ZnSn(S, Se)(4), "CZTS", are attractive by combining high light absorption and high abundance of constituent elements. The efficiency of CZTS solar cells developed rapidly during the last decades, but significant improvements are still needed to reach commercially viable levels. This review covers the most recent trends in CZTS research; (i) alloying with new elements, (ii) exchange of CdS buffer layer with alternative materials, (iii) back contact engineering and (iv) defect studies as a function of compositional variations and annealing. Better understanding of the material and device limitations is expected to emerge from this research. In the perspective of large scale use of CZTS modules, non-toxicity and earth-abundance cannot be compromised in the view of competition with commercially mature CdTe and CIGS technologies. Large band gap kesterite derivatives for stable top cells in tandem solar cells is an interesting and less explored field meriting more attention.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2017
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-335690 (URN)10.1016/j.cogsc.2017.02.010 (DOI)000410695600014 ()
Available from: 2017-12-19 Created: 2017-12-19 Last updated: 2017-12-19Bibliographically approved
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