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Larsen, J. K., Larsson, F., Törndahl, T., Saini, N., Riekehr, L., Ren, Y., . . . Platzer Björkman, C. (2019). Cadmium Free Cu2ZnSnS4 Solar Cells with 9.7% Efficiency. Advanced Energy Material, 9(21), Article ID 1900439.
Open this publication in new window or tab >>Cadmium Free Cu2ZnSnS4 Solar Cells with 9.7% Efficiency
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2019 (English)In: Advanced Energy Material, ISSN 1614-6832, Vol. 9, no 21, article id 1900439Article in journal (Refereed) Published
Abstract [en]

Cu2ZnSnS4(CZTS) thin-film solar cell absorbers with different bandgaps can be produced by parameter variation during thermal treatments. Here, the effects of varied annealing time in a sulfur atmosphere and an ordering treatment of the absorber are compared. Chemical changes in the surface due to ordering are examined, and a downshift of the valence band edge is observed. With the goal to obtain different band alignments, these CZTS absorbers are combined with Zn1−xSnxOy (ZTO) or CdS buffer layers to produce complete devices. A high open circuit voltage of 809 mV is obtained for an ordered CZTS absorber with CdS buffer layer, while a 9.7% device is obtained utilizing a Cd free ZTO buffer layer. The best performing devices are produced with a very rapid 1 min sulfurization, resulting in very small grains.

Keywords
Cu2ZnSnS4, thermal treatment, thin-film solar cells, valence bands
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-382533 (URN)10.1002/aenm.201900439 (DOI)000470925900010 ()
Funder
Swedish Energy Agency, 2017-004796Swedish Foundation for Strategic Research , RMA15-0030Swedish Foundation for Strategic Research , FFL12-0178
Available from: 2019-04-26 Created: 2019-04-26 Last updated: 2019-07-05Bibliographically approved
Aboulfadl, H., Keller, J., Larsen, J. K., Thuvander, M., Riekehr, L., Edoff, M. & Platzer Björkman, C. (2019). Microstructural Characterization of Sulfurization Effects in Cu(In,Ga)Se-2 Thin Film Solar Cells. Paper presented at Atom Probe Tomography and Microscopy (APT and M) Conference, JUN 10-15, 2018, Gaithersburg, MD. Microscopy and Microanalysis, 25(2), 532-538
Open this publication in new window or tab >>Microstructural Characterization of Sulfurization Effects in Cu(In,Ga)Se-2 Thin Film Solar Cells
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2019 (English)In: Microscopy and Microanalysis, ISSN 1431-9276, E-ISSN 1435-8115, Vol. 25, no 2, p. 532-538Article in journal (Refereed) Published
Abstract [en]

Surface sulfurization of Cu(In,Ga)Se-2 (CIGSe) absorbers is a commonly applied technique to improve the conversion efficiency of the corresponding solar cells, via increasing the bandgap towards the heterojunction. However, the resulting device performance is understood to be highly dependent on the thermodynamic stability of the chalcogenide structure at the upper region of the absorber. The present investigation provides a high-resolution chemical analysis, using energy dispersive X-ray spectrometry and laser-pulsed atom probe tomography, to determine the sulfur incorporation and chemical re-distribution in the absorber material. The post-sulfurization treatment was performed by exposing the CIGSe surface to elemental sulfur vapor for 20 min at 500 degrees C. Two distinct sulfur-rich phases were found at the surface of the absorber exhibiting a layered structure showing In-rich and Ga-rich zones, respectively. Furthermore, sulfur atoms were found to segregate at the absorber grain boundaries showing concentrations up to similar to 7 at% with traces of diffusion outwards into the grain interior.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS, 2019
Keywords
atom probe, Cu(In, Ga)Se-2, solar cells, surface treatment, thin films
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-385571 (URN)10.1017/S1431927619000151 (DOI)000466756600030 ()30853031 (PubMedID)
Conference
Atom Probe Tomography and Microscopy (APT and M) Conference, JUN 10-15, 2018, Gaithersburg, MD
Funder
Swedish Foundation for Strategic Research , RMA15-0030
Available from: 2019-06-17 Created: 2019-06-17 Last updated: 2019-06-17Bibliographically approved
Suvanam, S. S., Larsen, J. K., Ross, N., Kosyak, V., Hallen, A. & Platzer Björkman, C. (2018). Extreme radiation hard thin film CZTSSe solar cell. Solar Energy Materials and Solar Cells, 185, 16-20
Open this publication in new window or tab >>Extreme radiation hard thin film CZTSSe solar cell
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2018 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 185, p. 16-20Article in journal (Refereed) Published
Abstract [en]

In this work, we have demonstrated the extreme radiation hardness of thin film CZTSSe solar cells. Thin film solar cells with CZTSSe, CZTS and CIGS absorber layers were irradiated with 3 MeV protons. No degradation in device parameters was observed until a displacement damage dose of 2 x 10(10) MeV/g for CZTS and CZTSSe. CIGS solar cells degraded by 13% at the same dose. For the highest proton dose both the CZTSSe and CZTS degraded by 16% while CIGS suffered from 34% degradation in efficiency. The degradation in efficiency maybe attributed to the reduction in the minority carrier lifetime due to radiation induced lattice defects. Comparisons with previously available literature show that our CZTS technology has superior radiation hardness by about two orders of magnitude compared to existing state of the art Si and GaAs technology.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2018
Keywords
CZTSSe, Proton radiation, Space solar cells, Radiation hardness
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:uu:diva-361023 (URN)10.1016/j.solmat.2018.05.012 (DOI)000437816100003 ()
Available from: 2018-09-20 Created: 2018-09-20 Last updated: 2018-09-20Bibliographically approved
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: 2018-09-14Bibliographically 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
Igalson, M., Macielak, K., Urbaniak, A., Barreau, N. & Larsen, J. K. (2017). Excitation spectra of defect levels derived from photoinduced current transient spectroscopy - a tool for studying deep levels in Cu(In,Ga)Se2 compounds. Paper presented at Symposium V on Thin Film Chalcogenide Photovoltaic Materials held at the 13th E-MRS Spring Meeting, MAY 02-06, 2016, Lille, FRANCE. Thin Solid Films, 633(SI), 227-230
Open this publication in new window or tab >>Excitation spectra of defect levels derived from photoinduced current transient spectroscopy - a tool for studying deep levels in Cu(In,Ga)Se2 compounds
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2017 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 633, no SI, p. 227-230Article in journal (Refereed) Published
Abstract [en]

Energy required for the optical excitation of carriers onto defect levels is a parameter that compliments thermal activation energy and helps to understand the electronic properties of defects under study. Here a modification of the photoinduced current transient spectroscopy (PICTS) based on phase-sensitive detection is proposed which makes possible to measure the excitation spectra of defect levels. The representative results of the excitation spectra of the epitaxial CuGaSe2 and polycrystalline Cu(In,Ga)Se2 thin films are presented. They illustrate the usefulness of the method as a tool for studying defect properties by providing data that supplement information derived from standard PICTS spectroscopy.

Keywords
Defect levels, Copper indium gallium selenide, Photocurrent, Photoinduced current transient spectroscopy
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-330019 (URN)10.1016/j.tsf.2016.11.046 (DOI)000404802300043 ()
Conference
Symposium V on Thin Film Chalcogenide Photovoltaic Materials held at the 13th E-MRS Spring Meeting, MAY 02-06, 2016, Lille, FRANCE
Available from: 2017-10-13 Created: 2017-10-13 Last updated: 2017-10-13Bibliographically approved
Li, S.-Y., Zamulko, S., Persson, C., Ross, N., Larsen, J. K. & Platzer-Björkman, C. (2017). Optical properties of Cu2ZnSn(SxSe1-x)(4) solar absorbers: Spectroscopic ellipsometry and ab initio calculations. Applied Physics Letters, 110(2), Article ID 021905.
Open this publication in new window or tab >>Optical properties of Cu2ZnSn(SxSe1-x)(4) solar absorbers: Spectroscopic ellipsometry and ab initio calculations
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2017 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 110, no 2, article id 021905Article in journal (Refereed) Published
Abstract [en]

Dielectric functions of Cu2ZnSn(SxSe1-x)(4) thin film absorbers with varied x were determined by spectroscopic ellipsometry and ab initio calculations. From the combination of experimental and theoretical studies, the fundamental interband transition energy E-0 (similar to 1-1.5 eV) and the next following transition energy E-1 (similar to 2-3 eV) were identified and found to blue-shift with increasing sulfur anion content, while keeping the energy separation E-1 - E-0 almost constant, similar to 1.4 eV from experiments, and 1 eV from theory. In addition, the average dielectric responses were found to decrease with sulfur anion content from both theoretical and experimental results. The Tauc optical bandgap value E-g determined on samples prepared on Mo and soda lime glass substrate showed a positive linear relationship between x and bandgap E-g. The bandgap bowing factor determined from the theoretical data is 0.09 eV. (C) 2017 Author(s).

National Category
Physical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-316037 (URN)10.1063/1.4973353 (DOI)000392835300025 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilSwedish Foundation for Strategic Research
Available from: 2017-02-24 Created: 2017-02-24 Last updated: 2017-11-29Bibliographically approved
Ross, N., Larsen, J., Grini, S., Vines, L. & Platzer-Björkman, C. (2017). Practical limitations to selenium annealing of compound co-sputtered Cu2ZnSnS4 as a route to achieving sulfur-selenium graded solar cell absorbers. Thin Solid Films, 623, 110-115
Open this publication in new window or tab >>Practical limitations to selenium annealing of compound co-sputtered Cu2ZnSnS4 as a route to achieving sulfur-selenium graded solar cell absorbers
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2017 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 623, p. 110-115Article in journal (Refereed) Published
Abstract [en]

The suitability of selenium annealing as a technique to introduce energy band gap gradients via sulfur selenium substitution in Cu2ZnSnS4 (CZTS) films is evaluated. Compound co-sputtered CZTS precursors are annealed in selenium atmosphere at 425 degrees C, either as-deposited or after a short time sulfur pre-anneal. The films are investigated by Raman spectroscopy and X-ray diffractometry, and the spatial distribution of elemental species measured by secondary ion mass spectrometry and energy dispersive X-ray spectroscopy. Sulfur-selenium gradients are not achieved for the as-deposited precursor. Sulfur-selenium gradients are achieved in the early stages of annealing for pre-anneal samples, where Cu2ZnSn(S,Se)(4) (CZTSSe) formation is found to be correlated spatially with sodium distribution. These gradients are lost as the annealing progresses. Selenisation occurs by CZTSSe grain growth, rather than by direct substitution of selenium for sulfur. The spatial correlation of high sodium concentration with CZTSSe formation suggests that liquid phase sodium selenide facilitates selenium incorporation during recrystallisation, limiting the practicality of anion-grading of CZTSSe during the annealing step as a means of establishing a graded band gap.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2017
Keywords
CZTSSe, Diffusion, Crystallisation, Sodium, Band gap gradient
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-320783 (URN)10.1016/j.tsf.2016.12.044 (DOI)000394191300016 ()
Funder
Swedish Foundation for Strategic Research
Available from: 2017-04-25 Created: 2017-04-25 Last updated: 2017-04-25Bibliographically approved
Larsen, J. K., Ren, Y., Ross, N., Särhammar, E., Li, S. & Platzer Björkman, C. (2017). Surface modification through air annealing Cu2ZnSn(S,Se)4 absorbers. Paper presented at Symposium V on Thin Film Chalcogenide Photovoltaic Materials held at the 13th E-MRS Spring Meeting, MAY 02-06, 2016, Lille, FRANCE. Thin Solid Films, 633, 118-121
Open this publication in new window or tab >>Surface modification through air annealing Cu2ZnSn(S,Se)4 absorbers
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2017 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 633, p. 118-121Article in journal (Refereed) Published
Abstract [en]

Recent studies demonstrate that air annealing can have a positive effect on the device performance of Cu2ZnSn(SxSe1-x)(4)[CZTSSe] solar cells. In this work air annealing of the selenium containing CZTSSe is compared to the pure sulfide CZTS. It is discovered that the selenium containing absorbers benefit from air annealing at higher temperatures than selenium free absorbers. The highest efficiency obtained utilizing the air annealing treatment on selenium containing absorbers is 9.7%. We find that the band gap is narrowed when air annealing, which is partially explained by increased Cu-Zn disorder. Furthermore Zn enrichment of the surface after etching is identified as a possible cause of enhanced device performance. It is additionally observed that elemental selenium present on the CZTSSe surface is reduced in the air annealing treatment. Selenium removal is another possible explanation for the enhanced performance caused by the air annealing treatment.

Keywords
CZTS, Kesterite, Thin film solar cells, Surface modification, Passivation
National Category
Materials Engineering Physical Sciences
Identifiers
urn:nbn:se:uu:diva-330018 (URN)10.1016/j.tsf.2016.08.030 (DOI)000404802300023 ()
Conference
Symposium V on Thin Film Chalcogenide Photovoltaic Materials held at the 13th E-MRS Spring Meeting, MAY 02-06, 2016, Lille, FRANCE
Note

Surface modification through air annealing Cu2ZnSn(S,Se)(4) absorbers

Available from: 2017-10-11 Created: 2017-10-11 Last updated: 2018-09-14Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-7392-4701

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