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Stolt, Lars
Publications (10 of 88) Show all publications
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 Agency
Available from: 2018-08-12 Created: 2018-08-12 Last updated: 2018-10-03Bibliographically 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
Donzel-Gargand, O., Thersleff, T., Keller, J., Törndahl, T., Larsson, F., Wallin, E., . . . Edoff, M. (2017). Cu-depleted patches induced by presence of K during growth of CIGS absorbers. In: : . Paper presented at 34th European PV Solar Energy Conference and Exhibition (EUPVSEC) 2017.
Open this publication in new window or tab >>Cu-depleted patches induced by presence of K during growth of CIGS absorbers
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2017 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

The conversion efficiency of the CIGS thin film solar cells has rapidly increased since introduction of the heavier alkali-doping (K, Rb, Cs). While the exclusive introduction of Na in the CIGS films has led to efficiencies up to 20,4% 1, the latest K, Rb or Cs post deposition treatments (PDT) have increased the efficiency to 22,6% 2. The exact role of this heavy-alkali PDT is still under discussion but three explanations have been discussed in the literature. First, that the heavy alkali PDT facilitates CdCu substitution, that results in an enhanced absorber type inversion, moving the p-n junction further into the CIGS bulk 3. Second, that the main effect from heavy alkali PDT is due to the formation of a K-In-Se2 layer, that passivates defects at the CIGS surface, reducing interface recombination 4. And third, that the heavy alkali PDT induces a Cu depletion at the surface of the CIGS which, by increasing the local Fermi level, increases the band bending; thus creating a higher potential barrier for holes to recombine 5.

National Category
Energy Systems Other Materials Engineering
Identifiers
urn:nbn:se:uu:diva-335110 (URN)
Conference
34th European PV Solar Energy Conference and Exhibition (EUPVSEC) 2017
Available from: 2017-11-30 Created: 2017-11-30 Last updated: 2017-12-29Bibliographically approved
Edoff, M., Jarmar, T., Shariati Nilsson, N., Wallin, E., Hogstrom, D., Stolt, O., . . . Stolt, L. (2017). High Voc in (Cu,Ag)(In,Ga)Se2 Solar Cells. IEEE Journal of Photovoltaics, 7(6), 1789-1794
Open this publication in new window or tab >>High Voc in (Cu,Ag)(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 6, p. 1789-1794Article in journal (Refereed) Published
Abstract [en]

In this contribution, we show that silver substitution for copper in Cu(In,Ga)Se-2 (CIGS) to form (Ag,Cu)(In, Ga)Se-2 (ACIGS) leads to a reduction of the voltage loss expressed as E-g/q-V-oc. This, in turn, leads to higher device efficiencies as compared to similar CIGS devices without Ag. We report V-oc at 814 mV at a conversion efficiency of 21% for our best ACIGS device with 20% of the group I element consisting of silver. Comparing ACIGS and CIGS devices with the same Ga/(Ga+ In) ratio, the ACIGS devices exhibit about 0.05 eV higher bandgap. Alkali postdeposition treatment with KF leads to improvements in efficiency both for CIGS and ACIGS, but we find that the dose of KF needed for optimum device for ACIGS is 10-20% of the dose used for CIGS.

Keywords
ACIGS, (Ag, Cu)(Ga, In)Se-2, KF pdt, KF post deposition treatment, thin film solar cells
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-341656 (URN)10.1109/JPHOTOV.2017.2756058 (DOI)000413934100044 ()
Funder
Swedish Foundation for Strategic Research StandUp
Available from: 2018-02-16 Created: 2018-02-16 Last updated: 2018-02-16Bibliographically approved
Abou-Ras, D., Wagner, S., Stanbery, B. J., Schock, H.-W., Scheer, R., Stolt, L., . . . Tiwari, A. N. (2017). Innovation highway: Breakthrough milestones and key developments in chalcopyrite photovoltaics from a retrospective viewpoint. 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, 2-12
Open this publication in new window or tab >>Innovation highway: Breakthrough milestones and key developments in chalcopyrite photovoltaics from a retrospective viewpoint
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2017 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 633, p. 2-12Article in journal (Refereed) Published
Abstract [en]

The present contribution is a summary of an event that was organized as a special evening session in Symposium V "Chalcogenide Thin-Film Solar Cells" at the E-MRS 2016 Spring Meeting, Lille, France. The presentations in this session were given by the coauthors of this paper. These authors present retrospectives of key developments in the field of Cu(In,Ga)(S,Se)(2) solar cells as they themselves had witnessed in their laboratories or companies. Also, anecdotes are brought up, which captured interesting circumstances in that evolutionary phase of the field. Because the focus was on historical perspectives rather than a comprehensive review of the field, recent developments intentionally were not addressed.

Keywords
Cu(ln, Ga)(5, Se)(2) solar cells, Retrospective, Cu2S solar cells, Point defects, Na impurity, Chemical bath deposition of buffer layers, Production processes for Cu(ln, Ga)(S, Se)(2)
National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-330017 (URN)10.1016/j.tsf.2017.01.005 (DOI)000404802300002 ()
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: 2017-09-25 Created: 2017-09-25 Last updated: 2017-09-27Bibliographically approved
Keller, J., Gustavsson, F., Stolt, L., Edoff, M. & Törndahl, T. (2017). On the beneficial effect of Al2O3 front contact passivation in Cu(In,Ga)Se2 solar cells. Solar Energy Materials and Solar Cells, 159, 189-196
Open this publication in new window or tab >>On the beneficial effect of Al2O3 front contact passivation in Cu(In,Ga)Se2 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. 189-196Article in journal (Refereed) Published
Abstract [en]

This study reports on the beneficial effect of an absorber surface passivation by Al2O3 on the performance of Cu(In, Ga)Se-2 (CIGSe) solar cells. Here the Al2O3 layer is deposited by atomic layer deposition (ALD) subsequently to a CdS buffer layer. It is shown that a very thin film of about 1 nm efficiently reduces the interface recombination rate if the buffer layer is too thin to not fully cover the CIGSe absorber. An Al2O3 thickness of 1 nm is sufficiently low to allow current transport via tunneling. Increasing the thickness to > 1 nm leads to a detrimental blocking behavior due to an exponentially decreasing tunnel current. Losses in open circuit voltage (V-oc) and fill factor (FF) when reducing the buffer layer thickness are significantly mitigated by implementing an optimized Al2O3 layer. It is further shown, that the heat treatment during the ALD step results in an increase in short circuit current density (J(sc)) of about 2 mA/cm(2). This observation is attributed to a widening of the space charge region in the CIGSe layer that in turn improves the collection probability of electrons. For not fully covering CdS layers the decrease in interface defect density by the passivation contributes as well, leading to a gain of about 5 mA/cm2 for cells without a buffer. Finally, the leakage current of the solar cell devices could be reduced when applying the Al2O3 layer on insufficiently covering CdS films, which proves the capability of mitigating the effect of shunts or bad diodes.

Keywords
CIGSe, Al2O3, Surface passivation, Atomic layer deposition, ALD
National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-306879 (URN)10.1016/j.solmat.2016.09.019 (DOI)000388053600022 ()
Funder
Swedish Energy Agency, 2012-004591VINNOVA, 2013-02199
Available from: 2016-11-03 Created: 2016-11-03 Last updated: 2017-11-29Bibliographically approved
Keller, J., Stolt, L., Edoff, M. & Törndahl, T. (2016). Atomic layer deposition of In2O3 transparent conductive oxide layers for application in Cu(In,Ga)Se2 solar cells with different buffer layers. Physica Status Solidi (a) applications and materials science, 213(6), 1541-1552
Open this publication in new window or tab >>Atomic layer deposition of In2O3 transparent conductive oxide layers for application in Cu(In,Ga)Se2 solar cells with different buffer layers
2016 (English)In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 213, no 6, p. 1541-1552Article in journal (Refereed) Published
Abstract [en]

This contribution presents the development of atomic layer deposited (ALD) In2O3 films for utilization as transparent conductive oxide (TCO) layers in Cu(In,Ga)Se2 (CIGSe) solar cells. The effects of ALD process parameters on the morphology and growth of In2O3 are studied and related to the electrical and optical properties of the films. Maintaining similar resistivity values compared to commonly used ZnO:Al (AZO) TCOs (ρ = (5–7) × 10−4 Ωcm), a superior mobility of μ ≈ 110 cm2/Vs could be achieved (more than five times higher than a ZnO:Al reference), which results in a significantly reduced parasitic optical absorption in the infrared region. Application of the optimized In2O3 layers in CIGSe solar cells with varying buffer layers (CdS and Zn1–xSnxOy (ZTO)) leads to a distinct improvement in short circuit current density Jsc in both cases. While for solar cells containing the ZTO/In2O3 window structure, a drop in open-circuit voltage Voc and a deterioration under illumination is observed, the TCO exchange (from AZO to In2O3) on CdS buffer layers results in an increase in Voc without detectable light bias degradation. The efficiency η of the best corresponding solar cells could be improved by about 1% absolute.

National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-275262 (URN)10.1002/pssa.201532883 (DOI)000378398900023 ()
Funder
Swedish Energy AgencyVINNOVA
Available from: 2016-02-02 Created: 2016-02-02 Last updated: 2017-11-30Bibliographically approved
Keller, J., Lindahl, J., Edoff, M., Stolt, L. & Törndahl, T. (2016). Potential gain in photocurrent generation for Cu(In,Ga)Se2 solar cells by using In2O3 as a transparent conductive oxide layer. Progress in Photovoltaics, 24(1), 102-107
Open this publication in new window or tab >>Potential gain in photocurrent generation for Cu(In,Ga)Se2 solar cells by using In2O3 as a transparent conductive oxide layer
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2016 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 24, no 1, p. 102-107Article in journal (Refereed) Published
Abstract [en]

This study highlights the potential of atomic layer deposited In2O3 as a highly transparent and conductive oxide (TCO)layer in Cu(In,Ga)Se2 (CIGSe) solar cells. It is shown that the efficiency of solar cells which use Zn-Sn-O (ZTO) as an alternativebuffer layer can be increased by employing In2O3 as a TCO because of a reduction of the parasitic absorption inthe window layer structure, resulting in 1.7 mA/cm2 gain in short circuit current density (Jsc). In contrast, a degradation ofdevice properties is observed if the In2O3 TCO is combined with the conventional CdS buffer layer. The estimated improvementfor large-scale modules is discussed.

Keywords
In2O3; ALD; Zn-Sn-O; alternative window layer; CIGSe; TCO
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-260877 (URN)10.1002/pip.2655 (DOI)000370320100011 ()
Funder
Swedish Energy AgencyVINNOVA
Available from: 2015-08-25 Created: 2015-08-25 Last updated: 2017-12-04Bibliographically approved
Westin, P.-O., Zimmermann, U., Stolt, L. & Edoff, M. (2009). Reverse bias damage in CIGS modules. In: 24th European Photovoltaic Solar Energy Conference and Exhibition: Conference 21-25 September 2009 - Exhibition 21-24 September 2009, 2009 Hamburg proceedings. Paper presented at 24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany (pp. 2967-2970). München: WIP-Renewable Energies
Open this publication in new window or tab >>Reverse bias damage in CIGS modules
2009 (English)In: 24th European Photovoltaic Solar Energy Conference and Exhibition: Conference 21-25 September 2009 - Exhibition 21-24 September 2009, 2009 Hamburg proceedings, München: WIP-Renewable Energies , 2009, p. 2967-2970Conference paper, Published paper (Refereed)
Abstract [en]

When solar modules are partially shaded they will be under conditions of partial reverse bias. To test and evaluate the effect of reverse bias, CIGS thin film PV modules were placed under extreme conditions of reverse stress.  Stressing  caused  modules  to  exhibit  visible  “wormlike”  damages.  These  damages  were  caused  by  hot  spot activity during reverse stress. Local heating resulted in pore formation and forced the hot spot to move within the cell. This effect appeared to cause intermixing of the top ZnO layer with the CIGS absorber. Some phase segregation of an undetermined, Cu rich compound was also found near the back contact. Electrically, the observed damages caused local shunt conductance to increase resulting in irreversibly reduced module fill factors.

Place, publisher, year, edition, pages
München: WIP-Renewable Energies, 2009
Keywords
Cu(InGa)Se2, Modules, Stability
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electronics
Identifiers
urn:nbn:se:uu:diva-109181 (URN)10.4229/24thEUPVSEC2009-3BV.5.34 (DOI)3-936338-25-6 (ISBN)
Conference
24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany
Available from: 2009-10-13 Created: 2009-10-09 Last updated: 2016-04-14Bibliographically approved
Powalla, M., Kessler, F., Hariskos, D., Voorwinden, G., Tiwari, A. N., Brémaud, D., . . . Auvray, S. (2007). Highly productive manufacturing of CIS-based large-area modules. In: : . Paper presented at Proceedings of the 22nd European Photovoltaic Solar Energy Conference, Milano, 2007 : 3DO.9.2.
Open this publication in new window or tab >>Highly productive manufacturing of CIS-based large-area modules
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2007 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-12897 (URN)
Conference
Proceedings of the 22nd European Photovoltaic Solar Energy Conference, Milano, 2007 : 3DO.9.2
Available from: 2008-01-18 Created: 2008-01-18 Last updated: 2016-04-07Bibliographically approved
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