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The Effect of Absorber Stoichiometry on the Stability of Widegap (Ag,Cu)(In,Ga)Se2 Solar Cells
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solar Cell Technology.ORCID iD: 0000-0001-9972-4655
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solar Cell Technology.ORCID iD: 0000-0002-3461-6036
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solar Cell Technology.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solar Cell Technology.ORCID iD: 0000-0003-4111-4613
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2022 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 259, no 11, article id 2200104Article in journal (Refereed) Published
Abstract [en]

(Ag,Cu)(In,Ga)Se2 solar cells with bandgaps of ≈1.45 eV with a large spread in absorber stoichiometry are characterized with the intention of assessing the effect of composition on the stability of the devices. This material is observed to have a poor diffusion length, leading to very strong dependence upon the depletion region width for charge carrier collection. The depletion width is observed to depend strongly upon the stoichiometry value and shrinks significantly after an initial period of dark storage. It is also seen that the depletion width can be varied strongly through light-soaking and dry-heat treatments, with prolonged annealing leading to detrimental contraction and light soaking leading to expansion which increases current collection. The extent of depletion width variation in response to the treatments is also clearly linked to absorber stoichiometry. Consequently, the device performance, particularly the current output, exhibits a stoichiometry dependence and is considerably affected after each round of treatment. Possible causes of this behavior are discussed.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2022. Vol. 259, no 11, article id 2200104
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:uu:diva-496436DOI: 10.1002/pssb.202200104ISI: 000847103800001OAI: oai:DiVA.org:uu-496436DiVA, id: diva2:1736444
Funder
Swedish Energy Agency, 48479−1Swedish Research Council, 2019−04793Available from: 2023-02-13 Created: 2023-02-13 Last updated: 2024-12-04Bibliographically approved
In thesis
1. Electrical Characterisation of (Ag,Cu)(In,Ga)Se2 Thin Film Solar Cells To Investigate Stability
Open this publication in new window or tab >>Electrical Characterisation of (Ag,Cu)(In,Ga)Se2 Thin Film Solar Cells To Investigate Stability
2023 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This licentiate thesis gives a summary of electrical characterisation techniques, detailing their use to investigate and understand stability and meta-stability in thin-film solar cells, with a focus on the chalcopyrite material system. Experimental data is used to illustrate the information that can be extracted with these measurements, highlighting the deeper insights that can be drawn from complementary measurements. For example, short-circuit current losses in (Ag,Cu)(In,Ga)Se2 after prolonged storage and annealing are attributed to changes in the net doping, as are significant open-circuit voltage losses observed after lightsoaking. Characterisation is also shown to suggest that the amount of Ag in the alloy plays a significant role in its stability, with a similar significance indicated for Ga.

Place, publisher, year, edition, pages
Uppsala University, 2023
Keywords
Solar Cells, Stability, Electrical Characterisation
National Category
Other Engineering and Technologies not elsewhere specified
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-495240 (URN)
Presentation
2023-01-30, 13:15 (English)
Opponent
Supervisors
Available from: 2023-02-13 Created: 2023-01-25 Last updated: 2023-02-13Bibliographically approved
2. An Investigation of Meta-Stability in (Ag,Cu)(In,Ga)Se2 Solar Cells
Open this publication in new window or tab >>An Investigation of Meta-Stability in (Ag,Cu)(In,Ga)Se2 Solar Cells
2025 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis summarises a series of works investigating the effect of Ag alloying on the long-term stability and meta-stability of wide-gap (Ag,Cu)(In,Ga)Se2 (ACIGS) thin-film solar cells. External quantum efficiency, current-voltage, and capacitance-based measurements have been the main characterisation techniques used to investigate these behaviours. Although Ag alloying facilitates high efficiencies and open-circuit voltages (VOC) in the wide-gap devices (despite the high Ga contents), it is revealed that for a [Ag]/([Ag]+[Cu]) ratio (AAC) in excess of 0.5, the behaviour of ACIGS devices changes significantly. Above the threshold, a strong dependence of net doping concentration (Nnet) on group-I/group-III stoichiometry (I/III) is observed, which in turn dictates performance due to low diffusion lengths in high-Ga absorbers. Close-stoichiometric (I/III>0.92) absorbers are almost fully depleted (depletion widths up to 2μm), whilst off-stoichiometric (I/III<0.92) absorbers have high Nnet (1016-1017cm−3). Lightsoaking treatments induce significant reductions in Nnet (up to two orders of magnitude), whilst dark storage and annealing lead to increases. The corresponding changes in the depletion widths are large, leading to significant variations in device performance. Independent of Ag contents, high Ga contents lead to VOC losses after lightsoaking. These meta-stable effects lead to a poor long-term stability in the devices, with one month’s dark storage resulting in 1-2% efficiency losses (absolute) and the persistent VOC losses contributing a further 1-2% loss (absolute). Additionally, a combination of high Ga and high Ag contents is seen to cause large voltage hysteresis in the devices, which is a further concern for the long-term stability and reliability of modules. It is suggested that defects in ordered vacancy compounds, which segregate to the front surface of the high-Ag ACIGS absorber layers, may explain the dependence of Nnet on I/III, whilst the meta-stable variations in Nnet are attributed to a currently unknown bulk defect. VOC losses after lightsoaking are also attributed to a meta-stable defect, with one candidate being the GaI antisite. Considering the full range of absorber compositions evaluated, an AAC of 0.2 is seen to provide the best balance between performance and stability for our high-Ga devices.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2025. p. 96
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2481
Keywords
(Ag, Cu)(In, Ga)Se2, Cu(In, Ga)Se2, Stability, Wide-Gap Chalcopyrite, Metastability, Capacitance Measurements, Admittance Spectroscopy
National Category
Other Materials Engineering
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-544453 (URN)978-91-513-2329-9 (ISBN)
Public defence
2025-02-07, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, 751 03, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2025-01-16 Created: 2024-12-04 Last updated: 2025-01-16

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Pearson, PatrickKeller, JanStolt, LarsEdoff, MarikaPlatzer Björkman, Charlotte

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