uu.seUppsala University Publications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rear Surface Optimization of CZTS Solar Cells by Use of a Passivation Layer With Nanosized Point Openings
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. Uppsala Univ, Angstrom Solar Ctr, S-75121 Uppsala, Sweden.;Univ Leuven, Dept Elect Engn, B-3001 Leuven, Belgium.;IMEC, Thin Film Photovolta, B-3001 Leuven, Belgium..
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Show others and affiliations
2016 (English)In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 6, no 1, p. 332-336Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

Previously, an innovative way to reduce rear interface recombination in Cu(In, Ga)(S, Se)(2) (CIGSSe) solar cells has been successfully developed. In this work, this concept is established in Cu-2(Zn, Sn)(S, Se)(4) (CZTSSe) cells to demonstrate its potential for other thin-film technologies. Therefore, ultrathin CZTS cells with an Al2O3 rear surface passivation layer having nanosized point openings are fabricated. The results indicate that introducing such a passivation layer can have a positive impact on open-circuit voltage (V-OC; +17% rel.), short-circuit current (J(SC); +5% rel.), and fill factor (FF; +9% rel.), compared with corresponding unpassivated cells. Hence, a promising efficiency improvement of 32% rel. is obtained for the rear passivated cells.

Place, publisher, year, edition, pages
2016. Vol. 6, no 1, p. 332-336
Keywords [en]
Aluminum oxide, Cu(In, Ga)(S, Se)(2), Cu-2(Zn, Sn)(S, Se)(4), nanosized point contacts, solar cells, surface passivation layer, thin-film
National Category
Environmental Engineering
Identifiers
URN: urn:nbn:se:uu:diva-274909DOI: 10.1109/JPHOTOV.2015.2496864ISI: 000367251900048OAI: oai:DiVA.org:uu-274909DiVA, id: diva2:898268
Funder
Swedish Research CouncilSwedish Energy AgencyEU, FP7, Seventh Framework Programme, 300998EU, FP7, Seventh Framework Programme, 327367Available from: 2016-01-27 Created: 2016-01-26 Last updated: 2018-08-12Bibliographically approved
In thesis
1. Annealing of Cu2ZnSn(S,Se)4 Thin Films: A Study of Secondary Compounds and Their Effects on Solar Cells
Open this publication in new window or tab >>Annealing of Cu2ZnSn(S,Se)4 Thin Films: A Study of Secondary Compounds and Their Effects on Solar Cells
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Kesterite Cu2ZnSnS4 (CZTS) is interesting as a sustainable photovoltaic technology due to its earth-abundant elements and suitable semiconducting properties. To date, a record efficiency of 12.6% has been achieved but further improvements are required to reach high efficiency for industrial implementation. Among the limiting issues is the understanding of the annealing process, which is crucial in promoting high material quality. In particular, the knowledge of the effects of segregated secondary compounds on solar cell performance is lacking.

In contrast to formation of ZnS particles throughout CZTS film, it is notable that SnS forms and usually segregates on the CZTS top and rear surfaces. The influence of SnS on CZTS solar cells was studied by electron beam induced current measurements. It is found that SnS presence on the CZTS surfacecan introduce “dead area”, whereas it seems beneficial for solar cell current when accumulates on the CZTS rear. For SnS passivation and from investigation of the passivation effect from an Al2O3 thin layer at the CZTS rear, improvement in overall device performance could not be demonstrated, due to either poor CZTS bulk or non-optimal device structure. The limitation in CZTS bulk quality was shown from a thickness study where carrier collection saturated already about 700-1000 nm CZTS thickness.

Formation of SnS alongside CZTS implies the anneal is limited by a deficient sulfur partial pressure (PS2). By looking into Sn-S phase transformations in SnS2 films after annealing, we find that PS2 drops rapidly over the annealing time, which could be well-correlated to a series of changes in CZTS material quality including secondary phase formations and defect modifications. It is shown that annealing CZTS under sufficiently high PS2 is critical for CZTS solar cells with high open circuit voltage (upto 783mV was reached), possibly due to the defect modification.

Besides SnS, it is observed that NaxS compounds are also readily formed on CZTS surfaces, due to Na diffusion from the glass substrate during annealing. NaxS negatively affects the formation of the CdS/CZTS interface during chemical bath deposition. It can be removed by an oxidation process or wet chemical etching.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 85
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1476
Keywords
Annealing, sputtering, thin film, CZTS, secondary phases, solar cell
National Category
Engineering and Technology
Research subject
Engineering Science
Identifiers
urn:nbn:se:uu:diva-314975 (URN)978-91-554-9817-7 (ISBN)
Public defence
2017-03-31, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2017-03-10 Created: 2017-02-07 Last updated: 2018-09-14
2. The Multiple Faces of Interfaces: Electron microscopy analysis of CuInSe2 thin-film solar cells
Open this publication in new window or tab >>The Multiple Faces of Interfaces: Electron microscopy analysis of CuInSe2 thin-film solar cells
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The CIS solar cell family features both a high stability and world-class performances. They can be deposited on a wide variety of substrates and absorb the entire solar spectrum only using a thickness of a few micrometers. These particularities allow them to feature the most positive Energy returned on energy invested (EROI) values and the shortest Energy payback times (EPBT) of all the main photovoltaic solar cells. Using mainly electron microscopy characterization techniques, this thesis has explored the questions related to the interface control in thin-film photovoltaic solar cells based on CuInSe2 (CIS) absorber materials. Indeed, a better understanding of the interfaces is essential to further improve the solar cell conversion efficiency (currently around 23%), but also to introduce alternative substrates, to implement various alloying (Ga-CIS (CIGS), Ag-CIGS (ACIGS)…) or even to assess alternative buffer layers.

The thread of this work is the understanding and the improvement of the interface control. To do so, the passivation potential of Al2O3 interlayers has been studied in one part of the thesis. While positive changes were generally measured, a subsequent analysis has revealed that a detrimental interaction could occur between the NaF precursor layer and the rear Al2O3 passivation layer. Still within the passivation research field, incorporation of various alkali-metals to the CIS absorber layer has been developed and analyzed. Large beneficial effects were ordinarily reported. However, similar KF-post deposition treatments were shown to be potentially detrimental for the silver-alloyed CIGS absorber layer. Finally, part of this work dealt with the limitations of the thin-barrier layers usually employed when using steel substrates instead of soda-lime glass ones. The defects and their origin could have been related to the steel manufacturing process, which offered solutions to erase them.

Electron microscopy, especially Transmission electron microscopy (TEM), was essential to scrutinize the local changes occurring at the different interfaces within a few nanometers. The composition variation was measured with both Electron energy loss spectroscopy (EELS) and Energy dispersive X-ray spectroscopy (EDS) techniques. Finally, efforts have been invested in controlling and improving the FIB sample preparation, which was required for the TEM observations in our case.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 85
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1701
Keywords
Electron microscopy, TEM, STEM, EELS, EDS, solar cells, CIGS, ACIGS, CZTS, post deposition treatment, KF, RbF, buffer layers, interfaces, inter layers, barrier layers, passivation layers
National Category
Energy Systems Other Electrical Engineering, Electronic Engineering, Information Engineering Other Materials Engineering
Research subject
Engineering Science with specialization in Materials Science; Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-357127 (URN)978-91-513-0402-1 (ISBN)
Public defence
2018-09-28, Polhemssalen, The Angstrom laboratory, Lägerhyddsvägen 1, Uppsala, 09:30 (English)
Opponent
Supervisors
Available from: 2018-09-07 Created: 2018-08-12 Last updated: 2018-10-02

Open Access in DiVA

No full text in DiVA

Other links

Publisher's full text

Authority records BETA

Vermang, BartRen, YiDonzel-Gargand, OlivierFrisk, ChristopherPlatzer-Bjorkman, CharlotteEdoff, Marika

Search in DiVA

By author/editor
Vermang, BartRen, YiDonzel-Gargand, OlivierFrisk, ChristopherPlatzer-Bjorkman, CharlotteEdoff, Marika
By organisation
Solid State Electronics
In the same journal
IEEE Journal of Photovoltaics
Environmental Engineering

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 785 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf