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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.
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2016 (English)In: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 6, no 1, 332-336 p.Article 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, 332-336 p.
Keyword [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: diva2:898268
Funder
Swedish Research CouncilSwedish Energy AgencyEU, FP7, Seventh Framework Programme, 300998EU, FP7, Seventh Framework Programme, 327367
Available from: 2016-01-27 Created: 2016-01-26 Last updated: 2017-11-30Bibliographically 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. 85 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1476
Keyword
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)
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Available from: 2017-03-10 Created: 2017-02-07 Last updated: 2017-03-20

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

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