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Uniformity assessment of a 6-inch Copper-Zinc-Tin-Sulfide solar cell sputtered from a quaternary compound target
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik. Midsummer AB, Elektronikhojden 6, SE-17143 Jarfalla, Sweden..
Midsummer AB, Elektronikhojden 6, SE-17143 Jarfalla, Sweden..
Midsummer AB, Elektronikhojden 6, SE-17143 Jarfalla, Sweden..
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
2015 (engelsk)Inngår i: 2015 IEEE 42ND PHOTOVOLTAIC SPECIALIST CONFERENCE (PVSC), 2015Konferansepaper, Publicerat paper (Fagfellevurdert)
Resurstyp
Text
Abstract [en]

Cu2ZnSnS4 solar cells are fabricated following an all-sputtering in line vacuum approach. 6-inch semi-square stainless steel substrates are used. A compositional and structural study of the absorber layer is conducted before and after annealing to assess the uniformity of both the sputtering and the annealing process. It is found that while the precursors are uniform both in morphology and composition, the annealing process introduces differences in grain size and metal content depending on the area considered on the 6-inch substrate. The corresponding solar cell is further divided into 184 small cells of 1 cm(2) to check the performance distribution across the device. Current-voltage characteristics and solar cell parameters are extracted. Natural convection inside the annealing chamber is suggested to affect significantly the heat distribution and a strong correlation between device performance and local temperature can be identified.

sted, utgiver, år, opplag, sider
2015.
Serie
IEEE Photovoltaic Specialists Conference, ISSN 0160-8371
Emneord [en]
photovoltaic cell, thin films, sputtering, annealing
HSV kategori
Identifikatorer
URN: urn:nbn:se:uu:diva-284901ISI: 000369992902063ISBN: 978-1-4799-7944-8 (tryckt)OAI: oai:DiVA.org:uu-284901DiVA, id: diva2:920988
Konferanse
IEEE 42nd Photovoltaic Specialist Conference (PVSC), JUN 14-19, 2015, New Orleans, LA
Tilgjengelig fra: 2016-04-19 Laget: 2016-04-19 Sist oppdatert: 2017-09-21bibliografisk kontrollert
Inngår i avhandling
1. Sputtering-based processes for thin film chalcogenide solar cells on steel substrates
Åpne denne publikasjonen i ny fane eller vindu >>Sputtering-based processes for thin film chalcogenide solar cells on steel substrates
2017 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Thin film chalcogenide solar cells are promising photovoltaic technologies. Cu(In,Ga)Se2 (CIGS)-based devices are already produced at industrial scale and record laboratory efficiency surpasses 22 %. Cu2ZnSn(S,Se)4 (CZTS) is an alternative material that is based on earth-abundant elements. CZTS device efficiency above 12 % has been obtained, indicating a high potential for improvement.

In this thesis, in-line vacuum, sputtering-based processes for the fabrication of complete thin film chalcogenide solar cells on stainless steel substrates are studied. CIGS absorbers are deposited in a one-step high-temperature process using compound targets. CZTS precursors are first deposited by room temperature sputtering and absorbers are then formed by high temperature crystallization in a controlled atmosphere. In both cases, strategies for absorber layer improvement are identified and implemented.

The impact of CZTS annealing temperature is studied and it is observed that the absorber grain size increases with annealing temperature up to 550 °C. While performance also improves from 420 to 510 °C, a drop in all solar cell parameters is observed for higher temperature. This loss is caused by blisters forming in the absorber during annealing. Blister formation is found to originate from gas entrapment during precursor sputtering. Increase in substrate temperature or sputtering pressure leads to drastic reduction of gas entrapment and hence alleviate blister formation resulting in improved solar cell parameters, including efficiency.

An investigation of bandgap grading in industrial CIGS devices is conducted through one-dimensional simulations and experimental verification. It is found that a single gradient in the conduction band edge extending throughout the absorber combined with a steeper back-grading leads to improved solar cell performance, mainly due to charge carrier collection enhancement.

The uniformity of both CIGS and CZTS 6-inch solar cells is assessed. For CZTS, the device uniformity is mainly limited by the in-line annealing process. Uneven heat and gas distribution resulting from natural convection phenomenon leads to significant lateral variation in material properties and device performance. CIGS solar cell uniformity is studied through laterally-resolved material and device characterization combined with SPICE network modeling. The absorber material is found to be laterally homogeneous. Moderate variations observed at the device level are discussed in the context of large area sample characterization.

Power conversion efficiency values above 15 % for 225 cm2 CIGS cells and up to 5.1 % for 1 cm2 CZTS solar cells are obtained.

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Upsaliensis, 2017. s. 107
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1564
Emneord
CIGS, CZTS, solar cell, photovoltaics, thin film, sputtering, annealing, gallium grading, blister, uniformity, stainless steel
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot elektronik
Identifikatorer
urn:nbn:se:uu:diva-329778 (URN)978-91-513-0078-8 (ISBN)
Disputas
2017-11-09, Polhemssalen, Ångström laboratory, Lägerhyddsvägen 1, Uppsala, 09:15 (engelsk)
Opponent
Veileder
Forskningsfinansiär
Swedish Foundation for Strategic Research Swedish Energy Agency
Tilgjengelig fra: 2017-10-17 Laget: 2017-09-21 Sist oppdatert: 2017-11-13

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