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ABSTRACT: We study the impact of the residual surface morphology resulting from rear side wet chemical polishing of initially random pyramid textured surfaces on large area industrial rear surface thermal oxide passivated Cz Si solar cells. Cell
parameters for three different surfaces (low, medium and high removal of Si) and a fully textured rear surface as reference are presented for solar cells with rear sides metallized either by physical vapour deposition or by screen printing technique. For both metallization schemes a flattened surface clearly results in higher values for open circuit voltage and short circuit current density and thus also cell efficiency. Median efficiencies up to 19.4 % (239 cm², as processed) and stabilized peak efficiency of 19.3 % (confirmed by Fraunhofer ISE CalLab) are reached. Carrier lifetime and quantum efficiency measurements confirm that the rear surface recombination and injection dependence strongly reduces for flattened surfaces, which is attributed to changes in crystal orientation and reduced surface area.
Energy Procedia 01/2012; 27:573-9.
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E. Lohmuller,
B. Thaidigsmann,
M. Pospischil,
U. Jager,
S. Mack,
J. Specht, J. Nekarda,
M. Retzlaff,
A. Krieg,
F. Clement,
A. Wolf,
D. Biro,
R. Preu
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ABSTRACT: We present metal wrap through passivated emitter and rear solar cells (MWT-PERC) on monocrystalline p-type silicon featuring laser-doped selective emitter structures in combination with either screen-printed (SP) or more advanced dispensed front side contacts. Thermally grown silicon oxide layers serve as emitter and rear surface passivation. Laser-fired contacts connect the SP aluminum rear contact to the silicon base. The rear side features solder contacts for both polarities. Conversion efficiency values of 20.6% for float-zone and 20.1% for Czochralski-grown silicon (not stabilized) are achieved on large-area cells with 149 wafer size. These are within the highest values reported for large-area p-type silicon solar cells to date. Analytical modeling enables a consistent description of the devices and allows for determining the dominating loss mechanisms.
IEEE Electron Device Letters 01/2012; · 2.85 Impact Factor
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ABSTRACT: This work presents the first results for the production of highly efficient solar cells with industrial processes using the PERC structure. Two batches of FZ and Cz wafers were conducted to prove the applicability of a transfer from the clean room to an industrial standard. The front and rear side metallization was done by a new pilot system using the sputtering technology. The investigation of solar cell results, series resistance, contact resistance and a optical analysis are discussed later on.
Photovoltaic Specialists Conference (PVSC), 2010 35th IEEE; 07/2010
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ABSTRACT: The contact formation on high efficiency solar cells using a high temperature process is the subject of this research. The chemical reactions between ink components and solar cell during the contact firing process are studied in detail by thermal gravimetric - differential thermo analysis. The mechanism behind the etching process and the opening of the dielectric layer are explained and the impact of the glass frit is investigated. Based on these studies, a seed layer ink was developed, optimized and tested on silicon solar cells. The developed ink was applied on high efficiency solar cells with printed front and rear contacts. At the rear side, we used a firing stable passivation layer consisting of Al<sub>2</sub>O<sub>3</sub> and SiN<sub>x</sub>, which additionally resists the reactive compounds of the screen printed Al-paste. After applying laser fired contacts at the rear and light induced silver plating at the front, cell efficiencies of η = 21% and fill factors of 81% could be measured.
Photovoltaic Specialists Conference (PVSC), 2010 35th IEEE; 07/2010
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ABSTRACT: In today´s market, crystalline silicon wafer technology dominates industrial solar cell production. Common devices feature opposing electrodes that are situated at the front and rear surface of the wafer and subsequent front-to-rear interconnection is used for module assembly. This paper reflects the functions which have to be fulfilled for the back-side contact of the solar cell as well as challenges and advances for the two basic classes: full-area and local rear contact formation. While full-area contacting has proven to be a reliable technology for industrial production, local contacting through dielectric layers has yet to be put through its paces in industrial implementation.
Photovoltaics International. 01/2010; Edition 7(First quarter, February 2010):64-75.
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ABSTRACT: This work focuses on manufacturing inkjet structured Emitter Wrap-Through (EWT) silicon solar cells with a side selective emitter and an evaporated metallization. Inkjet structuring is a suitable technique for the formation of interdigitated structures used in back contacted silicon solar cells because it allows small feature sizes and has high alignment accuracy. Therefore all structuring steps in this EWT solar cell process are done with the help of inkjet masking. This includes the structuring of a silicon oxide passivation layer and the evaporated aluminum metallization. For all masking processes an acid-resistant inkjet hotmelt ink is used. An evaporated thick aluminum layer and laser-fired contacts (LFC) [1] to contact the bulk region are introduced. Cell efficiencies above 15% prior to a forming gas anneal are reached. The best cell reaches an efficiency of 15.7% after a short annealing step on a hotplate.
Proceedings of the 35th IEEE Photovoltaic Specialists Conference, Honolulu, Hawaii, USA; 01/2010
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ABSTRACT: In this paper we present first results concerning different thermal evaporation processes for thin aluminum layers, which are carried out on a pilot system with a throughput of up to 540 wafers/h (156 Ã 156 mm<sup>2</sup>). To qualify the processes the deposited aluminum layers were evaluated with respect to homogeneity and conductivity. Additionally the effect of the different processes on the passivation quality of a thermally grown 100 nm thick SiO<sub>2</sub> was analyzed by means of lifetime measurements, indicating a negligible effect of the conducted process variations on the passivation quality. Finally high-efficiency silicon solar cells were prepared to determine the overall potential and to compare it with an electron beam (e-gun) evaporation process, which is used as a standard process in our laboratory. An efficiency of up to 21% was achieved by the high deposition rate technique performing at least as well as our standard high efficiency process.
Photovoltaic Specialists Conference (PVSC), 2009 34th IEEE; 07/2009
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L. Gautero,
M. Hofmann,
J. Rentsch,
A. Lemke,
S. Mack,
J. Seiffe, J. Nekarda,
D. Biro,
A. Wolf,
B. Bitnar,
J.-M. Sallese,
R. Preu
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ABSTRACT: The market need for a lower price per Watt<sub>peak</sub> asks for the development of solar cell designs with a low production cost and a high performance. An approach to reach a high efficiency with a solar cell structure containing a diffused emitter on a p-type silicon wafer is the implementation of a PERC structure on the rear side. This structure gets advantageous to the standard screen printed solar cell when its production cost stays comparable to the latter and offers a higher efficiency. Since this technique can inherently be applied to thinner wafers, an additional advantage comes from the reduced material consumption. The purpose of this work is to introduce a production sequence able to create a PERC structure on thin silicon wafers using steps available in the PV industry or at least close to industrial application. Applying this process on Czochralski (Cz) wafers of 120 μm thickness, a stable efficiency of 18.0 % was achieved.
Photovoltaic Specialists Conference (PVSC), 2009 34th IEEE; 07/2009
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ABSTRACT: In this paper we report about first results regarding laser fired contacts (LFC) on an optimized screen printed aluminium rear side layer and compare it with our "standard" LFC procedure on evaporated aluminium layers. Fist of all, the influence of the laser pulse energy, pulse duration and amount of pulses on the resistance of one contact is evaluated. Since this value depends strongly on the size of the contact also the recombination losses in the contact area have to be considered in order to compare and qualify LFC contacts comprehensively. We have achieved cell efficiencies > 18.0% on industrial like processed wafers, which underlines the potential of this approach. Finally, a 20.5 % efficiency solar cell with an aerosol printed front metallization manufactured on laboratory scale is presented, which is the best value ever reported for solar cells with fired front and back side metallization.
Proceedings of the 24th European Photovoltaic Solar Energy Conference, Hamburg, Germany; 01/2009
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L. Gautero,
J. Rentsch,
L. Weiss,
N. Kohn,
S. Eigner,
M. Zimmer,
J. Specht, J. Nekarda,
D. Stüwe,
M. Retzlaff,
D. Biro,
J.-M. Sallese,
R. Preu
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ABSTRACT: The industrial production of bulk silicon solar cells with high efficiency brings advantages as more efficient energy harvesting and better exploitation of materials. The candidate industrial approach conforms to good homogeneity on the whole designated active area as well as reproducible results on the local structuring, hence the scales span 4 order of length magnitude. The approaches used here are based on the improvement of the passivation of the dark side of the cell, employing a so called backside passivation layer (BSPL), this approach is compared to a reference screen printing of Aluminium paste and subsequent firing. The passivation mechanism of the deposited layer is affected by subsequent metallisation steps, some process sequences show with comparison to reference a loss in open circuit voltage and short circuit current, the fill factor can still be comparable. Cells realised with this approach are facing the constraints of the tools, adjustments of the process parameters will deliver the high efficiency that is targeted.
Proceedings of the 23rd European Photovoltaic Solar Energy Conference, Valencia, Spain; 01/2008
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Proceedings of the 23rd European Photovoltaic Solar Energy Conference, Valencia, Spain; 01/2008
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ABSTRACT: This work demonstrates the feasibility and usefulness of a new method to analyse the quality of the rear contact of silicon solar cells separated from other ohmic loss channels as e.g. the resistive loss in the front contact grid. The measurement is based on SunsVoc data at high illumination densities between 1 and 1000 suns. Generally the rear contacts can be described as a Schottky diode with a shunt resistor in parallel. At 1 sun operation conditions the back contact is fully dominated by the shunt showing an ohmic behaviour. However, at high illumination densities the Schottky diode can not be shunted completely anymore resulting in an increasing voltage which is opposed to the pn junction voltage. Finally a reversal point in the SunsVoc characteristics can be observed, i.e. the voltage decreases with increasing illumination density. The evaluation of this characteristic behaviour is used to extract physical parameters like the barrier height of the contact. Additionally the contact quality is assessed for different contact types and base doping concentrations. The predicted contact quality is in good correlation with the measured fill factors of the cells.
22nd European Photovoltaic Solar Energy Conference, Milan, Italy; 01/2007
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Fraunhofer ISE.
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Fraunhofer ISE.
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Matthias Hörteis,
J. Benick, J. Nekarda,
A. Richter,
Ralf Preu,
S.W. Glunz,
Elias Urrejola,
Kristian Peter,
Joachim Glatz-Reichenbach,
Eckhard Wefringhaus, [......],
B.-J. Godejohann,
Frank Heinemeyer,
Christoph Mader,
Daniel Münster,
Thorsten Dullweber,
N.-P. Harder,
Rolf Brendel,
Dirk Reinwand,
Philip Hartmann,
P. Grunow
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ABSTRACT: Metallization is one of the key process steps to fabricate solar cells with high performance in a cost-effective way. More than 85% of the photovoltaic solar cell manufacturing uses thick film screen-print metallization to produce solar cells, but a lot of research is also carried out on alternative metallization schemes and/or variations to screen-printing. The success of metallization technology development is crucial for the evolution of solar cell technology towards lower production costs and higher efficiencies. Recognizing that existing photovoltaic events did not provide an ideal setting for experts to discuss these topics in detail, a dedicated and focused workshop on the topic of metallization of crystalline Si solar cells was organized in Utrecht, The Netherlands in 2008. The second edition was held in Constance, Germany on 14th and 15th of April 2010. Around 190 scientists and engineers from solar energy institutes, universities, and companies all over the world gathered in the "Konzil", a historical building facing the Lake of Constance, to share and discuss the latest developments in solar cell metallization. In this volume, selected contributions to the Second Metallization Workshop are published in scientific article form, enabling readers to obtain detailed information about specific contributions and to give proper reference to them. The articles were peer-reviewed by the members of the scientific committee of the workshop, consisting of well known and established experts in the field of metallization for crystalline silicon solar cell. The Second Workshop on Metallization of Crystalline Silicon Solar Cells provided excellent insights in the status and development of metallization technology. Although screen-printing has been around for a long time, it is efficient, quick and reliable, and its performance is being stretched by recent innovations, making it hard for alternative techniques to emerge. The hybrid Ag seed and plate approach is the only technique that could be introduced in the short term, but has lost some of its appeal because of improvements in traditional screen-printing. Metallization schemes based on Cu plating appear the ultimate solution in terms of line width, cell performance and material costs, but several hurdles need to be overcome before it can be widely adopted. Die Metallisierung von kristallinen Siliziumsolarzellen ist einer der Schlüsselprozesse in der Produktion von Hochleistungssolarzellen bei möglichst geringen Kosten. Obwohl rund 85% der weltweit hergestellten Solarzellen das etablierte Siebdruckverfahren nutzen, wird derzeit mit Hochdruck an der Weiterentwicklung desselben und an Alternativen geforscht. Diese Entwicklung wird zum Einen davon getrieben, dass die Herstellungskosten sinken, die Effizienz von Solarzellen aber steigen soll. Zum Anderen verlangt die Weiterentwicklung von etablierten als auch die Einführung von neuen Solarzellkonzepten neue Ansätze in der Metallisierung. Um eine Plattform für Wissenschaftler aus Universitäten, Instituten und der Industrie für einen intensiven Austausch über dieses Thema zu schaffen, wurde mit Erfolg 2008 in Utrecht in den Niederlanden ein erster internationaler Workshop zum Thema Metallisierung von kristallinen Siliziumsolarzellen organisiert. Der zweite Workshop dieser Art fand am 14. und 15. April 2010 in Konstanz statt. 190 Spezialisten und Wissenschaftler aus der ganzen Welt trafen sich im Konzil, einem historischen Gebäude direkt am Bodensee, um die aktuellsten Entwicklungen auf diesem Gebiet vorzustellen und zu diskutieren. In diesem Tagungsband werden ausgewählte Beiträge zum zweiten Metallisierungsworkshop in Form wissenschaftlicher Artikel veröffentlicht. Diese Beiträge wurden vom wissenschaftlichen Komitee ausgewählt und begutachtet. Das wissenschaftliche Komitee bestand aus international bekannten und etablierten Experten auf dem Gebiet der Metallisierung von kristallinen Siliziumsolarzellen. Auf dem Workshop wurde deutlich, dass die etablierte Technik der Siebdruckmetallisierung durch aktuelle Innovationen es neuen Ansätzen nach wie vor schwer macht, eine gewichtige Rolle in der industriellen Produktion von kristalline Siliziumsolarzellen zu spielen. Kurzfristig könnte eine Hybridtechnologie aus Silber-SaatschichtAufbringung und Silber-Plattierung an Bedeutung gewinnen, allerdings hat dieser Ansatz in den letzten zwei Jahren aufgrund der Fortschritte im Siebdruck etwas an Attraktivität verloren. Auf Kupfer basierende Metallisierungstechniken haben die größten Potentiale bezüglich Strukturbreiten, Solarzellenperformance und Kosten, allerdings sind noch einige wichtige Hürden zu nehmen, bevor diese Techniken im großen Maßstab eingesetzt werden können.
