Programm Photovoltaik Ausgabe 2008 ... - Bundesamt für Energie BFE

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Eidgenössisches Departement für Umwelt, Verkehr, Energie und Kommunikation UVEK Bundesamt für Energie BFE THIN FILM CIGS SOLAR CELLS WITH A NOVEL LOW COST PROCESS Annual Report 2007 Author and Co-Authors A. N. Tiwari, M. Kälin Institution / Company ETH Zürich Address Thin Film Physics Group, Technoparkstr. 1, 8005 Zürich Telephone, E-mail, Homepage +41 44 633 79 49, tiwari@phys.ethz.ch, http://www.tfp.ethz.ch Project- / Contract Number 100964 / 152223 Duration of the Project (from – to) 01.11.2006 - 31.10.2008 Date 17.12.2007 ABSTRACT A novel low-cost process for the production of thin film Cu(In,Ga)Se2 solar cells using an ion exchange reaction in liquid solutions is developed. The process involves the deposition of a In2Se3 or (In,Ga)Se2 precursor layer, a step for low temperature in-diffusion of copper atoms and further thermal annealing in selenium containing atmosphere where the precursor is converted to the Cu(In,Ga)Se2 compound. Efficiencies up to 4.1% were obtained in the first phase of the project. Seite 83 von 288
Seite 84 von 288 Introduction / Project Goals High efficiency Cu(In,Ga)Se2 solar cells can be produced from (In,Ga)2Se3 precursor films using the three stage process [1]. In the second stage of this process, the (In,Ga)2Se3 films are exposed to a flux of Cu and Se atoms at temperatures >540°C, leading to the formation of Cu(In,Ga)Se2 and Cu2Se. The current record efficiency Cu(In,Ga)Se2 solar cells (19.5%) were produced using this method [2]. Work performed with In2Se3 has shown that Cu vapour can be diffused into In2Se3 layers at 200°C [3]. In this case a subsequent high temperature annealing stage in the presence of Se vapour was used to produce CuInSe2 layers that gave solar cell efficiencies of 13.7%. Other solar cell technologies have made use of low temperature (�100°C) copper ion exchange reactions to incorporate copper into thin films. Most notable perhaps is the Clevite process used to make CdS/Cu2S solar cells. In this process Cu + ions in an aqueous solution of CuCl exchange places with Cd 2+ ions in a CdS layer to form a surface layer of Cu2S [4]. A similar process (from aqueous Cu(NO3)2 solution) has been used to incorporate Cu into CdTe solar cells, leading to the formation of CuTe and excess Cu. In this case, the layers were annealed at high temperature after immersion in the copper solution to promote further diffusion. The objective of this work is to develop a novel low-cost process for the production of thin film Cu(In,Ga)Se2 solar cells. The ion-exchange reaction will be used to incorporate copper ions into thin films of indium selenide from aqueous solution. These layers will then be homogenised by annealing at high temperature in the presence of selenium vapour, leading to the formation of chalcopyrite CuInSe2. Further, the process idea will be protected by a patent. Work performed and results obtained 700-800nm thick indium selenide films were deposited onto 5x5cm 2 molybdenum-coated soda lime glasses substrates by co-evaporation. Deposition of the indium selenide films was performed at 450°C. Due to the style of sample holder, an uncoated border of Mo was left around the edge of each substrate. Graded copper-indium-selenium precursor films were prepared by suspending the indium selenide layers in an aqueous solution of CuSO4 (0.2M) and acetic acid (0.2M) for 1 hour. The acetic acid was required to prevent the formation of copper hydroxide precipitates. The solutions were stirred constantly and heated from room temperature to boiling point whilst the indium selenide films were immersed. After immersion in the copper solution the films were rinsed thoroughly in deionised water and dried. Films were selenized in a two-zone tube furnace under flowing N2 and selenium vapour. The two zones allowed the temperature of the selenium source to be controlled separately from the temperature of the substrate. Typically the substrate was ramped to 575°C whilst the Se source was maintained at 400°C. After selenization films were etched in aqueous potassium cyanide solution (10%ww) for 30 seconds. One such indium selenide film was quartered after deposition and each quarter was analysed by XRD and XPS at different stages of processing. The “As-Deposited” quarter was left as In2Se3, the “Cu-Treated” quarter was analysed after immersion in the Cu-solution, the “Selenized” sample was analysed after selenization and the “Etched” sample was analysed after KCN etching. Another indium selenide film was processed into solar cells after completion of the above steps by deposition of a CdS buffer layer by chemical bath deposition and a ZnO and ZnO:Al bilayer window by RF sputtering. IV measurements were performed under a tungsten-filament lamp calibrated against a crystalline silicon reference cell. During immersion in the copper solution the Mo exposed around the border of the samples was removed from the substrate. This is due to oxidation of the Mo into soluble molybdenum oxide. When viewed through the substrate glass, it was evident that areas of the Mo beneath the In2Se3 had been removed as well. This is thought to be due to pin holes in the In2Se3 layers (themselves potentially due to defects in the Mo film) allowing contact between the solution and the Mo. This degradation of the back contact limited the thickness of the In2Se3 layers into which relevant quantities of copper could be incorporated. Thin Film CIGS Solar Cells with a Novel Low Cost Process, A. N. Tiwari, ETHZ 2/5
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Forschung, April 2008 Programm Phot
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Programm Photovoltaik Ausgabe 2008
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T. Meyer ORGAPVNET: Coordination Ac
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PROGRAMM PHOTOVOLTAIK Eidgenössisc
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1. Programmschwerpunkte und anvisie
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Ein neues KTI-Projekt Flexible Phot
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In einem neuen, durch den Axpo Natu
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Performanz und Energieproduktion vo
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ERGÄNZENDE PROJEKTE UND STUDIEN En
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in diesem Projekt für die Koordina
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5. Pilot- und Demonstrationsprojekt
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Produktionskapazität von insgesamt
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[26] H. Häberlin, L. Borgna, D. Gf
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[89] Konzept der Energieforschung d
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Solarzellen C. Ballif, J. Bailat, F
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Département fédéral de l’envir
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Project Goals The goal is the estab
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NAPOLYDE Département fédéral de
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3/7 � PECVD/Sputtering Co-deposit
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5/7 Work and results SP2.4 - Nanola
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7/7 Evaluation 2007 and Outlook 200
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Projektziele In der Schweiz bestehe
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Die wichtigsten erreichten Ziele de
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Energy Center (EC) der EPFL Univers
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Für 2008 ist in Zusammenarbeit mit
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BIPV-CIS Eidgenössisches Departeme
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3/3 Bewertung 2007 und Ausblick 200
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3/9 Service measurements In 2007 a
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5/9 Type of meas. Direct with c-Si
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7/9 c-Si reference cell for the mea
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9/9 � 4 energy rating comparison
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1. Traceable performance measuremen
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The following list shows the measur
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data sets. The indoor data sets con
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The blind round-robin proved that o
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Einleitung / Projektziele Herstelle
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Abb. 1, und deren Mittelwert für d
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Aus Gleichung (1) ergeben sich der
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Abb. 7: Abhängigkeit des Wirkungsg
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Projektziele für 2007 � Ununterb
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Generator-Korrekturfaktor k G in %
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WR-Defekte pro WR-Betriebsjahr 0.8
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Nationale / internationale Zusammen
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Einleitung / Projektziele Dezentral
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BON: Betrieb ohne Netz oder USV-Bet
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PV-BUK Eidgenössisches Departement
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Internationale Koordination P. Hüs
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3/3 Turbidity climatology Turbidity
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Einleitung / Projektziele Normenarb
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IEC 62548 Installation and Safety R
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Referenzen Eine vollständige Liste
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Introduction and Goals PV ERA NET i
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WP2: Strategy Issues: The main acti
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A dedicated transnational call “P
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Databases have been developed for o
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