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 EVALUATION DU POTENTIEL DE CONCENTRATEURS A QUANTUM DOTS POUR LA PRODUCTION D’ELECTRICITE PHOTOVOLTAÏQUE Annual Report 2007 Author and Co-Authors Dr. Andreas Schüler, André Kostro, Benjamin Huriet Institution / Company Ecole Polytechnique Fédérale de Lausanne EPFL, Laboratoire d’Energie Solaire et de Physique du Bâtiment LESO-PB Address Bâtiment LE, Station 18, 1015 Lausanne Telephone, E-mail, Homepage +41 21 693 45 44, andreas.schueler@epfl.ch, http://lesowww.epfl.ch Project- / Contract Number 101806 / 152225 Duration of the Project (from – to) 01.11.2006 - 30.06.2007 Date January 2008 ABSTRACT One of the most promising application of semiconductor nanostructures in the field of photovoltaics might be planar photoluminescent concentrators. Even for diffuse solar radiation considerable concentration factors might be achieved. Such devices have originally been designed on the basis of organic dyes and might benefit from a considerably improved lifetime when replacing the organic fluorescent substances by inorganic semiconductor nanocrystals, so-called quantum dots. Quantum dot containing nanocomposite thin films are synthesized at EPFL-LESO by a low cost sol-gel process. In order to study the potential of the use of quantum dot solar concentrators in photovoltaic solar energy conversion, reliable computer simulations are needed. A tool for ray tracing simulations of quantum dot solar concentrators has been developed at EPFL-LESO on the basis of Monte-Carlo methods that are applied to polarization-dependent reflection/transmission at interfaces, photon absorption by the semiconductor nanocrystals and photoluminescent reemission. Together with the knowledge on the optoelectronical properties of suitable photovoltaic cells, such simulations allow to predict the total efficiency of the envisaged concentrating PV systems, and to optimize pane dimensions, photoluminescent emission frequencies, and choice of PV cell types. Seite 227 von 288
Introduction / Project Goals One of the most promising applications of semiconductor nanocrystals in the field of photovoltaics might be planar photoluminescent concentrators. Even for diffuse solar radiation considerable concentration factors can be achieved. Typical concentration factors for Compound Parabolic Concentrators (CPCs based on parabolic mirrors) are in the order of 2 [12], while for fluorescent planar solar concentrators typical concentration factors above 30 have been predicted [5]. Such devices have originally been designed on the basis of organic dyes [8], and will benefit from a considerably improved lifetime when replacing the organic fluorescent substances by inorganic semiconductor nanocrystals, socalled quantum dots [4,7]. Additionally, the tunability of the optical properties by the size of the nanocrystals provides a large amount freedom for the design and optimization of such devices. A schematic drawing of the principle of fluorescent solar concentrators proposed by Goetzberger is shown in Fig.1(a). One or several waveguides are fabricated from panes of transparent media doped with fluorescent dyes. Incoming solar radiation is absorbed in the volume of the waveguides, and isotropically reemitted by fluorescence. A large part of the emitted radiation is captured by total internal reflection and propagates to the edges. The likewise concentrated radiation is converted by photovoltaic cells with band gaps matching the wavelengths of the spectral emission lines of the photoluminescent materials. By choosing dyes with suitable absorption and emission properties, stacks of fluorescent collectors can be designed, with absorption edges chosen in a manner similar to multi-junction photovoltaic cells. Due to this step-like absorption edge/band-gap matching, the conversion efficiency can be higher than for single-junction devices. The same geometry has been used in quantum dot solar concentrators [4, 7], where photoluminescent semiconductor nanocrystals replace the fluorescent dyes. Instead of immersing quantum dots in transparent resins, we propose to deposit quantum dot containing silicon dioxide films on highly transparent low iron glass substrates by sol-gel dip-coating. If the refractive index of the coating is close to the one of the substrate, internal reflection occurs mainly at the surface of the coating, as depicted in Fig1 (b). For clarity, the thickness of the coating is exaggerated in the representation. (a) (b) Fig. 1: Quantum dots immersed in bulk of panes (a), and contained within a coating applied to the glass. Fig. 2 shows a photograph of CdS nanocrystal containing SiO2 coatings produced by low-cost sol-gel dip-coating at EPFL-LESO [1]. The samples were annealed at 250°C, 350°C, and 450°C. The strong emission from the edges of the samples is due to the concentration of the photoluminescent radiation in the waveguides by total internal reflection. The obtained colors of the visible photoluminescence, ranging from green for 250°C to yellow for 350°C and orange for 450°C, illustrate the effects of quantum confinement. The size distribution of the nanocrystals depends on the annealing temperature during the self-organized crystal growth. The three-dimensional quantum confinement in the quantum dots induces a discretization of electronic states, very much like in atoms or molecules. The resulting optical properties depend on the crystal size and can thus be tuned by varying the dimensions of the nanocrystals (and thus by varying the annealing temperature). Important parameters are the internal quantum yield (number of photons emitted from nanocrystal divided by the number of photons absorbed by the nanocrystal), and the external quantum yield (number of photons arriving at PV cell surface divided by the number of photons taken up by the concentrator). The photovoltaic concentration of a single fluorescent pane can be defined as the ratio of the electrical power produced by the cell when being illuminated with the concentrated radiation and the electrical power produced by the cell when being illuminated with the AM1.5 global spectrum. Seite 228 von 288 Evaluation du potentiel de concentrateurs à quantum dots pour la production d’électricité photovoltaïque, A. Schüler, EPFL 2/9
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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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3/9 Fig. 1: Refractive index n and
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5/9 V oc [mV] 940 920 900 880 860 8
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7/9 Fig. 5: Top) SEM micrographs of
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9/9 Acknowledgements The co-workers
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Seite 40 von 288 Introduction and f
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Seite 42 von 288 Introduction / Pro
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Seite 44 von 288 Results The amorph
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Seite 50 von 288 High efficiency so
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Seite 52 von 288 Towards low costs
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Eidgenössisches Departement für U
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3/6 The Athlet consortium comprises
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5/6 Large area cluster deposition s
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SIWIS Département fédéral de l
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3/6 Results Defects characterizatio
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5/6 The test methodology was optimi
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Seite 70 von 288 Summary of Applied
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Seite 72 von 288 Table 5 summarizes
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3/7 Figure 1: Vacuum deposition equ
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5/7 Testing of thickness, chemical
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7/7 Figure 6: Large area flexible s
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Seite 86 von 288 Intensity / arb. u
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LARCIS Eidgenössisches Departement
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3/6 Work and results Alternative Ba
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5/6 As expected the addition of Na
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ATHLET Eidgenössisches Departement
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3/9 ZnO:Al/ZnO was deposited by rf-
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5/9 Figure 4: XRD pattern of powder
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7/9 PBDVA temp [°C] 100 200 250 Bu
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9/9 National and international coll
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Introduction / Project Goals Thin f
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Introduction The work to be reporte
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Ongoing Work and Results 2007 Dye d
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International Cooperation Internati
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Introduction Dye-sensitized solar c
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Figure 2: Upper panel: isodensity p
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3/3 (a) (b) I N ClO ClO4- 4- Al ITO
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Seite 124 von 288 Project Goals The
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Seite 130 von 288 National and inte
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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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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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