- Email: [email protected]
Large-area electrochromic glazing with ion-conducting PVB interlayer and two complementary electrodeposited electrochromic layers
ARTICLE IN PRESS
Solar Energy Materials & Solar Cells 90 (2006) 469–476 www.elsevier.com/locate/solmat
Large-area electrochromic glazing with ion-conducting PVB interlayer and two complementary electrodeposited electrochromic layers Alexander Kraft, Matthias Rottmann, Karl-Heinz Heckner Gesimat GmbH, Koepenicker Str. 325, 12555 Berlin, Germany Received 1 December 2004; accepted 11 January 2005 Available online 13 June 2005
Abstract A new laminated large-area electrochromic glass consisting of two FTO-coated glass panes coated with complementary electrochromic thin films by electrodeposition and laminated together by the use of an ion-conducting PVB sheet is presented. The visible light transmittance can be changed between 77% and 8% and the solar transmittance between 56% and 6%. r 2005 Elsevier B.V. All rights reserved. Keywords: Electrochromism; W oxide; Prussian blue; Polymer electrolyte; Smart windows; Optical properties
1. Introduction For more than 30 years, research efforts have been undertaken to develop largearea electrochromic glazing for architectural applications [1–6]. However, until recently, no reliable product has entered the market. This is mainly caused by cost, Corresponding author. Tel.: +49 30 65762609; fax: +49 30 65762608.
E-mail address: [email protected] (A. Kraft). 0927-0248/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2005.01.019
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performance and stability problems of the different devices and fabrication concepts which were considered so far [7–12]. The new concept of Gesimat [13] offers the possibility of a relatively low-cost production process, high switching range and long-term stability. This concept is based on the use of two complementary electrochromic layers prepared by electrodeposition in combination with an ion-conducting polymer electrolyte using polyvinyl butyral (PVB). The use of two complementary electrochromic layers instead of the combination of one electrochromic layer with a so-called ion-storage layer offers the possibility to switch between higher maximum and lower minimum transmittance with high coloration efficiency. PVB has been in use for laminated safety glass for about 60 years [14,15]. This is because of its unique properties such as high, adjustable adhesion to glass [16], high optical transparency, excellent toughness and flexibility, high impact strength and light and temperature resistance. The well-known technologies for the production of conventional PVB interlayers and for the production of laminated safety glass can now also be used for the manufacture of electrochromic glazings [13]. The electrochromic glass has physical properties similar to those of laminated safety glass.
2. Experimental The structure of the laminated electrochromic glass of Gesimat is shown in Fig. 1. Two sheets of FTO-coated glass (FTO—fluorine-doped tin oxide) with a thickness of 4 mm each are coated with complementary inorganic electrochromic layers. For this purpose, tungsten oxide (cathodic coloring, thickness about 800 nm) and Prussian Blue (anodic coloring, thickness about 500 nm) are chosen. Both are coated on FTO
glass FTO tungsten oxide ion conducting PVB Prussian Blue FTO glass
Fig. 1. Structure of the Gesimat electrochromic device.
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471
by cathodic electrodeposition from aqueous solutions. The electrodeposition of these materials has been described in the scientific literature (e.g. tungsten oxide [17] and Prussian Blue [18]). At the moment areas up to 1.2 m 0.8 m can be coated homogeneously by this method in our laboratory. The ion-conducting PVB interlayer (thickness 0.76 mm) is produced by extruding a mixture of the PVB polymer with plasticizer, Li ion-containing salt and some common polymer additives to a polymer sheet in a process similar to the extrusion of non-ion-conducting PVB interlayers for laminated safety glass. The two FTO-coated glass panes with tungsten oxide and Prussian Blue overlayers are laminated together via the ion-conducting PVB sheet under elevated temperature and pressure, either by vacuum bag process or by autoclaving [19]. Samples in the following sizes have been produced by this method: 10 cm 30 cm, 30 cm 30 cm, 30 cm 50 cm, 35 cm 50 cm, 50 cm 120 cm and 80 cm 120 cm. The solar transmittance curves of the electrochromic samples (size: 10 cm 30 cm) in the wavelength range of solar radiation at 20 1C were measured by T. Ha¨usler (Cottbus University) using a UV–VIS–NIR spectrometer (Perkin-Elmer Lambda 19). The solar transmittance Tsolar as well as the visible transmittance Tvis, were derived from the spectrometer data according to the European standard EN 410. For measuring the time-dependent transmittance, the bleaching and coloring processes were interrupted every 30 s for about 6 min measuring time. Current–time curves during switching of the electrochromic samples were recorded with a Voltalab PGZ301 potentiostat (Radiometer, Copenhagen). The ion conductivity of the ion-conducting PVB foils was derived from impedance measurements also performed with the Voltalab potentiostat.
3. Results and discussion Fig. 2 shows the temperature dependence of the ion conductivity of a PVB polymer electrolyte foil. As is common for polymer electrolytes, the conductivity strongly increases with increasing temperature. At room temperature, the ion conductivity is about 8 106 S/cm. Especially for large-area electrochromic glazing, this ion conductivity is high enough for an acceptable switching time of the electrochromic glass laminate for architectural applications. Transmittance spectra of the new electrochromic device in the fully bleached and colored states are shown in Fig. 3. A change of the visible light transmittance from about 8% in the colored to 77% in the bleached state is possible. High values for the photopic transmittance ratio (PTR ¼ Tvisbleached/Tviscolored) can also be achieved. Due to the use of two complementary electrochromic layers which both take part in the desired light-regulating effect, PTR is more than 9:1. The solar transmittance can be changed between 6% and 56%. Each intermediate state between the fully colored and bleached state can be adjusted. The reflectance of the electrochromic device does only slightly change during switching. This can be seen from Fig. 4, which shows the reflectance spectra of the electrochromic glass in the fully bleached and colored states. The visible reflectance
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ion conductivity/ S/cm
1x10 -4
1x10 -5
10 -6 240
260
280 300 320 temperature /K
340
360
380
Fig. 2. Temperature dependence of ion conductivity of the ion-conducting PVB sheet.
90 80
transmittance/%
70 bleached
60 50 40 30 20
colored 10 0 300 500
750 1000 1250 1500 1750 2000 2250 2500 wavelength /nm
Fig. 3. Transmittance spectra of the Gesimat electrochromic device in fully bleached and colored states.
changes from 9% in the bleached state to 6% in the colored state and the solar reflectance from 8% (bleached) to 7% (colored). The switching is performed by application of DC voltages between about 0.5 and 2.5 V. In the polarity with WO3 at the negative terminal and Prussian Blue at the positive terminal, the device is colored, by changing the polarity the device is bleached. During switching, the color changes from colorless transparent to blue and vice versa. If the voltage is switched off during switching at any coloration state, the momentary coloration state stays unchanged (memory effect). Therefore, electrical energy is required only during switching, not for maintaining a constant coloration
ARTICLE IN PRESS A. Kraft et al. / Solar Energy Materials & Solar Cells 90 (2006) 469–476
473
40 35
reflectance /%
30 25 20 15 10 5 0 300 500
750 1000 1250 1500 1750 2000 2250 2500 wavelength /nm
Fig. 4. Reflectance spectra of the Gesimat electrochromic device in fully bleached and colored states: dashed line, colored state; solid line, bleached state.
150 coloration: 1.4 V
2
1
current density/µA/cm2
100 50 0 -50 -100 -150 -200
bleaching: -1.4 V
0
200
400
600 800 time/sec
1000
1200
Fig. 5. Current density versus time during switching of laminated electrochromic glass samples in two different sizes: (1) 10 cm 30 cm, contact distance 10 cm, (2) 30 cm 30 cm, contact distance 30 cm (three (sample 1) or two (sample 2) switching cycles with 71.4 V).
state. This is due to the battery-like behavior of the electrochromic device [20]. For one full coloring or bleaching step between the maximum and minimum light transmittance, the energy consumption is approximately 200 W s/m2. The switching time strongly depends on the size of the electrochromic glass or more exactly on the distance of the outer electrical contacts (see also Fig. 1). Fig. 5 shows the current density–time relationship of three coloring–bleaching cycles of two electrochromic glass samples of different dimensions. As can be seen from this figure, with increasing distance between the electrical contacts (in this case from 10 to 30 cm), the
ARTICLE IN PRESS 474
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switching time also increases. However, the switching speed can be accelerated by the use of a newly developed advanced electronic control system. Fig. 5 also shows that bleaching is faster than coloring. This can also be seen from Figs. 6 and 7 which show the change of the transmittance spectra during coloring and bleaching. From Fig. 5, the high reversibility of the switching process is also obvious. Currently, several durability tests are performed with promising results [21]. The most severe tests are temperature cycle and simulated solar radiation tests. During these tests, the samples switch continuously between the bleached and colored states or are held permanently either in the bleached state or in the colored state and are at the same time subjected to changing temperature or to simulated solar radiation. The temperature stress performed consisted of one temperature cycle per day with temperature stages of +30, +80 and 25 1C, each for 4 h. For the simulated solar radiation tests, the samples were irradiated for up to 80 days by a special metal halide bulb which generates a spectrum with an irradiance of about 1000 W/m2, which is close to that of natural sunlight (AM 1.5) [21]. After 144 temperature cycles with up to 34,560 simultaneous bleaching/coloring cycles and also after 80 days (1,920 h) of simulated solar radiation with simultaneous up to 10,000 switching cycles, the changes in the dynamic electrical and optical properties of samples after both tests were below 10% compared to the properties before the tests [21]. Additionally, investigations on the heat transport inside the glazing and on thermal stresses which can be induced due to a partial shading of a colored electrochromic glazing during sunlight irradiation have been performed [22]. For the most effective use regarding energy consumption and glare protection of electrochromic glazing in architectural applications, the control strategy is very important. Recently, it has been found that a control strategy considering whether a room is in use or not can lead to large savings of the energy needed for space cooling
80 70 transmittance /%
60
0s
50 40 30 30 s
20 10 300 s 0 300 500
60 s
750 1000 1250 1500 1750 2000 2250 2500 wavelength /nm
Fig. 6. Change of the transmittance spectra during coloring with 1.4 V. Eleven transmission spectra recorded at intervals of 30 s switching time between 0 and 300 s.
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475
80 70 transmittance /%
60
180 s
50 40 30 20
120 s 0s
10 0 300 500
750 1000 1250 1500 1750 2000 2250 2500 wavelength /nm
Fig. 7. Change of the transmittance spectra during bleaching with 1.4 V. Seven transmission spectra recorded at intervals of 30 s switching time between 0 and 180 s.
[23,24]. The importance of the control strategy is also the result from tests with the new Gesimat electrochromic glazings [21,25]. For these tests the electrochromic glass was installed in a south-facing test facade. The experiments in this facade included energy saving and illuminance measurements at a desk at a distance of 1.5 m from the window.
4. Conclusions Since 1998, Gesimat is working on the development of a new laminated electrochromic glazing with the development focus on using low-cost technologies and/or state-of-the-art processes and materials of the glass-processing industry. The resulting new device and fabrication concept for an electrochromic window presented in this paper offers the possibility for a cost-effective production of large-area electrochromic glazing with high contrast ratio and long-term stability in the near future. Possible application areas include but are not limited to architectural and automotive smart glazings.
Acknowledgments We thank H. Stenzel (HT Troplast Troisdorf, Germany), M. Steuer and B. Papenfuhs (KSE GmbH Frankfurt/M., Germany) and T. Ha¨usler and U. Fischer (Department of Applied Physics, Brandenburg University of Technology Cottbus, Germany) for their collaboration during the development process. Part of this work was funded by the German Federal Ministry of Economics and Labour, Contract no. 0327233F.
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476
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
[22] [23] [24] [25]
C.M. Lampert, Solar Energy Mater. 11 (1984) 1–27. R.J. Mortimer, Chem. Soc. Rev. 26 (1997) 147–156. M. Green, Ionics 5 (1999) 161–170. R.D. Rauh, Electrochim. Acta 44 (1999) 3165–3176. D.R. Rosseinsky, R.J. Mortimer, Adv. Mater. 13 (2001) 783–793. C.G. Granqvist, E. Avendano, A. Azens, Thin Solid Films 442 (2003) 201–211. M.A. Habib, S.P. Maheswari, J. Appl. Electrochem. 23 (1993) 44–50. K.-C. Ho, T.G. Rukavina, C.B. Greenberg, J. Electrochem. Soc. 141 (1994) 2061–2067. H. Wittkopf, Glass processing days 1997, Conference Proceedings Book, pp. 299–303. A. Maccari, G. Macrelli, P. Polato, E. Poli, Sol. Energy 63 (1998) 217–229. J. Nagai, G.D. McMeeking, Y. Saitoh, Sol. Ener. Mater. Sol. Cell 56 (1999) 309–319. T. Kubo, T. Shinada, Y. Kobayashi, H. Imafuku, T. Toya, S. Akita, Y. Nishikitani, H. Watanabe, Solid State Ionics 165 (2003) 209–216. H. Stenzel, A. Kraft, K.-H. Heckner, M. Rottmann, M. Steuer, B. Papenfuhs, Glass processing days 2003, Conference Proceedings Book, pp. 423–426. J.D. Ryan, US Patent US2205020, 1940. W.O. Herrmann, German Patent DE690332, 1940. U. Keller, H. Mortelmans, Glass processing days 1999, Conference Proceedings Book, pp. 353–356. E.A. Meulenkamp, J. Electrochem. Soc. 144 (1997) 1664–1671. V.D. Neff, J. Electrochem. Soc. 125 (1978) 886–887. M.V. Russelt, Glass processing days 1997, Conference Proceedings Book, pp. 475–479. K.-H. Heckner, A. Kraft, Solid State Ionics 152–153 (2002) 899–905. T. Ha¨usler, U. Fischer, M. Rottmann, A. Kraft, K.-H. Heckner, Solar optical properties and daylight potential of electrochromic windows, Proceedings of the World Renewable Energy Congress VIII (WREC 2004), Denver, CO, USA, 2004. U. Fischer, T. Ha¨usler, H. Rogass, M. Rottmann, A. Kraft, K.-H. Heckner, Int. J. Thermophys. 25 (2004) 1299–1307. A. Azens, C.G. Granqvist, Proc. Soc. Photo-Opt. Instrum. Eng. 4458 (2001) 104–111. A. Azens, C.G. Granqvist, J. Solid State Electrochem. 7 (2003) 64–68. T. Ha¨usler, Transmittance and luminance measurements on electrochromic glazing, Proceedings of the International Lighting and Colour Conference, Cape Town, South Africa, 2003, pp. 102–106.
Solar Energy Materials & Solar Cells 90 (2006) 469–476 www.elsevier.com/locate/solmat
Large-area electrochromic glazing with ion-conducting PVB interlayer and two complementary electrodeposited electrochromic layers Alexander Kraft, Matthias Rottmann, Karl-Heinz Heckner Gesimat GmbH, Koepenicker Str. 325, 12555 Berlin, Germany Received 1 December 2004; accepted 11 January 2005 Available online 13 June 2005
Abstract A new laminated large-area electrochromic glass consisting of two FTO-coated glass panes coated with complementary electrochromic thin films by electrodeposition and laminated together by the use of an ion-conducting PVB sheet is presented. The visible light transmittance can be changed between 77% and 8% and the solar transmittance between 56% and 6%. r 2005 Elsevier B.V. All rights reserved. Keywords: Electrochromism; W oxide; Prussian blue; Polymer electrolyte; Smart windows; Optical properties
1. Introduction For more than 30 years, research efforts have been undertaken to develop largearea electrochromic glazing for architectural applications [1–6]. However, until recently, no reliable product has entered the market. This is mainly caused by cost, Corresponding author. Tel.: +49 30 65762609; fax: +49 30 65762608.
E-mail address: [email protected] (A. Kraft). 0927-0248/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2005.01.019
ARTICLE IN PRESS 470
A. Kraft et al. / Solar Energy Materials & Solar Cells 90 (2006) 469–476
performance and stability problems of the different devices and fabrication concepts which were considered so far [7–12]. The new concept of Gesimat [13] offers the possibility of a relatively low-cost production process, high switching range and long-term stability. This concept is based on the use of two complementary electrochromic layers prepared by electrodeposition in combination with an ion-conducting polymer electrolyte using polyvinyl butyral (PVB). The use of two complementary electrochromic layers instead of the combination of one electrochromic layer with a so-called ion-storage layer offers the possibility to switch between higher maximum and lower minimum transmittance with high coloration efficiency. PVB has been in use for laminated safety glass for about 60 years [14,15]. This is because of its unique properties such as high, adjustable adhesion to glass [16], high optical transparency, excellent toughness and flexibility, high impact strength and light and temperature resistance. The well-known technologies for the production of conventional PVB interlayers and for the production of laminated safety glass can now also be used for the manufacture of electrochromic glazings [13]. The electrochromic glass has physical properties similar to those of laminated safety glass.
2. Experimental The structure of the laminated electrochromic glass of Gesimat is shown in Fig. 1. Two sheets of FTO-coated glass (FTO—fluorine-doped tin oxide) with a thickness of 4 mm each are coated with complementary inorganic electrochromic layers. For this purpose, tungsten oxide (cathodic coloring, thickness about 800 nm) and Prussian Blue (anodic coloring, thickness about 500 nm) are chosen. Both are coated on FTO
glass FTO tungsten oxide ion conducting PVB Prussian Blue FTO glass
Fig. 1. Structure of the Gesimat electrochromic device.
ARTICLE IN PRESS A. Kraft et al. / Solar Energy Materials & Solar Cells 90 (2006) 469–476
471
by cathodic electrodeposition from aqueous solutions. The electrodeposition of these materials has been described in the scientific literature (e.g. tungsten oxide [17] and Prussian Blue [18]). At the moment areas up to 1.2 m 0.8 m can be coated homogeneously by this method in our laboratory. The ion-conducting PVB interlayer (thickness 0.76 mm) is produced by extruding a mixture of the PVB polymer with plasticizer, Li ion-containing salt and some common polymer additives to a polymer sheet in a process similar to the extrusion of non-ion-conducting PVB interlayers for laminated safety glass. The two FTO-coated glass panes with tungsten oxide and Prussian Blue overlayers are laminated together via the ion-conducting PVB sheet under elevated temperature and pressure, either by vacuum bag process or by autoclaving [19]. Samples in the following sizes have been produced by this method: 10 cm 30 cm, 30 cm 30 cm, 30 cm 50 cm, 35 cm 50 cm, 50 cm 120 cm and 80 cm 120 cm. The solar transmittance curves of the electrochromic samples (size: 10 cm 30 cm) in the wavelength range of solar radiation at 20 1C were measured by T. Ha¨usler (Cottbus University) using a UV–VIS–NIR spectrometer (Perkin-Elmer Lambda 19). The solar transmittance Tsolar as well as the visible transmittance Tvis, were derived from the spectrometer data according to the European standard EN 410. For measuring the time-dependent transmittance, the bleaching and coloring processes were interrupted every 30 s for about 6 min measuring time. Current–time curves during switching of the electrochromic samples were recorded with a Voltalab PGZ301 potentiostat (Radiometer, Copenhagen). The ion conductivity of the ion-conducting PVB foils was derived from impedance measurements also performed with the Voltalab potentiostat.
3. Results and discussion Fig. 2 shows the temperature dependence of the ion conductivity of a PVB polymer electrolyte foil. As is common for polymer electrolytes, the conductivity strongly increases with increasing temperature. At room temperature, the ion conductivity is about 8 106 S/cm. Especially for large-area electrochromic glazing, this ion conductivity is high enough for an acceptable switching time of the electrochromic glass laminate for architectural applications. Transmittance spectra of the new electrochromic device in the fully bleached and colored states are shown in Fig. 3. A change of the visible light transmittance from about 8% in the colored to 77% in the bleached state is possible. High values for the photopic transmittance ratio (PTR ¼ Tvisbleached/Tviscolored) can also be achieved. Due to the use of two complementary electrochromic layers which both take part in the desired light-regulating effect, PTR is more than 9:1. The solar transmittance can be changed between 6% and 56%. Each intermediate state between the fully colored and bleached state can be adjusted. The reflectance of the electrochromic device does only slightly change during switching. This can be seen from Fig. 4, which shows the reflectance spectra of the electrochromic glass in the fully bleached and colored states. The visible reflectance
ARTICLE IN PRESS 472
A. Kraft et al. / Solar Energy Materials & Solar Cells 90 (2006) 469–476
ion conductivity/ S/cm
1x10 -4
1x10 -5
10 -6 240
260
280 300 320 temperature /K
340
360
380
Fig. 2. Temperature dependence of ion conductivity of the ion-conducting PVB sheet.
90 80
transmittance/%
70 bleached
60 50 40 30 20
colored 10 0 300 500
750 1000 1250 1500 1750 2000 2250 2500 wavelength /nm
Fig. 3. Transmittance spectra of the Gesimat electrochromic device in fully bleached and colored states.
changes from 9% in the bleached state to 6% in the colored state and the solar reflectance from 8% (bleached) to 7% (colored). The switching is performed by application of DC voltages between about 0.5 and 2.5 V. In the polarity with WO3 at the negative terminal and Prussian Blue at the positive terminal, the device is colored, by changing the polarity the device is bleached. During switching, the color changes from colorless transparent to blue and vice versa. If the voltage is switched off during switching at any coloration state, the momentary coloration state stays unchanged (memory effect). Therefore, electrical energy is required only during switching, not for maintaining a constant coloration
ARTICLE IN PRESS A. Kraft et al. / Solar Energy Materials & Solar Cells 90 (2006) 469–476
473
40 35
reflectance /%
30 25 20 15 10 5 0 300 500
750 1000 1250 1500 1750 2000 2250 2500 wavelength /nm
Fig. 4. Reflectance spectra of the Gesimat electrochromic device in fully bleached and colored states: dashed line, colored state; solid line, bleached state.
150 coloration: 1.4 V
2
1
current density/µA/cm2
100 50 0 -50 -100 -150 -200
bleaching: -1.4 V
0
200
400
600 800 time/sec
1000
1200
Fig. 5. Current density versus time during switching of laminated electrochromic glass samples in two different sizes: (1) 10 cm 30 cm, contact distance 10 cm, (2) 30 cm 30 cm, contact distance 30 cm (three (sample 1) or two (sample 2) switching cycles with 71.4 V).
state. This is due to the battery-like behavior of the electrochromic device [20]. For one full coloring or bleaching step between the maximum and minimum light transmittance, the energy consumption is approximately 200 W s/m2. The switching time strongly depends on the size of the electrochromic glass or more exactly on the distance of the outer electrical contacts (see also Fig. 1). Fig. 5 shows the current density–time relationship of three coloring–bleaching cycles of two electrochromic glass samples of different dimensions. As can be seen from this figure, with increasing distance between the electrical contacts (in this case from 10 to 30 cm), the
ARTICLE IN PRESS 474
A. Kraft et al. / Solar Energy Materials & Solar Cells 90 (2006) 469–476
switching time also increases. However, the switching speed can be accelerated by the use of a newly developed advanced electronic control system. Fig. 5 also shows that bleaching is faster than coloring. This can also be seen from Figs. 6 and 7 which show the change of the transmittance spectra during coloring and bleaching. From Fig. 5, the high reversibility of the switching process is also obvious. Currently, several durability tests are performed with promising results [21]. The most severe tests are temperature cycle and simulated solar radiation tests. During these tests, the samples switch continuously between the bleached and colored states or are held permanently either in the bleached state or in the colored state and are at the same time subjected to changing temperature or to simulated solar radiation. The temperature stress performed consisted of one temperature cycle per day with temperature stages of +30, +80 and 25 1C, each for 4 h. For the simulated solar radiation tests, the samples were irradiated for up to 80 days by a special metal halide bulb which generates a spectrum with an irradiance of about 1000 W/m2, which is close to that of natural sunlight (AM 1.5) [21]. After 144 temperature cycles with up to 34,560 simultaneous bleaching/coloring cycles and also after 80 days (1,920 h) of simulated solar radiation with simultaneous up to 10,000 switching cycles, the changes in the dynamic electrical and optical properties of samples after both tests were below 10% compared to the properties before the tests [21]. Additionally, investigations on the heat transport inside the glazing and on thermal stresses which can be induced due to a partial shading of a colored electrochromic glazing during sunlight irradiation have been performed [22]. For the most effective use regarding energy consumption and glare protection of electrochromic glazing in architectural applications, the control strategy is very important. Recently, it has been found that a control strategy considering whether a room is in use or not can lead to large savings of the energy needed for space cooling
80 70 transmittance /%
60
0s
50 40 30 30 s
20 10 300 s 0 300 500
60 s
750 1000 1250 1500 1750 2000 2250 2500 wavelength /nm
Fig. 6. Change of the transmittance spectra during coloring with 1.4 V. Eleven transmission spectra recorded at intervals of 30 s switching time between 0 and 300 s.
ARTICLE IN PRESS A. Kraft et al. / Solar Energy Materials & Solar Cells 90 (2006) 469–476
475
80 70 transmittance /%
60
180 s
50 40 30 20
120 s 0s
10 0 300 500
750 1000 1250 1500 1750 2000 2250 2500 wavelength /nm
Fig. 7. Change of the transmittance spectra during bleaching with 1.4 V. Seven transmission spectra recorded at intervals of 30 s switching time between 0 and 180 s.
[23,24]. The importance of the control strategy is also the result from tests with the new Gesimat electrochromic glazings [21,25]. For these tests the electrochromic glass was installed in a south-facing test facade. The experiments in this facade included energy saving and illuminance measurements at a desk at a distance of 1.5 m from the window.
4. Conclusions Since 1998, Gesimat is working on the development of a new laminated electrochromic glazing with the development focus on using low-cost technologies and/or state-of-the-art processes and materials of the glass-processing industry. The resulting new device and fabrication concept for an electrochromic window presented in this paper offers the possibility for a cost-effective production of large-area electrochromic glazing with high contrast ratio and long-term stability in the near future. Possible application areas include but are not limited to architectural and automotive smart glazings.
Acknowledgments We thank H. Stenzel (HT Troplast Troisdorf, Germany), M. Steuer and B. Papenfuhs (KSE GmbH Frankfurt/M., Germany) and T. Ha¨usler and U. Fischer (Department of Applied Physics, Brandenburg University of Technology Cottbus, Germany) for their collaboration during the development process. Part of this work was funded by the German Federal Ministry of Economics and Labour, Contract no. 0327233F.
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476
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[22] [23] [24] [25]
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