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Polymeric electrolytes for WO3-based all solid-state electrochromic displays
Microelectronic Engineering 83 (2006) 1414–1417 www.elsevier.com/locate/mee
Polymeric electrolytes for WO3-based all solid-state electrochromic displays Maria Vasilopoulou, Ioannis Raptis, Panagiotis Argitis, Ioannis Aspiotis, Dimitris Davazoglou * Institute of Microelectronics, NCSR ‘‘Demokritos’’, Aghia Paraskevi 15310, Greece Available online 3 February 2006
Abstract All solid-state electrochromic displays were fabricated by chemically vapor depositing and patterning a tungsten oxide films on SnO2:F covered glass substrates and using solid or gel-like organic electrolytes. These ionically conductive and electronically insulating electrolytes were based on poly(methyl methacrylate) (PMMA) and poly(2-hydroxyethyl methacrylate) (PHEMA) into which phosphododecatungstic acid (H3PW12O40) was added at various concentrations. It was found that the degree of coloration does not depend on acid concentration. Also, displays using electrolytes with low PMMA content are very hard to bleach. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Electrochromic displays; Protonic polymeric or gel-like electrolytes
1. Introduction Electrochromic materials and devices have been studied for years because of its scientific and technological interest as smart windows displays and storage devices [1,2]. The property of electrochromism is found in a variety of organic [3,4] and inorganic materials [3] in bulk and film form. Among the inorganic electrochromic films the most studied is by far those of WO3. These films were deposited by vacuum evaporation [5,6], anodic oxidation of W sheets [7] and chemical vapor deposition (CVD) [8–10]. The electrochromism of WO3 thin film is always under interest, because of the numerous applications [11,12]. During the last two decades polymer electrolytes consisting of salts dissolved in polymers have been extensively studied [13–15] for potential applications such as lithium batteries, flexible electrochromic displays and smart windows [16,17]. Ionic conductivity in polymer electrolytes was believed to occur in a manner somewhat analogous
*
Corresponding author. Tel.: +30 210 6503117; fax: +30 210 6511723. E-mail address: [email protected] (D. Davazoglou).
0167-9317/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2006.01.046
to gas diffusion through polymer membranes. Segmental motion of the polymer chains continuously creates free volume into which the ions migrate and this process allows them to propagate along the electrolyte. In such a system the population of ions and electrons must be large in order to avoid problems with migration and ohmic resistance. A proton conductive polymeric electrolyte that would contain well-behaved electroactive centers is an interesting technological possibility in this context. In comparison to alkali metal electrolytes, proton conductors are characterized by higher dynamics of ionic transport. Several studies of proton-conducting polymer gels prepared using polyacrylates or polymethacrylates have been reported [18–22]. In most cases the applicable gel electrolyte is a two- or three-component system not only composed of a polymer matrix swollen with a solution of proton donor in a polar solvent but also containing redox sites. In the present work, we consider a H3PW12O40-doped methacrylate-based, one-component polymeric electrolyte, where phosphotungstic acid acts as proton donor. The electrochromic performance of displays based on chemically vapor deposited (CVD) WO3 films, using liquid and solid polymeric electrolytes are discussed.
M. Vasilopoulou et al. / Microelectronic Engineering 83 (2006) 1414–1417
1415
2. Fabrication of WO3 based patterned electrochromic devices
some of the former solutions at ratios from 1:1 to 8:1 of the polymer mass.
For the fabrication of electrochromic devices, W 100 nm thick films were deposited on commercially available SnO2:F covered glass substrates. These films were subsequently patterned and oxidized to WO3 (Scheme 1). Depositions were carried out in a horizontal, radiatively heated CVD reactor at low pressure (0.1 Torr) at 400 °C, from decomposition of W(CO)6 vapors [23]. After deposition the W films were patterned with AZ 5214TM photoresist using various photomasks, and etched. For the chemical etching of tungsten we have chosen aqueous solutions containing tetra-methyl ammonium hydroxide (TMAH) at amounts 5:1 per volume, which is compatible with Si technology and also gave at room temperature an etching rate of the order of 20 nm/min, so the etching time were about 5 min for each W film. Oxidations of the patterned films were made in a horizontal furnace at temperatures varying between 550 and 650 °C and at various times dependent on film thickness. After oxidation of the W film to WO3 electrochromic devices were formed using as counter electrode either another SnO2:F covered glass substrate or Al films evaporated through a shadow mask (300 nm thick). PMMA and/or PHEMA based polymeric films were used as electrolytes and ionic conductors. The PMMA polymer used is Elvacite 2041 purchased from DuPont and solutions in Methyl Iso Butyl Ketone (7–8% w/w) were prepared with heating up to 60 °C. Poly (2-hydroxy ethyl methacrylate, PHEMA) was purchased from Aldrich Co and solutions of PHEMA in ethyl(s)lactate (8–10% w/w) were prepared. Phosphotungstic acid hydrate (H3PW12O40) was added as proton generator in
3. Characterization of the EC displays In Fig. 1 the reflection spectra are shown for WO3-based EC displays using as electrolytes PMMA solutions 8% in MIBK containing phosphotungstic acid at concentrations 1:1 (a) and 1:8 (b) polymer:acid, using mass ratios. Al was used as counter electrode. Electrolytes were spun at 2000 rpm on the patterned WO3 film followed by curing at 80 °C for 2 min. Displays were colored at various degrees with various voltages. For each measurement a DC voltage was applied, which was remaining throughout the duration of the measurement (about 2 min). It can be observed that the reflection of the displays is decreasing gradually and reversibly to the half of the initial value with a voltage of 6 V. Moreover, it is seen that the degree of 70
0V +6 V +12 V -6 V -12 V
REFLECTIVITY, %
60
50
40
30
20
10
0 200
AZ resist W SnO2 on glass
1. LPCVD of 100 nm thick W film and spin coating of AZ positive tone resist
4. Resist’s stripping
500
600
700
800
700
800
70
0V +6 V +12 V -6 V -12 V
50
REFLECTIVITY, %
3. Wet etching of W
400
WAVELENGTH, NM
60
2. Exposure and development of resist
300
40
30
20
10
0 200
300
400
500
600
WAVELENGTH, NM 5. Oxidation of W to WO3 Scheme 1. Fabrication steps of the electrochromic device.
Fig. 1. Reflectance spectra of displays using as electrolytes PMMA solutions 8% in MIBK containing H3PW12O40 at mass concentrations 1:1 (up) and 1 part polymer:8 parts acid (down).
M. Vasilopoulou et al. / Microelectronic Engineering 83 (2006) 1414–1417
coloration does not depend strongly on the concentration of acid. It must be pointed out that for displays using such electrolytes coloration and bleaching times were comparable and equal to approximately 500 ms. This is contrary to what has been observed for EC displays using liquid electrolytes and may be explained assuming that after insertion of the protons generated from the acid decomposition in the electrolyte film into the WO3, the last remains charged. This creates an internal electric field, which superimposes to the bleaching voltage facilitating this bleaching process. When the concentration of PMMA in the solution decreases the thickness of the electrolyte film also decreases. As shown in Fig. 2 the EC displays using electrolytes containing 4% PMMA need higher voltages to color at the same degree as those using electrolytes containing PMMA at a concentration of 8% and having similar acid concentrations. The thicknesses of the electrolyte films were 1 and 0.5 lm, respectively. Displays using electrolytes with low PMMA content are very hard to bleach. This result is somehow curious since thinner films means that 70
0V +6 V +12 V -6 V -12 V
60
REFLECTIVITY, %
50
higher voltages are applied on the mobile ions so the coloration and the bleaching, which are associated with the insertion and the extraction of these ions in and out of the WO3 film respectively, should have to be facilitated. The phenomenon does not seem to be related to the lack of mobile ions in the thinner films since coloration occurs, therefore it is rather related to the ionic mobility. Indeed, thinner PMMA films are easier to solidify at the curing temperature of 80 °C than thicker ones and this solidification implies a decrease of the mobility of ions. In Fig. 3(a) reflectance spectra taken on an EC display using gel-like electrolyte, i.e., not cured after spinning consisting of PHEMA 2% in ethyl-lactate containing phosphotungstic acid at a concentration 1:2, colored and bleached
60 0V
50
REFLECTIVITY, %
1416
40
+ 6V
30
+ 12 V
20 -6V
40
10 30
-12V
0 300
20
400
500
600
700
800
900
WAVELENGTH, NM
10
0 200
300
400
500
600
700
800
60
WAVELENGTH, NM
0V +6 V +12 V -6 V -12 V
60
REFLECTIVITY, %
REFLECTIVITY, %
70
50
40
50
new: 0 V
40
new:+ 15 V
30
old (24 hours of operation): 0 V
20
old: + 15 V
30
10 20
0
10
300
400
500
600
700
800
900
WAVELENGTH, NM
0 200
300
400
500
600
700
800
W AVELENGTH, NM
Fig. 2. Reflectance spectra of EC displays using as electrolytes films of PMMA 4% in MIBK (up) and 8% (down), containing H3PW12O40 at a mass concentration of 1 part polymer:4 parts acid.
Fig. 3. (a) Reflectance spectra recorded on an EC display using gel-like electrolyte (not heated after spinning) composed of PHEMA added phospho-dodecatungstic acid (1 part polymer:2 parts acid) 0.25 lm thick (up), (b) On a display using gel-like electrolyte composed with PMMA 4% added phospho-dodecatungstic acid at a concentration of 1:2 (down).
M. Vasilopoulou et al. / Microelectronic Engineering 83 (2006) 1414–1417
1417
presented. A second SnO2 substrate was used as counter electrode. 4. Conclusions Electrochromic devices based on WO3 LPCVD films have been fabricated using lithographic and etching techniques standard in Si technology. These devices were using polymeric electrolytes base on PMMA and PHEMA into which phospho-dodecatungstic acid was added at various concentrations. It was found that the degree of coloration does not depend on the concentration of acid, which means that the produced ions are enough to color the WO3 film even at low acid concentrations. Coloration and bleaching times are similar indicating that the lack of ions from the electrolyte causes the creation of an internal field, which attracts back in the electrolyte the ions inserted into the WO3 film. Also, displays using electrolytes with low PMMA content are very hard to bleach due to the solidification of the film, which causes a decrease of the ionic mobility. References
Fig. 4. An electrochromic display using a polymeric electrolyte consisting of PMMA film containing phospho-dodecatungstic acid at mass ratio 1:1, in two different states of coloration. A second SnO2:F substrate was used as counter electrode.
with various voltages are shown. It can be seen that the voltages involved are higher than those used for PMMAbased displays. The thin electrolyte film was solidified and this is a possible explanation for the high voltages needed for the coloration of this display. Another possible explanation is that protons produced by the acid, the incorporation of which into the WO3 causes the coloration, are now captured by the hydroxyl ions of the PHEMA. In Fig. 3(b) reflection spectra taken at the fully colored and bleached states on a display in the beginning of its operation and after 24 h of operation are shown. In this case the gel-like electrolyte was composed with PMMA 4% added phosphotungstic acid at a concentration of 1:2. It can be seen that the curves do not entirely coincide and this is probably due to protons that remain into the WO3 film after every coloration-bleaching cycle. However, in agreement with results taken on displays using liquid electrolytes, the long-time use renders displays faster. In Fig. 4 a WO3-based (patterned ‘‘Athens Olympics 2004’’) electrochromic display using a polymeric electrolyte consisting of PMMA 8% film containing phosphotungstic acid hydrate at ratio 1:1, in various states of coloration is
[1] B.C. Thomson, P. Schottland, K. Zong, J.R. Reynolds, Chem. Mater. 12 (2000) 1563. [2] D.R. Rosseinsky, R.J. Mortimer, Adv. Mater. 13 (2001) 783. [3] C. Lampert, Sol. Energ. Mater. 11 (1984) 828. [4] W. Dautremont-Smith, Displays 3 (1982) 3. [5] T. Kamimori, J. Nagai, M. Mizuhashi, Proc. SPIE 428 (1982) 51. [6] O. Bohnke, C. Bohnke, G. Robert, B. Carcuille, Solid State Ionics 6 (1982) 121. [7] A. DiPaola, F. DiQuarto, C. Sunseri, J. Electrochem. Soc. 125 (1987) 1344. [8] A. Donnadieu, D. Davazoglou, Proc. SPIE (1987) 65636. [9] D. Davazoglou, A. Donnadieu, O. Bohnke, Sol. Energ. Mater. 16 (1987) 55. [10] O. Bohnke, C. Bohnke, A. Donnadieu, D. Davazoglou, J. Appl. Electrochem. 18 (1988) 447. [11] L.J. LeGore, R.J. Lad, S.C. Moulzolf, J.F. Vetelino, B.G. Frederick, E.A. Kenik, Thin Solid Films 406 (2002) 79. [12] S. Yu, N. Kumagai, Z.L. Liu, J.Y. Lee, J. Solid State Electrochem. 2 (1998) 394. [13] M. Armand, Adv. Mater. 2 (6–7) (1990) 278. [14] D.R. MacFarlane, J.H. Huang, M. Forsyth, Nature 402 (1999) 792. [15] Z. Gadjourova, D. Martin y Marero, K.H. Andersen, Y.G. Andeev, P.G. Bruce, Chem. Mater. 13 (2001) 1282. [16] J.-M. Tarascon, M. Armand, Nature 414 (2001) 359. [17] M. Christie, S.J. Lilley, E. Staunton, Y.G. Andreev, P.G. Bruce, Nature 433 (2005) 50. [18] D. Kreurer, Chem. Mater. 8 (1996) 610. [19] D. Raducha, W. Wieczorek, Z. Florjanczyk, J.R. Stevens, J. Phys. Chem. 100 (1996) 20126. [20] P. Pissis, A. Kyritsis, Solid State Ionics 97 (1997) 105. [21] A.M. Grillone, S. Panero, B.A. Retamal, B. Scrosati, J. Electrochem. Soc. 146 (1999) 27. [22] A. Lewera, G. Zukowska, K. Miecznikowski, M. Chojak, W. Wieczorek, P.J. Kulesza, Anal. Chim. Acta 536 (1–2) (2005) 275. [23] D. Davazoglou, G. Pallis, B. Psicharis, S. Logothetidis, M. Gioti, J. Appl. Phys. 77 (1995) 6070.
Polymeric electrolytes for WO3-based all solid-state electrochromic displays Maria Vasilopoulou, Ioannis Raptis, Panagiotis Argitis, Ioannis Aspiotis, Dimitris Davazoglou * Institute of Microelectronics, NCSR ‘‘Demokritos’’, Aghia Paraskevi 15310, Greece Available online 3 February 2006
Abstract All solid-state electrochromic displays were fabricated by chemically vapor depositing and patterning a tungsten oxide films on SnO2:F covered glass substrates and using solid or gel-like organic electrolytes. These ionically conductive and electronically insulating electrolytes were based on poly(methyl methacrylate) (PMMA) and poly(2-hydroxyethyl methacrylate) (PHEMA) into which phosphododecatungstic acid (H3PW12O40) was added at various concentrations. It was found that the degree of coloration does not depend on acid concentration. Also, displays using electrolytes with low PMMA content are very hard to bleach. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Electrochromic displays; Protonic polymeric or gel-like electrolytes
1. Introduction Electrochromic materials and devices have been studied for years because of its scientific and technological interest as smart windows displays and storage devices [1,2]. The property of electrochromism is found in a variety of organic [3,4] and inorganic materials [3] in bulk and film form. Among the inorganic electrochromic films the most studied is by far those of WO3. These films were deposited by vacuum evaporation [5,6], anodic oxidation of W sheets [7] and chemical vapor deposition (CVD) [8–10]. The electrochromism of WO3 thin film is always under interest, because of the numerous applications [11,12]. During the last two decades polymer electrolytes consisting of salts dissolved in polymers have been extensively studied [13–15] for potential applications such as lithium batteries, flexible electrochromic displays and smart windows [16,17]. Ionic conductivity in polymer electrolytes was believed to occur in a manner somewhat analogous
*
Corresponding author. Tel.: +30 210 6503117; fax: +30 210 6511723. E-mail address: [email protected] (D. Davazoglou).
0167-9317/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2006.01.046
to gas diffusion through polymer membranes. Segmental motion of the polymer chains continuously creates free volume into which the ions migrate and this process allows them to propagate along the electrolyte. In such a system the population of ions and electrons must be large in order to avoid problems with migration and ohmic resistance. A proton conductive polymeric electrolyte that would contain well-behaved electroactive centers is an interesting technological possibility in this context. In comparison to alkali metal electrolytes, proton conductors are characterized by higher dynamics of ionic transport. Several studies of proton-conducting polymer gels prepared using polyacrylates or polymethacrylates have been reported [18–22]. In most cases the applicable gel electrolyte is a two- or three-component system not only composed of a polymer matrix swollen with a solution of proton donor in a polar solvent but also containing redox sites. In the present work, we consider a H3PW12O40-doped methacrylate-based, one-component polymeric electrolyte, where phosphotungstic acid acts as proton donor. The electrochromic performance of displays based on chemically vapor deposited (CVD) WO3 films, using liquid and solid polymeric electrolytes are discussed.
M. Vasilopoulou et al. / Microelectronic Engineering 83 (2006) 1414–1417
1415
2. Fabrication of WO3 based patterned electrochromic devices
some of the former solutions at ratios from 1:1 to 8:1 of the polymer mass.
For the fabrication of electrochromic devices, W 100 nm thick films were deposited on commercially available SnO2:F covered glass substrates. These films were subsequently patterned and oxidized to WO3 (Scheme 1). Depositions were carried out in a horizontal, radiatively heated CVD reactor at low pressure (0.1 Torr) at 400 °C, from decomposition of W(CO)6 vapors [23]. After deposition the W films were patterned with AZ 5214TM photoresist using various photomasks, and etched. For the chemical etching of tungsten we have chosen aqueous solutions containing tetra-methyl ammonium hydroxide (TMAH) at amounts 5:1 per volume, which is compatible with Si technology and also gave at room temperature an etching rate of the order of 20 nm/min, so the etching time were about 5 min for each W film. Oxidations of the patterned films were made in a horizontal furnace at temperatures varying between 550 and 650 °C and at various times dependent on film thickness. After oxidation of the W film to WO3 electrochromic devices were formed using as counter electrode either another SnO2:F covered glass substrate or Al films evaporated through a shadow mask (300 nm thick). PMMA and/or PHEMA based polymeric films were used as electrolytes and ionic conductors. The PMMA polymer used is Elvacite 2041 purchased from DuPont and solutions in Methyl Iso Butyl Ketone (7–8% w/w) were prepared with heating up to 60 °C. Poly (2-hydroxy ethyl methacrylate, PHEMA) was purchased from Aldrich Co and solutions of PHEMA in ethyl(s)lactate (8–10% w/w) were prepared. Phosphotungstic acid hydrate (H3PW12O40) was added as proton generator in
3. Characterization of the EC displays In Fig. 1 the reflection spectra are shown for WO3-based EC displays using as electrolytes PMMA solutions 8% in MIBK containing phosphotungstic acid at concentrations 1:1 (a) and 1:8 (b) polymer:acid, using mass ratios. Al was used as counter electrode. Electrolytes were spun at 2000 rpm on the patterned WO3 film followed by curing at 80 °C for 2 min. Displays were colored at various degrees with various voltages. For each measurement a DC voltage was applied, which was remaining throughout the duration of the measurement (about 2 min). It can be observed that the reflection of the displays is decreasing gradually and reversibly to the half of the initial value with a voltage of 6 V. Moreover, it is seen that the degree of 70
0V +6 V +12 V -6 V -12 V
REFLECTIVITY, %
60
50
40
30
20
10
0 200
AZ resist W SnO2 on glass
1. LPCVD of 100 nm thick W film and spin coating of AZ positive tone resist
4. Resist’s stripping
500
600
700
800
700
800
70
0V +6 V +12 V -6 V -12 V
50
REFLECTIVITY, %
3. Wet etching of W
400
WAVELENGTH, NM
60
2. Exposure and development of resist
300
40
30
20
10
0 200
300
400
500
600
WAVELENGTH, NM 5. Oxidation of W to WO3 Scheme 1. Fabrication steps of the electrochromic device.
Fig. 1. Reflectance spectra of displays using as electrolytes PMMA solutions 8% in MIBK containing H3PW12O40 at mass concentrations 1:1 (up) and 1 part polymer:8 parts acid (down).
M. Vasilopoulou et al. / Microelectronic Engineering 83 (2006) 1414–1417
coloration does not depend strongly on the concentration of acid. It must be pointed out that for displays using such electrolytes coloration and bleaching times were comparable and equal to approximately 500 ms. This is contrary to what has been observed for EC displays using liquid electrolytes and may be explained assuming that after insertion of the protons generated from the acid decomposition in the electrolyte film into the WO3, the last remains charged. This creates an internal electric field, which superimposes to the bleaching voltage facilitating this bleaching process. When the concentration of PMMA in the solution decreases the thickness of the electrolyte film also decreases. As shown in Fig. 2 the EC displays using electrolytes containing 4% PMMA need higher voltages to color at the same degree as those using electrolytes containing PMMA at a concentration of 8% and having similar acid concentrations. The thicknesses of the electrolyte films were 1 and 0.5 lm, respectively. Displays using electrolytes with low PMMA content are very hard to bleach. This result is somehow curious since thinner films means that 70
0V +6 V +12 V -6 V -12 V
60
REFLECTIVITY, %
50
higher voltages are applied on the mobile ions so the coloration and the bleaching, which are associated with the insertion and the extraction of these ions in and out of the WO3 film respectively, should have to be facilitated. The phenomenon does not seem to be related to the lack of mobile ions in the thinner films since coloration occurs, therefore it is rather related to the ionic mobility. Indeed, thinner PMMA films are easier to solidify at the curing temperature of 80 °C than thicker ones and this solidification implies a decrease of the mobility of ions. In Fig. 3(a) reflectance spectra taken on an EC display using gel-like electrolyte, i.e., not cured after spinning consisting of PHEMA 2% in ethyl-lactate containing phosphotungstic acid at a concentration 1:2, colored and bleached
60 0V
50
REFLECTIVITY, %
1416
40
+ 6V
30
+ 12 V
20 -6V
40
10 30
-12V
0 300
20
400
500
600
700
800
900
WAVELENGTH, NM
10
0 200
300
400
500
600
700
800
60
WAVELENGTH, NM
0V +6 V +12 V -6 V -12 V
60
REFLECTIVITY, %
REFLECTIVITY, %
70
50
40
50
new: 0 V
40
new:+ 15 V
30
old (24 hours of operation): 0 V
20
old: + 15 V
30
10 20
0
10
300
400
500
600
700
800
900
WAVELENGTH, NM
0 200
300
400
500
600
700
800
W AVELENGTH, NM
Fig. 2. Reflectance spectra of EC displays using as electrolytes films of PMMA 4% in MIBK (up) and 8% (down), containing H3PW12O40 at a mass concentration of 1 part polymer:4 parts acid.
Fig. 3. (a) Reflectance spectra recorded on an EC display using gel-like electrolyte (not heated after spinning) composed of PHEMA added phospho-dodecatungstic acid (1 part polymer:2 parts acid) 0.25 lm thick (up), (b) On a display using gel-like electrolyte composed with PMMA 4% added phospho-dodecatungstic acid at a concentration of 1:2 (down).
M. Vasilopoulou et al. / Microelectronic Engineering 83 (2006) 1414–1417
1417
presented. A second SnO2 substrate was used as counter electrode. 4. Conclusions Electrochromic devices based on WO3 LPCVD films have been fabricated using lithographic and etching techniques standard in Si technology. These devices were using polymeric electrolytes base on PMMA and PHEMA into which phospho-dodecatungstic acid was added at various concentrations. It was found that the degree of coloration does not depend on the concentration of acid, which means that the produced ions are enough to color the WO3 film even at low acid concentrations. Coloration and bleaching times are similar indicating that the lack of ions from the electrolyte causes the creation of an internal field, which attracts back in the electrolyte the ions inserted into the WO3 film. Also, displays using electrolytes with low PMMA content are very hard to bleach due to the solidification of the film, which causes a decrease of the ionic mobility. References
Fig. 4. An electrochromic display using a polymeric electrolyte consisting of PMMA film containing phospho-dodecatungstic acid at mass ratio 1:1, in two different states of coloration. A second SnO2:F substrate was used as counter electrode.
with various voltages are shown. It can be seen that the voltages involved are higher than those used for PMMAbased displays. The thin electrolyte film was solidified and this is a possible explanation for the high voltages needed for the coloration of this display. Another possible explanation is that protons produced by the acid, the incorporation of which into the WO3 causes the coloration, are now captured by the hydroxyl ions of the PHEMA. In Fig. 3(b) reflection spectra taken at the fully colored and bleached states on a display in the beginning of its operation and after 24 h of operation are shown. In this case the gel-like electrolyte was composed with PMMA 4% added phosphotungstic acid at a concentration of 1:2. It can be seen that the curves do not entirely coincide and this is probably due to protons that remain into the WO3 film after every coloration-bleaching cycle. However, in agreement with results taken on displays using liquid electrolytes, the long-time use renders displays faster. In Fig. 4 a WO3-based (patterned ‘‘Athens Olympics 2004’’) electrochromic display using a polymeric electrolyte consisting of PMMA 8% film containing phosphotungstic acid hydrate at ratio 1:1, in various states of coloration is
[1] B.C. Thomson, P. Schottland, K. Zong, J.R. Reynolds, Chem. Mater. 12 (2000) 1563. [2] D.R. Rosseinsky, R.J. Mortimer, Adv. Mater. 13 (2001) 783. [3] C. Lampert, Sol. Energ. Mater. 11 (1984) 828. [4] W. Dautremont-Smith, Displays 3 (1982) 3. [5] T. Kamimori, J. Nagai, M. Mizuhashi, Proc. SPIE 428 (1982) 51. [6] O. Bohnke, C. Bohnke, G. Robert, B. Carcuille, Solid State Ionics 6 (1982) 121. [7] A. DiPaola, F. DiQuarto, C. Sunseri, J. Electrochem. Soc. 125 (1987) 1344. [8] A. Donnadieu, D. Davazoglou, Proc. SPIE (1987) 65636. [9] D. Davazoglou, A. Donnadieu, O. Bohnke, Sol. Energ. Mater. 16 (1987) 55. [10] O. Bohnke, C. Bohnke, A. Donnadieu, D. Davazoglou, J. Appl. Electrochem. 18 (1988) 447. [11] L.J. LeGore, R.J. Lad, S.C. Moulzolf, J.F. Vetelino, B.G. Frederick, E.A. Kenik, Thin Solid Films 406 (2002) 79. [12] S. Yu, N. Kumagai, Z.L. Liu, J.Y. Lee, J. Solid State Electrochem. 2 (1998) 394. [13] M. Armand, Adv. Mater. 2 (6–7) (1990) 278. [14] D.R. MacFarlane, J.H. Huang, M. Forsyth, Nature 402 (1999) 792. [15] Z. Gadjourova, D. Martin y Marero, K.H. Andersen, Y.G. Andeev, P.G. Bruce, Chem. Mater. 13 (2001) 1282. [16] J.-M. Tarascon, M. Armand, Nature 414 (2001) 359. [17] M. Christie, S.J. Lilley, E. Staunton, Y.G. Andreev, P.G. Bruce, Nature 433 (2005) 50. [18] D. Kreurer, Chem. Mater. 8 (1996) 610. [19] D. Raducha, W. Wieczorek, Z. Florjanczyk, J.R. Stevens, J. Phys. Chem. 100 (1996) 20126. [20] P. Pissis, A. Kyritsis, Solid State Ionics 97 (1997) 105. [21] A.M. Grillone, S. Panero, B.A. Retamal, B. Scrosati, J. Electrochem. Soc. 146 (1999) 27. [22] A. Lewera, G. Zukowska, K. Miecznikowski, M. Chojak, W. Wieczorek, P.J. Kulesza, Anal. Chim. Acta 536 (1–2) (2005) 275. [23] D. Davazoglou, G. Pallis, B. Psicharis, S. Logothetidis, M. Gioti, J. Appl. Phys. 77 (1995) 6070.