Complementary Electrochromic Devices Based on PANI or PANI/SiO2 and PMeT or PProDOT-Et2：Optimization and Stability
Date Issued
2009
Date
2009
Author(s)
Chen, Wei-Kai
Abstract
Recently, organic conducting polymers have gained increasingly attention for electrochromic (EC) applications, such as smart windows for energy saving, anti-glare mirrors for driving safety, displays and so on. Especially in this era of green energy, the complementary electrochromic devices (ECDs) based on organic thin films, possessing high coloration efficiency and memory effect, has the function of energy saving permanently upon the application of low power. In this study, four EC materials, polyaniline (PANI), PANI/silica (SiO2), poly(3-methylthiophene) (PMeT) and diethyl substituted poly(3,4-propylenedioxythiophene) (PProDOT-Et2) were used to construct four ECDs, in which PANI and PANI/SiO2 served as the anodically coloring materials, PMeT served as the anodically and cathodically coloring material and PProDOT-Et2 served as the cathodically coloring material. In the meantime, the optimization and the stability of these EC films and the assembled ECDs were also discussed toward getting an ECD with excellent performance.or PANI and PANI/SiO2 thin films, PANI/SiO2 composite films have been potentiaostatically prepared by an in-situ electrodeposition method in the presence of different contents of SiO2 nanoparticles and its electrochromic properties were studied. A PANI thin film was also prepared for comparison. When PANI was electrodeposited in the presence of SiO2 particles, the resulting PANI/SiO2 composite films possessed higher surface areas, larger redox charge capacities, and higher doping levels, and thus enhanced optical contrasts under the same coloration efficiency of PANI and PANI/SiO2 films. From the viewpoint of optical contrast, the optimal SiO2 content in 50 ml of the electrodeposition bath was 42 mg for electrodeposition. By incorporating SiO2 particles into the PANI film, the transmittance change at 700 nm from 10.7% to 16.4%, or an enhancement of ca. 50%, was achieved when operating between -0.5 and 0 V (vs. Ag/Ag+). The safe operating potential window was between -0.5 and 0.3 V (vs. Ag/Ag+). In addition, X-Ray photoelectron spectroscopy (XPS) study indicated that the presence of SiO2 might have retarded the formation of the highly oxidized PANI and hence improved the stability. Furthermore, the growth mechanism of the PANI/SiO2 composite film was proposed based on electrochemical quartz crystal microbalance (EQCM) technique. or the polythiophene (PT) derivatives, PMeT and PProDOT-Et2 thin films, both thin films were potentiostatically electrodeposited and their electrochromic properties were also studied. The safe operating potential window of PMeT thin films was between -0.4 and 0.6 V (vs. Ag/Ag+). The PMeT thin film showed red and blue by applying -0.4 and 0.6 V, respectively. The safe operating potential window of PProDOT-Et2 thin films was between -0.9 and 0.3 V (vs. Ag/Ag+). The PProDOT-Et2 thin film showed deep blue and light blue by applying -0.9 and 0.3 V, respectively.he stability of ECDs is of paramount importance for practical applications. In order to fabricate an ECD with good performance, the EC materials and the operating conditions for the ECD should be chosen carefully. Herein, four ECDs, PANI-PMeT, PANI/SiO2-PMeT, PANI-PProDOT-Et2 and PANI/SiO2-PProDOT-Et2, were assembled with the theoretical equations from the viewpoint of the safe operating potential window and the optical contrast of thin films for ECD design. Their electrochromic properties were also comparatively studied. Initial optimal results revealed that the PANI-PProDOT-Et2 and PANI/SiO2-PProDOT-Et2 ECDs showed better performance than that of the PANI-PMeT and PANI/SiO2-PMeT ECDs. Therefore, the PANI-PProDOT-Et2 and PANI/SiO2-PProDOT-Et2 ECDs were further optimized and their stability was comparatively discussed from the viewpoint of the charge capacity and the operating voltage of ECDs. Under suitable collocation, both ECDs showed light blue and deep blue by applying -0.8 and 0.9 V, respectively and possessed high optical contrast, coloration efficiency, ultrafast response and good open circuit (memory effect) and at-rest stabilities. In long-term cycling stability analysis at 25 ℃, the PANI-PProDOT-Et2 ECD showed obvious decay after 28,775 cycles. At 590 nm, the optical contrast of the PANI-PProDOT-Et2 ECD was ca. 58.1% at 1 cycle and ca. 30.2% at 45,000 cycles, whereas the optical contrast of the PANI/SiO2-PProDOT-Et2 ECD was ca. 56.5% at 1 cycle and ca. 50.0% at 45,000 cycles. In long-term cycling stability analysis at 70 ℃, the PANI-PProDOT-Et2 ECD showed obvious decay after 24,795 cycles. At 590 nm, the optical contrast of the PANI-PProDOT-Et2 ECD was ca. 58.5% at 1 cycle and ca. 3.0% at 53,000 cycles, whereas the optical contrast of the PANI/SiO2-PProDOT-Et2 ECD was ca. 59.9% at 1 cycle and ca. 43.0% at 53,000 cycles. Hence, the PANI/SiO2-PProDOT-Et2 ECD had good long-term cycling stability no matter at room or high temperature when compared to the PANI-PProDOT-Et2 ECD.n oder to improve the poor safety and the poor stability of ECDs caused by electrolyte leakage and sealing problems, the ECDs were sealed by surlyn and tried to use ionic liquid and gel electrolytes instead of the liquid electrolyte. Results revealed that electrolyte leakage and sealing problems could be improved by using surlyn. Nevertheless, that using ionic liquids instead of the liquid electrolyte is unsuitable for both PANI-PProDOT-Et2 and PANI/SiO2-PProDOT-Et2 ECDs. On the contrary, both ECDs using a gel electrolyte instead of the liquid electrolyte could enhance the at-rest stability and the long-term cycling stability at 25 ℃. The PANI-PProDOT-Et2 ECD showed obvious decay after 119,905 cycles. At 590 nm, the optical contrast of the PANI-PProDOT-Et2 ECD was ca. 55.3% at 1 cycle and ca. 0.3% at 200,205 cycles, whereas the optical contrast of the PANI/SiO2-PProDOT-Et2 ECD was ca. 52.4% at 1 cycle and ca. 39.7% at 200,235 cycles. Consequently, the PANI/SiO2-PProDOT-Et2 ECD had good long-term cycling stability at room temperature when compared to the PANI-PProDOT-Et2 ECD. But at high temperature, that using gel electrolyte instead of the liquid electrolyte will accelerate the decay of the PANI-PProDOT-Et2 and PANI/SiO2-PProDOT-Et2 ECDs.
Subjects
coloration efficiency
electrochromism
polyaniline (PANI)
PANI/silica (SiO2)
poly(3-methylthiophene) (PMeT)
stability
Type
thesis
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