On the Optimization and Long-term Stability of the Electrochromic Devices Assembling with Conducting Polymers PEDOT or Its Derivative and Prussian Blue
Date Issued
2004
Date
2004
Author(s)
TUNG, TSAI-SHIH
DOI
zh-TW
Abstract
In this thesis, the fundamental properties and the applications of the electrochromic technologies are investigated. Electrochromism is a reversible phenomenon that some materials change their optical absorbance and exhibit visible color change in response to a dc voltage or current source. In this study, a new complementary electrochromic system, which comprises conducting polymers, ploy(3,4-ethylenedioxythiophene) (PEDOT) or its derivative (poly(3,3-dimethyl-3,4-dihydro-2H-thieno [3,4-b][1,4]dioxepine) (PProDOT-Me2), and an inorganic material, Prussian blue (PB), is developed for the first time.
In experiments, the conducting polymer, PEDOT (or PProDOT-Me2), was electropolymerized onto the conducting glass (indium tin oxide, ITO) by a potentiostatic method with an applied potential of 1.2V (vs. Ag/Ag+); PB was cathodically deposited onto ITO by applying a constant current density of -20 μA/cm2. Subsequently, the electrochromic thin films were characterized by the cyclic voltammetry, UV-visible spectrophotometry, and electrochemical quartz crystal microbalance. In a 1.0 M LiClO4/PC solution, PB was reduced to colorless at -0.9V (vs. Ag/Ag+) and oxidized to blue at 0.4V (vs. Ag/Ag+) based on reversible redox reactions. On the other hand, PEDOT displayed deep blue at -1.2V (vs. Ag/Ag+) by the dedoping of the anions (ClO4-). With the increase of the applied potential in the positive direction, PEDOT changed to light blue (0.3V vs. Ag/Ag+). The transmittance difference (ΔT) of the PEDOT at 590 nm is 56.4%. Furthermore, PProDOT-Me2 can provide a deep violet-blue reduced state at -0.8V (vs. Ag/Ag+) and a transparent oxidized state at 0.4V (vs. Ag/Ag+), resulting in a ΔT of 68.4% at 578 nm.
Subsequently, PEDOT-PB devices were assembled to explore the optimal parameters on the performance of the devices. The devices exhibited deep blue and light blue at the colored state and bleached state, respectively. The safe operational coloring and bleaching voltages of the devices, obtained from the experiments, were -1.5V (PEDOT vs. PB) and 0.6V (PEDOT vs. PB), respectively. Under these voltages, one device was subjected to the cycling stability tests by a double potential step. After continuous 152,140 cycles, the ΔT still retained at 39%. On the matching of the charge density of the two electrodes, when the charge capacity ratio (R) was controlled close to 1, the device had a maximum transmittance difference. Additionally, after 100 days in the long-term at-rest stability tests, the ΔT of these devices (0.50<R<1.52) still retained above 50% when the R values were controlled between 0.79 and 1.15. The salt concentration, however, had no significant influence on the performance of the devices. After 140 days of the at-rest stability tests, the decays on the ΔT of the devices were less than 10%. The above results show that after choosing the optimal parameters, the cycling stabilities and the long-term at-rest stabilities of the PEDOT-PB devices are better than those of PEDOT-based electrochromic devices reported in literature.
When the above optimal parameters were applied to the PProDOT-Me2-PB devices, those devices achieved a better cell performance compared to the PEDOT-PB devices, including a ΔT of 60.1% (11.0%-71.1%) at 578 nm and a coloration efficiency larger than 450 cm2/C. Besides, a PProDOT-Me2-PB device, with a coloring voltage of -1.2V (PProDOT-Me2 vs. PB) and a bleaching voltage of 0.6V (PProDOT-Me2 vs. PB), retained a ΔT value of 54.7% (ΔTmax = 57.6%) after continuous 342,250 operational cycles. Moreover, another device retained a ΔT value of 57.2% (ΔTmax = 59.9%) after 140 days in the at-rest operation. The above results show that the PProDOT-Me2-PB devices perform better in terms of stabilities.
The experimental results in this research provide an operational, technological platform, on a laboratory level, for the development of the electrochromic devices, the optimization on the optical performances of the devices, and the improvement of the long-term stability of the devices. Furthermore, the PEDOT-PB devices and PProDOT-Me2-PB devices were successfully proved to have the potentials to compete with the commercial devices.
Subjects
著色效率
電致色變元件
穩定性
普魯士藍
poly(3,4-alkylenedioxythiophenes) (PXDOT:包含PEDOT和PProDOT-Me2)
Prussian blue (PB)
stability
coloration efficiency
electrochromic device
poly(3,4-alkylenedioxythiophenes) (PXDOT: PEDOT and PProDOT-Me2)
Type
thesis
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