The Study of Prussian Blue, Conducting Polymer PEDOT and Their Assembled Electrochromic Devices： Thermal and Long-term Stabilities, and the Behavior of Ion Transport within PEDOT Thin Films
Date Issued
2006
Date
2006
Author(s)
Liao, Chun-Hao
DOI
zh-TW
Abstract
In this work, the complementary electrochromic device (ECD) with a color change between nearly transparent light blue and deep blue was assembled by poly(3,4-alkylenedioxythiophene) (PEDOT) and Prussian blue (PB). For the preparation of the electrolyte, the solvent was propylene carbonate (PC) and the salt was LiClO4 or TBAClO4. The objective of this study is focused on the stabilities of PB and PEDOT thin films as well as the PEDOT-PB ECDs at R.T. and 70℃. The ion transport within the PEDOT and PB are also discussed. Furthermore, the potential distributions of PEDOT and PB within the ECDs were measured to explain the change of the transmittance responses in the ECDs with increasing cycle number.
After evaluating thermal stabilities of the PEDOT and PB thin films in 0.1 M LiClO4/PC solution at 70℃, the results showed that both PEDOT and PB thin films had good at-rest thermal stabilities but worse cycling thermal stabilities than their at-rest thermal stabilities. Moreover, we proposed that when a PB thin film is switched from the PB state to the Prussian White (PW) state in 0.1 M LiClO4/PC solution, Li+ will be inserted into the lattice and some will be trapped. This phenomenon forbids some of the PW oxidizing to the PB state and causes the decay of the darkened transmittance with increasing cycle number. The EQCM analysis revealed that the electroneutrality of the PEDOT thin film was mantained by the transports of both cation and anion when PEDOT was cycled between its neutral state and p-type doping state. In LiClO4/PC solution, the charge compensation within the PEDOT thin film is dominated by Li+. However, in TBAClO4/PC solution, dominant ion for charge compensation is ClO4-. Furthermore, we proposed an equation to explain the redox process for PEDOT and calculated the corresponding stoichiomtric numbers.
From the thermal stability test of PEDOT-PB ECD at 70℃, the results showed that the ECDs had good at-rest thermal stabilities but their cycling thermal stabilities were obviously worse than their at-rest thermal stability. The results revealed that 70℃ would accelerate the cycling instabilities of the ECDs. On the other hand, whether the ECDs were switched at R.T. or 70℃, applying -1.2 V for darkening and 0.6 V for bleaching could achieve better cycling stabilities and larger transmittance differences. When the ECD was cycled potentiostatically between -1.2 and 0.6 V for 10,000 cycles at R.T., the transmittance difference still remained 95.8% of the maximum value (ΔTMax). When cycled at 70℃, its remaining transmittance difference at 10,000th cycle decreased to 61.0% of ΔTMax. Finally, according to the potential distributions of PEDOT and PB thin films within the ECDs, we can explain the changes of the transmittance responses of the ECDs as a function of cycle number and also the reason why the cycling instabilities of the ECDs being accelerated at 70℃.
Subjects
電致色變元件
EQCM
poly(3,4-alkylenedioxythiophene) (PEDOT)
普魯士藍
熱穩定性
電位分佈
Electrochromic device
Prussian blue (PB)
thermal stability
potential distribution
Type
thesis
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