以PEDOT-Cl或PProDOT-Et2與InHCF構成之互補式電致色變元件

Abstract

In this work, the complementary electrochromic devices (ECDs) were assembled by using modified conducting polymer (PEDOT-Cl) or its derivative (PProDOT-Et2) and a water-soluble Prussian blue analog, indium hexacyanoferrate (InHCF). For a liquid electrolyte-based ECD, leakage of electrolyte is a serious problem in the long-term stability test; therefore, we replaced the liquid electrolyte by PMMA gel electrolyte to improve its stability. Owing to the optical property of the PProDOT-Et2/InHCF ECD is better than that of the PEDOT-Cl/InHCF, the former system was studied using the PMMA gel electrolyte and investigated the stability of the ECD at room temperature (R.T.) and 50 oC. The main motivation to develop these two ECDs is that the optical density change of the counter electrode (InHCF) is small and the color change in the visible region is nearly transparent; therefore, all the optical density change was contributed from the cathodically coloring material. In this study, the electrochromic (EC) properties of thin films and devices were analyzed by cyclic voltammetry, potential step, and in-situ UV-Vis spectrophotometry. Two cathodically coloring materials were chosen in this study and will be discussed in Chapter 4. One was accidently obtained by adding chloride ions with strong nucleophilicity as the supporting electrolyte during electro-deposition of poly(3,4-ethylenedioxythiophene) (PEDOT), which is named PEDOT-Cl. This material exhibited light blue and red brown at the oxidized state and reduced state, respectively. Normally, the pristine PEDOT thin film can be switched between deep blue and light blue; however, the phenomenon we observed here is dramatically different from what have been reported in literatures. Since PEDOT-Cl has no transparent state in both the reduced state and the oxidized state, the obtained transmittance change of the film was only 30%. Therefore, we chose a high transmittance change conducting polymer, (poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]dioxepine), or PProDOT-Et2, thin film as the complementary cathodically coloring material in this study. Furthermore, electrochemical quartz crystal microbalance (EQCM) was used to observe the ionic transportation in a PEDOT-Cl thin film during the redox reactions and the results concluded that the PEDOT-Cl was an anion-dominant EC material, which is the same as that of the PEDOT. The analyses of anodically coloring indium hexacyanoferrate (InHCF) and its electrochemical properties will be discussed in Chapter 5. At first, we take the recipe from Kurihara’s group as reference to prepare the water-soluble InHCF nanoparticle ink. According to XRD analysis, the lattice of InHCF was found to be identical to what reported in the literature in which InHCF was synthesized by electro-deposition. In addition, the images of SEM show that the particle size is in nano scale. The EC properties of thin films were analyzed by cyclic voltammetry, potential step, and in-situ UV-Vis spectrophotometry. We focused on the EC performance of both PEDOT-Cl/InHCF ECD and PProDOT-Et2/InHCF ECD, with the maximum absorption wavelength at 500 and 590 nm, respectively, implying that the InHCF had little contribution to the device’s optical response. In the PEDOT-Cl/InHCF ECD, the transmittance change (∆T) was 23.3% under the potential bias of -0.1 ~ -1.4 V and the response times for coloring and bleaching was 2.7 and 2.5 s, respectively. Also the coloration efficiency can be calculated to be 570.7 cm2/C at 500 nm. In contrast, in the PProDOT-Et2/InHCF ECD, the ∆T was 44.7% under the operating potential bias of 0.5 ~ -0.9 V and the response times for coloring and bleaching was 1.6 and 1.8 s, respectively. The coloration efficiency was calculated to be 941.5 cm2/C at 590 nm. By comparing these two ECDs, we found that the PProDOT-Et2/InHCF ECD possessed better EC properties, including larger optical contrast, faster response times and higher coloration efficiency. We further investigated the temperature effect and its long-term stability by using PMMA gel electrolyte. For the case of liquid electrolyte and switching at R.T., the ∆T still remained 89% of its original value after 10,000 continuous cyclings, namely, the ∆T value decreased from 41.3% to 36.7%. For the case of liquid electrolyte and switching at 50 oC, the ∆T value decreased from 39.1% to 32.8% and only remained 84% of its original value for 10,000 continuous cyclings. For the case of gel electrolyte and switching at 50 oC, the ∆T also remained 89% of its original value after 10,000 continuous cyclings. That is, the ∆T value decreased from 51.9% to 46.0%, implying that the PMMA gel electrolyte not only can solve the problem of electrolyte leakage but also can improve the optical performance of the ECD.