互補式電致色變元件PANI-PEDOT光譜電化學與最適化之研究

Abstract

本研究論文採用氧化著色的導電高分子polyaniline (PANI)搭配還原著色的新型導電高分子poly(3,4-ethylenedioxythiophene) (PEDOT)組裝一互補式電致色變元件。研究首先針對電致色變薄膜進行基本性質量測與分析，在瞭解了兩變色材料的電化學及光學性質之後，再針對PANI-PEDOT電致色變元件做一系列的探討，包括元件之著、去色電壓對穿透度調幅及長期操作穩定性的影響，以及推導出當兩極電量比不同時，元件所應具有的穿透度調幅之理論設計方程式，最後並使用離子液體做為電解質，以尋求元件之最佳效能。 針對PANI薄膜，其操作電位窗調控在-0.5 V至0 V，並且由光譜分析中可得知，若於電解質中加入少量的質子酸將有助於提升薄膜的穩定性。另外，由著色效率分析可得知，PANI薄膜具有三個階段的著色效率值，本研究所選定的操作電位範圍(-0.5 ~ 0 V)之著色效率值為25 cm2/C (at 570 nm)。從EQCM的分析中顯示：PANI薄膜於氧化還原時並非只以ClO4-的遷入與遷出維持薄膜的電中性，反而有部分為利用陽離子來平衡薄膜的電中性。對於PEDOT薄膜而言，其操作電位窗選定在0.3 V至-1.0 V間，並且由著色效率的量測計算得知其著色效率值約為206 cm2/C (at 570 nm)，且為此系統中主要貢獻顏色變化的材料。而從EQCM的分析中顯示其質量隨著操作圈數的增加而增加，其原因可能是由於PEDOT薄膜的表面結構較為多孔，溶劑分子(propylene carbonate)較有可能伴隨著陰離子進入薄膜使薄膜質量增加，或是溶液中移動速度較快的陽離子(H+ and Li+)進入薄膜以平衡電荷，而阻檔了陰離子的遷出。 PANI-PEDOT電致色變元件在以去色電壓為-0.6 V、著色操作電壓為1.0 V的操作電位連續操作之下，位於波長570 nm的去色態穿透度約為58~62%，而著色態穿透度約為15~20%，穿透度調幅約有40~45%。元件在操作11,400圈後之穿透度調幅為41.6%，為初始的96%，23,200圈時為33.8%，為初始的78%。元件之著色響應時間為1.1 s，而去色響應時間為0.4 s。而元件於波長570 nm時之著色效率為285 cm2/C (at 570 nm)，此數值與PANI與PEDOT著色效率的加成近似，顯示互補式電致色變元件之著色效率約為兩電致色變薄膜著色效率的和。另外在固定PANI薄膜之電量，而改變PEDOT薄膜之電量的情形下，元件之反應電量約相等於PEDOT薄膜所具有的電量，並發現理論穿透度調幅與實驗值相當的吻合好。 將電解質由PC換為離子液體溶液後，元件操作至2萬圈時所殘存的穿透度變化百分比由上述PC系統中之78% (1.0 V著色，-0.6 V去色)變為離子液體系統中的85% (1.0 V著色，-0.7 V去色)，顯示使用離子液體做為電致色變元件之導離電解質可些微提升元件之穩定性。

In this thesis, two conducting polymers, polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) (PEDOT) were used to construct a complementary electrochromic device (ECD), in which PANI served as the anodically coloring material and PEDOT as the cathodically coloring one. After knowing the electrochemical and optical properties of these two materials, the effect of the coloring and bleaching voltages on the optical attenuation performance and the cycling stability of the ECD were discussed. Moreover, the design equations for the ECD with different charge capacity ratios (CCRs), and the use of ionic liquid as an electrolyte were also discussed. For PANI thin film, the operating potential window was controlled between -0.5 and 0 V. From the spectral analysis, the adding of proton into electrolyte enhanced the cycling stability. By the analysis of the coloration efficiency, PANI thin film has three values of the coloration efficiency. In the chosen operating potential (-0.5~0 V), the coloration efficiency was calculated to be 25 cm2/C. From the EQCM analysis, not only ClO4- dominated the neutrality of PANI but anion also played an important role. For PEDOT thin film, the operating potential window was controlled between 0.3 and -1.0 V and the coloration efficiency was calculated to be 206 cm2/C, so that it dominated the color change of the ECD. From the EQCM analysis, the mass of PEDOT thin film increased with cycling numbers. This may due to the porous morphology that the solvent (propylene carbonate) would accompany with cations being inserted into the PEDOT film or anions (H+ and Li+) with larger mobility being incorporated into the film first and then blocked the expulsion of anions. The bleached and colored state transmittances at 570 nm of the PANI-PEDOT ECD were 58~62% at -0.6 V and 15~20% at 1.0 V, respectively, with delta T of about 40~45%. After 11,400 cycles, delta T of the ECD was 41.6%, which was 96% of its initial value; after 23,200 cycles, delta T of the ECD was 33.8%, and was 78% of the initial value. The response times for the coloring and bleaching processes were 1.1 s and 0.4 s, respectively. The coloration efficiency of the ECD was 285 cm2/C at 570 nm and this value was quite close to the sum of the coloration efficiency of each EC material. The optical attenuation performances of ECDs with different CCRs were also measured. The consumed charges of the ECDs were found to be equal to the charge capacity of PEDOT and the experimental data were fitted well by the design equations. By choosing ionic liquid as an electrolyte, ΔT remained 85% of the initial value after 2 x 104 cycles. This shows that electrolyte is an important issue for the cycling stability.