On the Optimization and Long-term Stability of the Electrochromic Devices Assembling with Conducting Polymers PEDOT or Its Derivative and Prussian Blue
|關鍵字:||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)||公開日期:||2004||摘要:||本論文探討電致色變技術(Electrochromic technologies)的基礎性質與其應用性。電致色變現象泛指當材料被施加不同直流電壓或電流時，該材料會可逆地改變對可見光的吸收度進而呈現不同的顏色變化。本研究首次提出以導電高分子ploy(3,4-ethylenedioxythiophene) (PEDOT)或其衍生物poly(3,3-dimethyl-3,4-dihydro-2H-thieno [3,4-b][1,4]dioxepine)(PProDOT-Me2)與無機材料普魯士藍(Prussian blue，PB)搭配，組成有機-無機互補式電致色變系統。
實驗中分別以定電位(1.2V vs. Ag/Ag+)電聚合導電高分子PEDOT (或PProDOT-Me2)與定電流(-20 μA/cm2)還原析鍍PB於導電玻璃ITO上，接著以循環伏安法、紫外光-可見光光譜儀與電化學微量石英震盪天秤對電致色變薄膜進行分析；在1.0 M LiClO4/PC 溶液中，PB在-0.9V(vs. Ag/Ag+)還原為無色，0.4V(vs. Ag/Ag+)氧化為藍色，能可逆地進行氧化還原反應；PEDOT則經由陰離子(ClO4-)的去參雜呈現深藍色(-1.2V vs. Ag/Ag+)，而隨施加電位往正方向增加，薄膜轉變為淡藍色(0.3V vs. Ag/Ag+)，在590 nm下的穿透度變化(ΔT)為56.4%；PProDOT-Me2則可以提供深藍紫色的還原態(-0.8V vs. Ag/Ag+)與透明無色的氧化態(0.4V vs. Ag/Ag+)，ΔT高達68.4%。
接著以PEDOT-PB元件分析元件性能最適化參數，元件在著、去色態分別呈現深藍色與淡藍色；實驗中獲得元件安全著、去色操作電壓分別為-1.5V(PEDOT vs. PB)與0.6V(PEDOT vs. PB)，在此電壓下，元件在連續152,140圈的階梯循環測試(Cycling stability test)後，ΔT仍維持在39%；在兩極電量密度搭配上，以元件安全著、去色電壓操作，元件ΔT在兩極電量密度比(R)接近1時具有最大值；此外，元件(0.50<R<1.52)在長期靜態操作穩定性測試上(Long-term at-rest stability test)，當R值範圍控制在0.79<R<1.15時，經過100天的測試後，元件ΔT仍維持在50%以上；電解質鹽類濃度則對元件性能影響不大，經過140天的靜態操作穩定性測試，元件ΔT衰退皆不到10%；以上顯示PEDOT-PB元件在參數最適化後，元件循環操作與靜態操作穩定性皆比文獻中以PEDOT為主的電致色變元件來得佳。
將上述最適化參數應用於PProDOT-Me2-PB元件，獲得更佳的元件性能表現:包括60.1% (11.0%~71.1% at 578 nm)的ΔT與450 cm2/C以上的著色效率值；PProDOT-Me2-PB元件以-1.2V(PProDOT-Me2 vs. PB)著色、0.6V(PProDOT-Me2 vs. PB)去色，在連續操作342,250圈後，元件ΔT維持在54.7% (ΔTmax = 57.6%)，而另一元件在靜態操作上，140天之後的元件ΔT也維持在57.2% (ΔTmax = 59.9%)，顯示PProDOT-Me2-PB元件能表現出更良好的穩定性。
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.
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