Organic Electrochromic Devices Based on Stable Free Radical (TEMPO) and Conducting Polymers

• Main Authors: Chih-Wei Hu, 胡致維
• Other Authors: Kuo-Chuan Ho
• Format: Others
• Language: en_US
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/99934364949853465096

博士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 99 === In this dissertation, the main propose is to investigate the electrochemical properties of the organic molecule 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and its applications for electrochromic devices. Firstly, we make a short introduce of electrochromic (EC) materials and devices and also a completed introduction of conducting polymers and its’ synthesis methods. The history and applications are discussed here. A stable organic radical, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), was studied. We employed TEMPO as a cathodic radical provider in propylene carbonate (PC) and poly(3,4-propylenedioxythiophene) derivatives (PProDOT-Et2) as an anodic electrochromic (EC) thin film, which was obtained through electropolymerization. By assembling them together in a device, the electrochemical and optical performances of this hybrid electrochromic device (ECD) showed reversible cycling stability and high absorbance attenuation in the visible range. By selecting proper electrolytes (LiClO4/PC) and controlling the deposited charge of the PProDOT-Et2 thin film, it was possible to obtain a transmittance change (ΔT) of up to 69% at 590 nm with no degradation after operating between -0.5 and 0.9 V for 10,000 cycles. We talk about TEMPO and two electrochromic (EC) materials, poly(3,4-ethylenedioxythiophene) (PEDOT) and heptyl viologen (HV(BF4)2) were utilized to fabricate a hybrid electrochromic device (ECD). PEDOT and HV(BF4)2 were respectively used as film and solution type cathodic EC materials. The novel ECD exhibited two-stage redox reactions with high absorbance attenuation in the visible region. With the variation of the operating voltage, a transmittance change (ΔT) of 20% at 610 nm was observed in the first stage (-0.5 ~ 0.8 V), and that of 68% was observed in the second stage (0.9 ~ 1.5 V). Furthermore, fast switching times of 6.9 and 2.1s were estimated for bleaching and darkening, respectively. The coloration efficiencies at 610 nm were found to be 171.9 cm2C-1 and 91.0 cm2C-1 for the first and second stages, respectively. Continuously, heptyl viologen (HV(BF4)2) works as the cathodic coloring solution (electrochromic), TEMPO as the anodic radical provider (ion-storage layer), and crystals of succinonitrile (SN)-plastic as the solid matrix. The electrochemical and electrochromic properties of HV(BF4)2 and TEMPO molecules are analyzed from their in a 0.1 M electrolyte of tetrabutylammonium tetrafluoroborate (TBABF4) in PC. 6 wt% silicon dioxide (SiO2) nanoparticles is added to the matrix to eliminate its crystalline nature. This all-solid-state ECD made with this non-crystalline solid matrix shows a high optical contrast with coloration efficiencies of ca. 65.5 and 342.2 cm2/C at 610 nm at two stages. The transmittance of the ECD at 610 nm has changed from 81% (bleached) to 6% (darkened), with an applied potential of 1.5 V. A novel hybrid type electrochromic device (ECD) was fabricated, using a stable TEMPO, polyaniline (PANI) and heptyl viologen (HV(BF4)2). PANI and HV(BF4)2 were used as film and solution type anodic and cathodic EC materials, respectively in chapter 6. TEMPO acts only as an ionic storage layer and works in pair with either of the electrochromic materials. With the variation of the operating voltage between 0 ~ 1.5 V the TEMPO-HV system showed electrochromism and a transmittance change (ΔT) of 46% at 550 nm. With the variation of the voltage between 0 ~ -1.0 V the TEMPO-PANI system showed electrochromism and a ΔT of 45% at 700 nm.