title: Achieving Low-Energy Driven Viologens-Based Electrochromic Devices Utilizing Polymeric Ionic Liquids.
abstract: Herein, three kinds of viologens-based electrochromic devices (ECDs) (heptyl viologen (HV(BF4)2), octyl viologen (OV(BF4)2), and nonyl viologen (NV(BF4)2)) were fabricated utilizing ferrocene (Fc) as a redox mediator. Among them, the NV(BF4)2-based ECD exhibits the highest coloration efficiency (36.2 cm2/C) owing to the lowest driving energy. Besides, switching between 0 and 1.2 V, the NV(BF4)2-based ECD shows a desirable initial transmittance change (ΔT = 56.7% at 605 nm), and long-term stability (ΔT = 45.4% after 4000 cycles). Furthermore, a UV-cured polymer electrolyte containing polymeric ionic liquid (PIL, 1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) and ethoxylated trimethylolpropane triacrylate (ETPTA) was introduced to the NV(BF4)2-based ECD. By controlling the weight percentage of the PIL, different curing degrees of the polymer electrolytes were obtained and led to an improved stability of the NV(BF4)2-based ECD because of the immobilization of NV(BF4)2. This observation was explained by calculating the apparent diffusivity (Dapp) of the redox species in the NV(BF4)2-based ECD under various curing degrees. In addition, increasing the amount of PIL leads to a lower driven energy needed for the NV(BF4)2-based ECD, following the same trend as the value of Dapp. Among all NV(BF4)2-based ECDs, 20 wt % of PIL addition (20-PIL ECD) exhibits large transmittance change (ΔT = 55.2% at 605 nm), short switching times (2.13 s in coloring and 2.10 s in bleaching), high coloration efficiency (60.4 and 273.5 cm2/C at 605 nm, after excluding the current density at the steady state), and exceptional cycling stability (ΔT = 53.8% after 10,000 cycles, or retained 97.5% of its initial ΔT).
authors.affiliation: Department of Chemical Engineering, National Taiwan University , No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan.
authors.forename: Hsin-Che
authors.initials: HC
authors.lastname: Lu
authors.affiliation: Department of Chemical Engineering, National Taiwan University , No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan.
authors.forename: Sheng-Yuan
authors.initials: SY
authors.lastname: Kao
authors.affiliation: Department of Chemical Engineering, National Taiwan University , No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan.
authors.forename: Hsin-Fu
authors.initials: HF
authors.lastname: Yu
authors.affiliation: Department of Chemical Engineering, National Taiwan University , No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan.
authors.forename: Ting-Hsiang
authors.initials: TH
authors.lastname: Chang
authors.affiliation: Department of Chemical Engineering, National Taiwan University , No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan.
authors.forename: Chung-Wei
authors.initials: CW
authors.lastname: Kung
authors.affiliation: Department of Chemical Engineering, National Taiwan University , No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan.|Institute of Polymer Science and Engineering, National Taiwan University , No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan.
authors.forename: Kuo-Chuan
authors.initials: KC
authors.lastname: Ho
keywords: UV-curing; diffusion coefficient; electrochemistry; electrochromic devices (ECDs); gel electrolytes; ionic liquids; polymer electrolytes; viologens