Abstract
Thermally stable TPA-OMe polyamide films with high transmittance modulation in response to applied potential are formed by facile ultrasonic spray-coating. Four processing conditions (Film A, Film B, Film C and Film D) through tuning both solution concentrations and deposition temperatures can be utilized for the formation of wet and dry deposited films with two film thickness intervals. The electrochromic results show that the dry deposited rough films at higher deposition temperature generally reveal a faster electrochromic response, lower charge requirements (Q) and less conspicuous color changes (smaller optical density change (ΔOD) and lightness change (ΔL*)) during the oxidation process as compared to the wet deposited smooth films at lower deposition temperature. Moreover, thicker electrochromic films from increased solution concentration exhibit more obvious changes between coloration and bleaching transition. All these four polyamide films display colorless-to-turquoise electrochromic switching with good redox stability. The large scale patterned electrochromic film and its application for assembled device (10 × 10 cm2 in size) are also produced and reversibly operated for color changes. These represent a major solution-processing technique produced by ultrasonic spray-coating method towards scalable and cost-effective production, allowing more freedoms to facilitate the designed electrochromic devices as required.
Highlights
Good reproducibility and precise coating if spraying ink solution consisting of good material solubility, volatile solvent used and suitable viscosity is readily prepared
Film A is obtained from triphenylamine-containing polyamides (TPA-OMe) polyamide solution of 8 mg ml−1 and heated at 40 °C; Film B: 8 mg ml−1 and 80 °C; Film C: 16 mg ml−1 and 40 °C; Film D: 16 mg ml−1 and 80 °C
It should be noted that four processing conditions for ultrasonic spray-coated electrochromic films were used here since the significant changes in electrochromic properties between all these films can be systematically observed and compared
Summary
Good reproducibility and precise coating if spraying ink solution consisting of good material solubility, volatile solvent used and suitable viscosity is readily prepared. Solution-processable electrochromic polymers which can be dissolved in common organic solvents and spray-coated onto substrate need to be further exploited in order to possess long cyclic life, bleaching/coloring efficiency and apply for large area and patterned solid state devices. How to control the processing parameters during the ultrasonic spray-coating process plays an important role for deposition of polyamides films with good electrochromic behavior. Wet/dry deposited electrochromic polyamides film (controlled by heating temperature) as well as film thickness (controlled by ink formulation) command the eventual performance metrics such as response time, optical density change (ΔOD), color efficiency (η), cycling stability capable of switching between the bleaching (neutral) and coloring (oxidized) state. A reliable and reproducible large scale spray deposition process demonstrated here are suitable for utilizing as integration into solid-state patterned ECD with the application of appropriate electrical potentials
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