All-solid-state electrochromic device (ECD) has received considerable attention with the development of energy-efficient and high stable smart windows. Polymer electrolyte is necessary for ECD instead of liquid electrolyte to prevent leakage because of its safety and durability in real outdoor condition. Therefore, research has been focused on polymer systems containing PMMA [1], PEO [2], UV-crosslink network [3] and etc. However, several drawbacks i.e. yellowish color, haze, and complex multi-step process still remain. To overcome these problems, we tried to improve optical transparency of polymer electrolyte with a simple and easy fabrication method.

In this research, we prepared a transparent and free-standing gel polymer electrolyte with excellent mechanical flexibility and elongation in one-step process. Three-dimensional acrylate crosslinking network has formed directly through UV irradiation under co-presence of the PVdF-HFP and LiClO₄ salt. To obtain optimum composition, variables including mono-, di-acrylate oligomers, PVdF-HFP, and plasticizers were controlled. Electrolyte was analyzed with regard to physical and chemical characterization using SEM, FT-IR, DSC, Tensile test, and ion conductivity measurement, etc. In order to fabricate electrochromic device, electrochromic film was deposited by Nano Particle Deposition System (NPDS), which is a facile dry-deposition method to coat ceramic powders using high impact energy when the collisions between particles and substrate occur [4]. Electrochromic performance of the fabricated cell was evaluated by in situ UV-Vis spectroscopy and electrochemical analysis techniques, such as Electrochemical Impedance Spectroscopy(EIS), and Cyclic Voltammetry(CV), etc.

Finally, it was confirmed that extremely clear ion conducting membrane was easily fabricated in one-step and successfully applied to ECD at ambient temperature. The transmittance of the polymer electrolyte showed over 80 % and the fabricated ECD cell with polymer electrolyte exhibited its transmittance change greater than 50 % at its wavelength of 800 nm under 3 V which shows almost similar performance of the cell using liquid electrolyte. Therefore, we have developed one-step process to fabricate highly transparent and free-standing polymer electrolyte, to obtain high performance electrochromic device.

[1] J. Phys. Chem. B, 2009, 113, 8006–8010

[2] Scientific Reports 2016, 6, 19892

[3] Membranes, 2012, 2, 687-704

[4] Applied Surface Science, 2016, 377, 370–375