Evaluation of Low Voltage operating multi-colored electrochromic device (ECD) based on dry-deposited V2O5

Abstract

Electrochromic device (ECD) reversibly changes color or transmittance by a redox reaction caused by the application of an external voltage and is drawing attention as a next-generation display device. V2O5 has multivalent states, and through this, various colors ranging from yellow to blue can be. So, it is attracting great attention as an electrochromic material. However, V2O5 has low charge storage properties, electrical conductivity, and ion diffusion coefficient, and has limitations in poor cyclic stability, so it is essential to overcome these limitations when manufacturing a V2O5- based electrochromic device. This study manufactures an ECD with improved durability using a V2O5 film fabricated using a Nano-Particle Dry deposition System (NPDS) as both electrodes, focusing on the idea that V2O5 can also be used as an anodic and cathodic electrochromic (EC) material. The V2O5 film deposited on both electrodes serves as a complementary layer during the redox reaction to balance the charge inside the device, thereby relieving the load applied to the ECD by enabling operation in the ±1V range. The fabricated ECD implemented different colors as opposite voltages were applied to both electrodes, while the electrolyte was made opaque so that the colors of the two thin films could be implemented independently without affecting each other. The fabricated ECD can implement three types of colors: yellow, green, and blue, and it takes 8 seconds to change color from blue to yellow, 8 seconds to change color from yellow to green, and 2 seconds to change color from green to blue. According to the CIE (International Commission on Illumination) analysis, the color difference (ΔE) between yellow and green was 36.30, the color difference between green and blue was 21.36, and the color difference between yellow and blue was 55.21, confirming the definite color change. Moreover, the fabricated ECD showed almost the same level of electrochromic performance even after 500 repeated runs. Furthermore, even in the 10,000 cycles Cyclic Voltammetry (CV) analysis, the charge capacity of the ECD was 47.31 mC/cm2, almost the same performance as the initial charge capacity value of 49.01 mC/cm2, proving the high durability of the device. In addition, we have developed a gel electrolyte based on LiTFSI-EMIMTFSI (1:9 mol%) that prevented deterioration in durability due to electrolyte leakage and bubbles in the device, which was problems with liquid electrolytes. Furthermore, the ionic conductivity of the electrolyte did not differ from that of the liquid electrolyte (σliq: 11.43 x 10-4 S/cm, σgel: 9.97 x 10-4 S/cm). Therefore, in this study, an ECD capable of coloration in a low voltage range of ± 1V was fabricated using a dry deposition method and an opaque electrolyte, and three types of colors were independently and vividly realized at both sides of the device. This unique type of device is expected to be useful in the functional electrochemical display field.