Research Of Bistable Three-state Electrochromic Devices

The electrochromic device?ECD?has a wide application prospect in the fields of building energy-saving materials,electronic displays,anti-counterfeiting equipment,and has become one of the research hotspots in the field of optoelectronic functional materials and devices.Among them,the reversible metal electrodeposition type ECD has the advantages of multi-color state and fast response speed,but the traditional electrodeposition ECD can only work in the power-on state,and it is difficult to maintain the long-term stability of the device coloring state in the power-off state,which greatly increases energy consumption and limits its application.Therefore,the development of ECD without voltage maintenance is of great significance for reducing device energy consumption and expanding application scenarios.This paper proposes and mainly studies a bistable-tri-state deposition type ECD based on the rough surface of WO₃ nano-island particles.The main content of the paper is as follows:Firstly,the preparation method of reversible metal electrodeposition ECD rough layer was studied.The rough layer structure is the key to the formation of the black state of the metal reversible electrodeposition type ECD.In this paper,a radio frequency magnetron sputtering technology is proposed to prepare WO₃ nano-island particles through Ag-induced growth on a transparent substrate of Indium Tin Oxide?ITO?.The size and morphology of WO₃ nanoparticles prepared by this method are stable,high repeatability and simple preparation.In the study,the surface of the sample was treated with HNO₃ solution for 45 s to improve the transmittance of the sample.Through the exploration and characterization,it was found that the sputtering power was 200 W,the oxygen flow rate was 40 sccm,the argon flow rate was 54 sccm,and the working pressure was 4.2×10^-1 Pa.With a sputtering time of 30 min,the highest transmittance of the sample after treatment with a 1.6 mol/L HNO₃ solution for 45 s is about 77.7%.The particle size and diameter are mainly around 300 nm,and the RMS roughness is 74.1 nm.The particle size is relatively uniform,suitable as rough layer for metal reversible electrodeposition type ECD.Secondly,on the basis of the above,a conventional reversible metal electrodeposition type three-state ECD based on the rough surface of WO₃ nano-island particles was prepared.The initial state transmittance of the device was tested through optical and electrochemical performance tests of the device to be approximately 67.9%and the black state transmittance was at least 2.5%,specular state reflectivity is as high as 95.4%,device black state coloring response time is about 11 s,black state fading response time is about 22 s,mirror state coloring response time is about 8 s,and mirror state fading response time is 16 s.After 500 CV cycle tests,the electrochemical performance remains stable.In addition,due to the traditional packaging method of punching and heat sealing film,the sealing of the device is poor.To solve this problem,the side opening method is adopted,and polydimethylsiloxane?PDMS?is used as the auxiliary packaging material.The device's hermeticity is improved,and the device remains effective after 7 days.Finally,a bistable-tri-state deposition ECD based on ionic liquid was prepared.Based on the traditional three-state device using the rough surface of WO₃ nano-island particles,the surface of ITO transparent electrode was bombarded with oxygen plasma and?3-mercaptopropyl?trimethoxysilane?MPTMS?solution pretreatment and electrolyte were used.An ionic liquid is introduced into the anion barrier layer to realize a bistable-tri-state reversible metal electrodeposition electrochromic device.Based on three different groups of ionic liquids 1-butyl-3-ethylimidazole bromide?[BEIM]Br?,1-hexyl-3-methylimidazole bromide?[HMIM]Br?,1-hexyl-3-butylimidazole Bromine salt?[HBIM]Br?prepared three groups of devices and tested the performance of the three groups of devices.It was found that the overall performance of the[BEIM]Br device based on ionic liquids was good,and its initial transmittance was about 66.5%.The black state transmittance is low as 2%,and the specular state reflectance is as high as 98.3%.After the device is removed from the voltage,the black state stabilization time reaches30.4 min and the mirror state stabilization time is about 16.7 min,which achieves the stability of the coloration after the device is powered off.In addition,the mechanism of the influence of the introduction of ionic liquid on the electrochromic performance of the device is analyzed in this paper,which provides a useful reference for further improving the light modulation amplitude and long-term stability of the device.