Investigation On Structure And Performance Improvement Of Hybrid Electrochromic Devices

With the growing energy crisis,smart window technology,which has great potential for application in the field of energy efficiency in buildings,is gradually coming into the limelight.Electrochromism,as an alternative to smart windows,is receiving more and more attention due to its novelty and functionality.Electrochromism in a broad sense can be defined as the phenomenon of a stable and reversible change in the optical properties(transmittance,reflectance or absorbance)of a material(device)in the presence of an applied electric field,manifested externally as a change in color state.A variety of applications have been developed for the properties of electrochromic devices,such as anti-glare mirrors,aircraft portholes,electronic displays,mobile phone back covers,etc.The variety of applications also places high demands on the structure and performance of electrochromic devices.In general,electrochromic devices can be divided into solution,solid film and hybrid types according to the state of the electrochromic material and the charge storage substance.Solution type devices are suitable for scenarios where memory function and bleaching speed are not required as the materials are all completely dissolved in the electrolyte;solid film type devices require a good match between the working electrode and the counter electrode and require a high level of preparation and production processes;while hybrid type devices are combination of the previous two,fixing the electrochromic material in the form of thin film on the substrate and introducing redox couples in the electrolyte to balance charge,which has excellent optical modulation ability and good stability at the same time.The work in this dissertation is based on improving the performance of hybrid electrochromic devices in terms of response speed and transmittance modulation.In Chapter 3,we experimentally identified a contact potential difference between WO3 and the polymer poly(3,4-(2,2-dimethyl-propylenedioxy)thiophene)(PProDOTMe2)and that PProDOT-Me2 significantly enhances the electrochemical activity of the Br-/Br3-redox couple.PProDOT-Me2 was therefore used as the catalytic counter electrode for WO3 and the Br-/Br3-redox couple was introduced into the electrolyte to act as a charge balancing substance.The device in this system has a significantly lower driving voltage,a significantly faster response speed and can achieve rapid selfbleaching in short-circuit state.The device designed in this work therefore have broad,long-term potential for specific electrochromic applications where self-bleaching is required,such as in auto-dimming rear-view mirrors and anti-glare glass.In Chapter 4,on the basis of the above work,we have tried to place PProDOT-Me2 next to WO3 as a catalytic material in order to solve the problem of slow bleaching of WO3-based photovoltaic electrochromic devices.The experimental results show that PProDOT-Me2 exhibits better catalytic performance than Pt,resulting in an improved bleaching rate,enabling the replacement of the noble metal Pt in this structure of device,and its low price makes it possible to apply self-powered electrochromic windows over large area.In Chapter 5,we focused on improving the transmittance modulation capability of electrochromic devices.Currently,it is difficult to obtain devices with complete isolation of light(i.e.0%transmittance)in colored state due to the performance limitations of a single material.Since the polymeric material PProDOT-Me2 provides a rough surface along with excellent electrochromic properties,we have introduced a metal cation Ag+ that can be reversibly electrodeposited into the electrolyte of a hybrid type device based on PProDOT-Me2.Through the coloring of the electrochromic material and the absorption of light by the Ag particles,the device in the colored state can achieve a transmittance close to 0%in the 300-1500 nm waveband,allowing the device to switch between a transparent state and a all-black state.In this work,we have enhanced the response speed and transmittance modulation of hybrid electrochromic devices through structural and material optimisation.While providing new ideas for the design of electrochromic devices,we also expand the potential applications of electrochromic technology.