Research On Electro-modulated Spectral Responsive Materials And Devices

Electro-modulated spectral responsive devices based on reversible electrodeposition,also being called electrochromic devices based on reversible electrodeposition,are promising for application in light modulations and smart windows owing to their simple sandwich-type structure,facile and low-cost fabrication.Their optical properties can be manipulated via deposition of metal?copper,bismuth,plumbum,nickel,silver,etc.?onto transparent conducting electrode under an applied electrical voltage,and dissolution of metal back into electrolyte upon removal of the voltage.Usually,appropriate electrode surface modification may trigger reversible and multiple color states of the electrodeposition-based electrochromic device due to the absorption and/or multiple scattering of light of the modified electrode surface.The correlation between spin-coating and dip-coating process engineering,morphological features of titanium dioxide?TiO₂?thin films,i.e.thickness and roughness,as well as the performance of electrochromic devices,i.e.optical contrast,switching time,coloration efficiency,cycling stability,and memory effect,were researched in this dissertation.Moreover,the influnces of porous TiO₂ thin film on the performance of electro-modulated spectral responsive devices,i.e.optical contrast,switching time,coloration efficiency,memory effect,and cycling stability,were also investigated in this dissertation.The contents are divided into three parts shown as follows.1)TiO₂ nanoparticles were modified onto a fluorine-doped tin oxide?FTO?via spin-coating technique,followed by sandwiching a suitable amount of gel electrolyte between the modified FTO electrode and a flat FTO electrode to fabricate the electrodeposition-based electro-modulated spectral responsive device with reversible three-state optical transformation?transparent,mirror,and black?.A systematic study of correlation among electrode modification condition?the TiO₂ nanoparticle size,rotation speed,Ti02 precursor concentration,and repeating times?and morphological features of Ti02 thin films,as well as the performance of electro-modulated spectral responsive devices,i.e.optical contrast,switching speed,corolation efficiency,memory effect,and cycling stability,were investigated,which reveals that the performance of the three-state electro-modulated spectral responsive device can be adjusted by simply manipulating the electrode surface modification conditions.The optical contrast of the modified electro-modulated spectral responsive device was increased with the decreased thickness of Ti02 thin film,which were manipulated by using smaller nanoparticle size,higher rotation speed,lower precursor solution concentration,and less rotation number.The switching time and memory time of the modified device was strongly influenced by the surface roughness of the spin-coated TiO₂ thin film,with rougher surface providing large surface area to speed up the coloration time,slow down the bleaching time,and increase the memory time of the device.High coloration efficiency of 32.7cm/C and decrement rate of optical transmittance contrast of only 9.6%were exhibited for TiO₂ thin film prepared with nanoparticle size of 5?10 nm rotation speed of 2000 rpm,and repeating time of 1,with improved coloration efficiency and cycling stability obtained for device prepared with lower precursor concentration.Therefore,optimized performance of three-stated electro-modulated spectral responsive device could be obtained by properly manipulating the electrode modification conditions.The results in this study will provide valuable guidance for rational design of electro-modulated spectral responsive device with satisfactory performance and the TiO₂ nanoparticle-modified device with reversible three-state optical transformation may have various applications,such as information displays and light-modulation devices.2)Multi-state electrodeposition-based electro-modulated spectral responsive devices with reversible three-state optical transformation were successfully prepared via a facile and well-controlled dip-coating technique.The correlation among dip-coating process engineering and the morphological features of the TiO₂ nanoparticle-modified FTO electrodes,i.e.thickness and roughness,as well as the optical behavior of the fabricated devices,i.e.optical contrast,switching time,coloration efficiency,memory effect,and cycling stability were systematically studied.The optical properties of the assembled electrodeposition-based electro-modulated spectral responsive devices,i.e.optical contrast,switching time,coloration efficiency,cycling stability,and memory effect,were strong dependent on the thickness and roughness of the deposited Ti02 thin films,which were heavily influenced by the dip-coating process engineering.The thickeness of the deposited TiO₂ thin films were increased with the increase of nanoparticle size,lifting speed,precursor concentration,and dipping number.Rough surfaces with more nanoparticle agglomeration were obtained for TiO₂ thin film prepared with larger nanoparticle size,lower lifting speed,higher precursor concentration,and more dipping number.For the modified devices,higher optical contrast?48%?,faster switching speed?6.2 seconds for coloration and 19.6 seconds for bleaching?,higher coloration efficiency?27.0 cm2/C?,and improved cycling stability?the decrement rate of optical transmittance contrast of 27%?after 1500 cycles were obtained for device prepared with nanoparticle size of 5?10 nm,while longer memory time of 22.2 min was obtained for device prepared with nanoparticle size of 100 nm.Electrodeposition-based electro-modulated spectral responsive device prepared with lower lifting speed exhibited higher optical contrast,faster coloration speed,higher coloration efficiency,and longer memory time,while faster bleaching speed,and improved cycling stability were obtained for device prepared with higher lifting speed.Improved optical contrast,bleaching speed,and coloration efficiency were observed for device prepared with lower precursor concentration,while improved coloration speed and cycling stability were obtained for device prepared with higher precursor concentration.Moreover,optical contrast,switching speed,coloration efficiency,and cycling stability were all decreased for device prepared by repeating dipping.The high controllability of dip-coting technique and the obtained correlation among dip-coating process engineering and the morphological feature of the Ti02 nanoparticle-modified FTO electrodes,as well as the optical performance of the fabricated devices provide valuable guidance for rational design and performance optimization of the electrochromic device with required optical properties.The Ti02 nanoparticle-modified device with reversible three-state optical transformation may have various applications,such as information displays and light-modulating devices.3)Porous TiO₂ thin film was modified onto FTO electrode surface via template method by using polystyrene?PS?microspheres.Electrodeposition-based electro-modulated spectral responsive device with reversible three-state optical transformation?transparent,mirror and black?was fabricated subsequently by sandwiching a suitable amount of gel electrolyte between the modified FTO electrode and a flat FTO electrode.The correlation between the morphological feature of the TiO₂ nanoparticle-modified FTO electrode and the optical performance of the fabricated device was inversitgated.Compared with non-porous TiO₂ thin film,the porous one exhibited uniform and flat surface with less TiO₂ nanoparticles and uniform distribution of pores and grains.Higher optical contrast?69.6%?,faster switchting speed?4.4 seconds for coloration and 23.2 seconds for bleaching?,higher coloration efficiency?33.8 cm2/C?,improved memory effect?memory time of 28 min?and cycling stability?the decrement rate of optical transmittance contrast of only 9.6%?were obtained for electrodeposition-based electro-modulated spectral responsive device prepared with porous TiO₂ thin film.The porous Ti02 thin film modified device with reversible three-state optical transformation provides new ways for its optimization and application.