Investigations On New Self-Erasing Multicolor Electrochromic Device And Fast-switching Photovoltachromic Device

Electrochromic materials are those which can display optical properties’ change under applied potentials,the appearance’s changes often involved with color and transmittance change.The phenomenon of colorful variations originates from ions’extraction and insertion processes under exterior electrical fields.Electrochromic materials’ reduced and oxidized states show different optical characteristics.The electrochromic materials with great ability to switch optical contrast have been utilized in many areas,including smart window,colorful goggles,and display.With the development of the society,researchers from different fields tried to incorporate electrochromic technique with dye sensitive solar cell(DSSC),the obtained photoelectrochromic devices(PECD)can change optical contrast spontaneously under sunlight without exterior applied voltages.PECD has a great potential in the construction of energy efficiency buildings.Most of the electrochromic devices are assembled with solid electrochromic films,in order to keep the charge balance of the device,a charge-storage layer on the counter electrode is needed.The charge-storage layer must have similar charge capacity with the electrochromic film.In the middle of the two electrodes is the electrolyte which can transport the ions.This classical device structure is called as sandwich Type structure.Due to the sandwich structure,there are strict restrictions on the charge capacity’s matching property of the two electrodes.And the counter electrode required to be transparent during the device’s coloring process,especially when the device is kept in bleached state.The searching and preparing process of a qualified counter electrode film often involves with a series of complicated operations,and thus limits the development of the solid film electrochromic device.Firstly,we incorporated a redox couple of Br-/Br3-into the electrolyte which can only be used to carry the ions.By the redox reactions of Br-/Br3-,the charge variation could be balanced without a conventional charge storage layer on the counter electrode.By adopting this strategy,the complicated preparation process of the counter electrode could be avoided.Therefore,this strategy simplified the fabricating procedure of the solid film Type device.Since the counter electrode film would not need to keep the charge balance for the whole circuit of the device,the counter electrode could be replaced by an ordinary electrochromic film so that each electrochromic film could display an independent performance,the optical performances-could be increased in this way.In this work,two classical cathode electrochromic materials,TiO2 and poly(3,4-(2,2-dimethyl-propylenedioxy)thiophene)(PProDOT-Met)were incorporated in a single device.Each material successfully exhibited an independent electrochromic change under exterior voltages.A multicolor electrochromic device could be obtained without a complicated synthesizing procedure for a new material.Secondly,the electrochromic technique was combined with DSSC technique to make an self-powered device called as PECD.The light-induced current of the DSSC part under sunlight could drive the electrochromic film to change color.Due to WO3’s brilliant cyclic stability and optical modulation capability,the researchers always devoted their efforts into using WO3 as the electrochromic material in the self-powered device.In order to make sure WO3 had a short response time of switching its color under sunlight,the scarce and expensive metal platinum(Pt)must be needed.Due to the high price of Pt,the development of WO3-based PECD has been severely restricted.While in this research,we found that the material which was used to accelerate the switching speed didn’t have to stick with Pt,the low-cost organic material PProDOT-Me2 could replace Pt to have a better performance under same test parameters.We believe this finding would benefit the whole PECD industry based on WO3.