Research On Driving Vohage And Structure Optmization Of Flexibe Displays

Electrochromic(EC)materials and EC devices(ECDs)have attracted increased attention for their great applications in modern world.At present,some ECDs,such as smart window,anti-glare car rearview mirror,etc.,have even been commercialized.EC phenomenon was firstly observed in 1953,and from then,Tungsten trioxide(WO3),prussian blue(PB)and other inorganic electrochromic materials and organic small molecules and polymer electrochromic materials have always been a research hot topics.In terms of material properties,most of the inorganic electrochromic materials have good thermal stability and radiation resistance,while organic electrochromic materials are more likely to realize rich colors and rapid response.The conductive polymer represented by poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid(PEDOT:PSS)has high conductivity,good stability,high contrast,and is favored in the electrochromic fieldFor a long period up to present,EC related studies are mainly focused on the synthesis of new EC materials and modification of EC materials to improve the device performance."Smart window" and display devices are two key kinds of ECDs,and for both kinds of ECDs,the effective operation voltage regulation and high contrast are crucial,and thus should be of significant values for study.However,there is little research on the work voltage regulation of ECDs and how to improve the ECD performance via device design and optimization.In this thesis work,we have mainly studied these two aspects.The performance of electrochromic devices based PEDOT:PSS have been improved by the design and optimization of devices,such as operation voltage,threshold voltage and optical contrast.What's more,we have developed a new structure of electrochromic windows.The main work is as follows:(1)The performance comparison of ECDs with typical structure based on three commonly used EC materials,WO3,PB,and PEDOT:PSSThree ECDs with typical structure based on the three EC materials(WO3,PB,and PEDOT:PSS)were fabricated.These devices show high optical contrast of>60%,and the ECDs based on WO3 and PEDOT:PSS show relatively fast response with coloring/bleaching time of<10 s,while the ECDs based on PB show slow response with coloring/bleaching time of>40 s.In addition,ECDs based on WO3 are fabricated by vacuum magnetron sputtering with relatively high cost,and ECDs based on PB and PEDOT:PSS are fabricated by solution methods(wire bar coating,screen printing)with rather low cost.For quick response,simple process,and low cost,PEDOT:PSS has been chosen for the further studies in this thesis work.(2)Realization of controlling the performance,especially the driving voltage and response time,via device design and adjusting the electrode materialsWe have prepared ECDs based on PEDOT:PSS with two different vertical structures:the four-layer structure(a transparent conductive electrode,EC material,electrolyte,conductive bottom electrode)and the five-layer structure.In comparison with the four-layer structure,an ion storage layer has been added between the electrolyte and conductive bottom electrode in the five-layer structure.For these ECDs,different conductive bottom electrodes,including ITO,Ag,Ti,C,Ni and Au,have been applied to investment the influence of the electrode on the device performance,especially the operation voltage.The results show that,A,The five-layer devices with the introduction of ion storage layer can effectively reduce the operation voltage of the device;and B,The bottom electrode material can adjust the operation voltage in a large extent:from 0.74 to 1.35 V and from 0.31 to 0.69 V for the operation voltage in coloring and bleaching processes,respectively.In addition,the ECDs with Ti electrode show significantly reduced response time as low as 0.75 s.(3)Novel "three-electrode transmission ECD" with high contrastIn this thesis work,ECDs with a novel "three-electrode" structure(counter electrode,working electrode,and sacrifice electrode)using PEDOT:PSS as both electrochromic and ion storage layer have been developed.This new device structure has effectively solved the problem that the EC layer and ion storage layer cannot be the same(with same polarity)in one traditional transmission ECD,and thus open a new way to achieve high performance transmission ECDs without limitation of the matching of EC and ion storage materials.In our experiments,the "three-electrode"ECDs based on PEDOT:PSS show extremely low transmittance of 2.7%at colored state and high optical contrast of 58.2%.