In-situ characterization of electrochromism based on ITO/PEDOT:PSS towards preparation of high performance device

Poly（3,4-ethylenedioxythiophene）：poly（styrenesulfonate）（PEDOT：PSS） is usually sandwiched between indium tin oxide（ITO） and a functional polymer in order to improve the performance of the device. However, because of the strong acidic nature of PEDOT：PSS, the instability of the ITO/PEDOT：PSS interface is also observed. The mechanism of degradation of the device remains is unclear and needs to be further studied. In this article, we investigate the in-situ electrochromism of PEDOT：PSS to disclose the cause of the degradation. X-ray photoelectron spectroscopy（XPS） was used to characterize the PEDOT：PSS films, as well as the PEDOT：PSS plus polyethylene glycol（PEG） films with and without indium ions. The electrochromic devices（ECD） based on PEDOT：PSS and PEG with and without indium ions are carried out by in-situ micro-Raman and laser reflective measurement（LRM）. For comparison, ECD based on PEDOT：PSS and PEG films with LiCl, KCl, NaCl or InCl_3 are also investigated by LRM. The results show that PEDOT：PSS is further reduced when negatively biased, and oxidized when positively biased. This could identify that PEDOT：PSS with indium ions from PEDOT：PSS etching ITO will lose dopants when negatively biased. The LRM shows that the device with indium ions has a stronger effect on the reduction property of PEDOT：PSS-PEG film than the device without indium ions. The contrast of the former device is 44%, that of the latter device is about 3%. The LRM also shows that the contrasts of the device based on PEDOT：PSS＋PEG with LiCl, KCl, NaCl, InCl_3 are 30%, 27%, 15%, and 18%, respectively.

WO_3 Anodic Oxide Film——I.Electrochromism and Auto-bleaching mechanism

Electrochromic and auto-bleaching processes at the WO2 anodic film in 0. 5 mol/L H2SO4 solution were investigated by cyclic voltammetry, a. c. impedance technique and photocurrent spectrometry. The colouration mechanism consists of hydrogen adsorption on the WO2 surface and the transport of H atoms in the WO, lattice. The bleaching process involves at least two steps: transport of interstitial H atoms and hydrogen desorption on the W surface, resulting in interstitial H+ ions; then extration of the H+ ions driven by the external electric field. The auto-bleaching arises from the hydroxylation due to both partial interstitial H atoms and a little of water contained in the film.

Fine-tuning redox ability of arylene-bridged bis(benzimidazolium)for electrochromism and visible-light photocatalysis

In this study,a series of arylene-bridged bis(benzimidazolium)triflates 1^(–)6^(^(2+))·2[OTf^(–)]were synthesized by grafting differentπ-linkers with benzimidazolium scaffolds.Among them,compound 1^(2+)·2[OTf^(–)]with anthracene as the linker exhibited remarkable electron transfer capabilities across four distinct redox states.The inclusion of an anthracene unit as theπ-linker contributes to its exceptional redox and optoelectronic characteristics.Consequently,1^(2+)·2[OTf^(–)]was successfully utilized as both an electrochromic molecule in an ECD under applied voltage for the first time,and a highly efficient photocatalyst for the formation of carbon–phosphorus bonds via visible-light-induced cross-dehydrogenative coupling reactions.

Electrochromism-induced adaptive fresh air pre-handling system for building energy saving

Building fresh air supply needs to meet certain regulations and fit people’s ever-growing indoor air quality de-mand.However,fresh air handling requires huge energy consumption that goes against the goal of net-zero energy buildings.Thus,in this work,an adaptive fresh air pre-handling system is designed to reduce the cool-ing and heating loads of HVAC system.The sky-facing surface of the system uses electrochromic mechanism to manipulate the optical properties and thus make full use of solar energy(solar heating)and deep space cold source(radiative cooling)by switching between heating and cooling modes.In the cooling mode,the sky-facing surface shows a transmittance of down to zero,while the reflectance is high at 0.89 on average.In the heating mode,the electrochromic glass is highly transparent,allowing the sunlight to reach the solar heat absorber.To obtain the energy-saving potential under different climates,six cities were selected from various climate regions in China.Results show that the adaptive fresh air pre-handling system can be effective in up to 55.4%time of a year.The maximum energy-saving ratios for medium office,warehouse,and single-family house can reach up to 11.52%,26.62%,and 18.29%,respectively.In addition,the system shows multi-climate adaptability and broad application scenarios,making it a potential solution to building energy saving.

Ultrastable Viologen Ionic Liquids-Based Ionogels for Visible Strain Sensor Integrated with Electrochromism,Electrofluorochromism,and Strain Sensing

Flexible electronics play a key role in the development of human society and our daily activities.Currently they are expected to revolutionize personal health management.However,it remains challenging to fabricate smart sensors with high robustness,reliability,and visible readout.Herein,high-performance electrochromic(EC),electro-fluorochromic(EFC),and double-network ionogels with excellent transmissivity,high mechanical robustness,and ultrastable reversibility are prepared by combination of thienoviologen-containing ionic liquids with poly(ethyl acrylate)elastomer.The ionogels exhibit good mechanical properties(1000%stretchability and 3.2 kJ m^(−2) fracture energy).The ionogel-based EC devices have a significantly simplified device fabrication process as well as superior cycling stability in which 88%of the contract ratio is maintained at 88%at 500 cycles,even after being stored for 2 years under ambient atmosphere(relative humidity:30%∼40%,25°C).The conductivity of ionogels showed a fast and reproducible response to strain,and the conductivity decreased with increased strain.By virtue of the EC and EFC properties of the thienoviologen component,the EC and EFC efficiency decreased with the increased strain loaded on the ionogels,and almost no EC or EFC phenomena were observed when the strain was above 300%.This feasible strategy provides an opportunity for the development of visible strain sensors to monitor the body’s movements through color and fluorescence emission.

Designing TiO_(2)/Au/Prussian blue heterostructures nanorod arrays for ultra-stable cycle and ultra-fast response electrochromism

Prussian blue(PB)is an anodic coloring candidate in the wide area of electrochromic(EC)applications.However,the co-influence of weak adhesion and low electrical conductivity leads to the poor stability and slow switching speed.To tackle this bottleneck,a novel TiO_(2)/Au/PB nanorod array is designed through hydrothermal and electrodeposition approaches on fluorine-doped tin oxide(FTO)glass.Such a designed ternary array structure could not only increase reactive site and conductivity,but also improve ion storage capacity and promote charge transfer,attributed to the synergistic effect of TiO_(2)/Au/PB core–shell heterostructure and the localized surface plasmon resonance(LSPR)effect of Au nanoparticles.Besides,density functional theory(DFT)calculation confirms the strong interaction between rutile TiO_(2)and FTO substrate,which contributes to the improvement of EC cycle stability.Benefiting from these effects,the TiO_(2)/Au/PB film shows a fast coloration/bleaching response of 1.08/2.01 s(2.17/4.48 s,PB film)and ultra-stable EC performance of 86.8%after 20,000 cycles(50%after 600 cycles,PB film).Furthermore,the high-intensity light source can be shot clearly by the designed and assembled EC iris device(ECID)with TiO_(2)/Au/PB film as an EC layer,while the photograph without an ECID is blurry,confirming the feasibility of the material in portable digital products.

Viologen-based flexible electrochromic devices

Electrochromic technology has gained significant attention in various fields such as displays,smart windows,biomedical monitoring,military camouflage,human-machine interaction,and electronic skin due to its ability to provide reversible and fast color changes under applied voltage.With the rapid development and increasing demand for flexible electronics,flexible electrochromic devices(FECDs)that offer smarter and more controllable light modulation hold great promise for practical applications.The electrochromic material(ECM)undergoing color changes during the electrochemical reactions is one of the key components in electrochromic devices.Among the ECMs,viologens,a family of organic small molecules with 1,1'-disubstituted-4,4'-dipyridinium salts,have garnered extensive research interest,due to their well-reversible redox reactions,excellent electron acceptance ability,and the ability to produce multiple colors.Notably,viologen-based FECDs demonstrate color changes in the liquid or semisolid electrolyte layer,eliminating the need for two solid electrodes and thus simplifying the device structure.Consequently,viologens offer significant potential for the development of FECDs with high optical contrast,fast response speed,and excellent stability.This review aims to provide a comprehensive overview of the progress and perspectives of viologen-based FECDs.It begins by summarizing the typical structure and recent exciting developments in viologen-based FECDs,along with their advantages and disadvantages.Furthermore,the review discusses recent advancements in FECDs with additional functionalities such as sensing,photochromism,and energy storage.Finally,the remaining challenges and potential research directions for the future of viologen-based FECDs are addressed.

Active and passive modulation of solar light transmittance in a uniquely multifunctional dual-band single molecule for smart window applications

Functional materials may change color by heat and electricity separately or simultaneously in smart windows.These materials have not only demonstrated remarkable potential in the modulation of solar radiation but are also leading to the development of indoor environments that are more comfortable and conducive to improving individuals'quality of life.Unfortunately,dual-responsive materials have not received ample research attention due to economic and technological challenges.As a consequence,the broader utilization of smart windows faces hindrances.To address this new generational multistimulus responsive chromic materials,our group has adopted a developmental strategy to create a poly(NIPAM)n-HV as a switchable material by anchoring active viologen(HV)onto a phase-changing poly(NIPAM)n-based smart material for better utility and activity.These constructed smart windows facilitate individualistic reversible switching,from a highly transparent state to an opaque state(thermochromic)and a red state(electrochromic),as well as facilitate a simultaneous dual-stimuli response reversible switching from a clear transparent state to a fully opaque(thermochromic)and orange(electrochromic)states.Absolute privacy can be attained in smart windows designed for exclusive settings by achieving zero transmittance.Each unique chromic mode operates independently and modulates visible and near-infrared(NIR)light in a distinct manner.Hence,these smart windows with thermal and electric dual-stimuli responsiveness demonstrate remarkable heat regulation capabilities,rendering them highly attractive for applications in building facades,energy harvesting,privacy protection,and color display.

Surface Deposition of Ni(OH)_(2) and Lattice Distortion Induce the Electrochromic Performance Decay of NiO Films in Alkaline Electrolyte

NiO,an anodic electrochromic material,has applications in energy-saving windows,intelligent displays,and military camouflage.However,its electrochromic mechanism and reasons for its performance degradation in alkaline aqueous electrolytes are complex and poorly understood,making it challenging to improve NiO thin films.We studied the phases and electrochemical characteristics of NiO films in different states(initial,colored,bleached and after 8000 cycles)and identified three main reasons for performance degradation.First,Ni(OH)_(2)is generated during electrochromic cycling and deposited on the NiO film surface,gradually yielding a NiO@Ni(OH)_(2)core-shell structure,isolating the internal NiO film from the electrolyte,and preventing ion transfer.Second,the core-shell structure causes the mode of electrical conduction to change from first-to second-order conduction,reducing the efficiency of ion transfer to the surface Ni(OH)_(2)layer.Third,Ni(OH)_(2)and NiOOH,which have similar crystal structures but different b-axis lattice parameters,are formed during electrochromic cycling,and large volume changes in the unit cell reduce the structural stability of the thin film.Finally,we clarified the mechanism of electrochromic performance degradation of NiO films in alkaline aqueous electrolytes and provide a route to activation of NiO films,which will promote the development of electrochromic technology.

Electropolymerized films of redox-active ruthenium complexes for multistate near-infrared electrochromism,ion sensing,and information storage

This paper summarizes our recent progress on the preparations and applications of electropolymerized thin films of redox-active ruthenium complexes.Thin films of vinyl-functionalized diruthenium or ruthenium-amine conjugated complexes are prepared by reductive electropolymerization.The resulting films are useful for multistate near-infrared electrochromism,ion sensing,and mimicking flip-flop and flip-flap-flop logic gates.The oxidative electropolymerization of diruthenium complexes with two distal triarylamine units affords electropolymers with an alternating diruthenium and tetraphenylbenzidine structural unit.The applications of the resulting films in multistate near-infrared electrochromism and resistive memory are discussed.

Near-infrared electrochromism of multilayer films of a cyclometalated diruthenium complex prepared by layer-by-layer deposition on metal oxide substrates

A cyclometalated diruthenium complex 2 bridged by 1,2,4,5-tetra(pyrid-2-yl)benzene with six carboxylic acid groups at two ends was synthesized.Monolayer and multilayer films FTO/TiO2/(2)n(Zr)(n=1,2)and FTO/SnO2:Sb/(2)n(Zr)(n=1-4)have been prepared via interfacial layer-by-layer coordination assembly of 2 with zirconium(IV)ions.All films show two consecutive redox couples in the potential range between 0 and+1.0 V vs.Ag/AgCl.These films exhibit reversible near-infrared electrochromism upon switching of redox potential.The response time of the films on SnO2:Sb is around a few seconds,while that on TiO2 is around a few tens of seconds.The film deposition cycles were found to have a great impact on the electrochromic performance.Among six films examined,the two-layered film on SnO2:Sb displays the best balanced performance with a contrast ratio of 56%at 1,150 nm and good cyclic stability(9%loss of contrast ratio after 1,000 continuous double-potential-switching cycles),which is superior to that of the previously reported electropolymerized films of a related diruthenium complex with the same bridging ligand.In addition,the X-ray photoelectron spectroscopy,scanning electron microscopy,and electron transfer mechanism of these films have been investigated.

Thickness Dependence of Doping Level in Conducting Polymer Films:the Optical Contrast Optimization in Electrochromism as a Case Study

Doping plays an essential role in the properties of conducting polymers.Film thickness not only has a direct influence on their photoelectric properties,but also affects the doping ability,which may lead to the decline of capacitance and electrochromic properties caused by incomplete doping.Therefore,it is essential to study the quantitative relationship between doping level and film thickness in application.Herein,empirical formula between doping level and thickness was obtained by studying the spectroelectrochemistry behaviors of two different electrochromic materials,poly(N,N'-bis(3,5-(2-thienyl)-phenyl)-1,6,7,12-tetrachloroperylene-3,4,9,10-perylenetetracarboxylic diimide)(poly(Th-Cl-PBI))and poly(3,4-ethylenedioxythiophene)(PEDOT).The doping level is verified to be correlated to the reciprocal of the 3^(rd)power of film thickness.Experimental results fit these formulas very well,giving correlation coefficient R^(2)higher than 0.99.The optical contrast prediction of these two electrochromic materials is also used to verify this relationship formula.For the first time,we quantitatively connect these two important parameters of conducting polymers,doping level and thickness.

Exploring innovative synthetic solutions for advanced polymer-based electrochromic energy storage devices:Phenoxazine as a promising chromophore

The current investigation offers an innovative synthetic solution regarding electrochromic(EC)and energy storage applications by exploring phenoxazine(POZ)moiety.Subsequently,three POZ-based polymers(polyimide,polyazomethine,and polyamide)were synthesized to ascertain the superior performer.The polyamide exhibited remarkable attributes,including high redox stability during 500 repetitive CVs,optical contrast of 61.98%,rapid response times of 1.02 and 1.38 s for coloring and bleaching,EC efficiency of 280 cm^(2)C^(-1).and decays of the optical density and EC efficiency of only 12.18%and 6.23%after 1000 cycles.Then,the energy storage performance of polyamide PA was tested,for which the following parameters were obtained:74.7 F g^(-1)(CV,scan rate of 10 mV s^(-1))and 118 F g^(-1)(GCD,charging current of 0.1 A g^(-1)).Then,the polyamide was tested in EES devices,which yielded the following EC parameters:an optical contrast of 62.15%,response times of 9.24 and 5.01 s for coloring and bleaching,EC efficiency of 178 cm^(2)C^(-1),and moderate decays of 20.25%and 23.24%for the optical density and EC efficiency after 500 cycles.The energy storage performance included a capacitance of 106 F g^(-1)(CV,scan rate of 0.1 mV s^(-1))and 9.23 F g^(-1)(GCD,charging current of 0.1 A g^(-1)),capacitance decay of 11.9%after500 cycles,and 1.7 V retention after 2 h.Also,two EES devices connected in series powered a 3 V LED for almost 30 s.

Recent progress and future research directions for electrochromic zinc-ion batteries

In recent times,future energy storage systems demand a multitude of functionalities beyond their traditional energy storage capabilities.In line with this technological shift,there is active research and development of electrochromic-energy storage systems designed to visualize electrochemical charging and discharging processes.The conventional electrochromic-energy storage devices primarily integrated supercapacitors,known for their high power density,to enable rapid color contrast.However,the low energy density of supercapacitors restricts overall energy storage capacity,acting as a significant barrier to expanding the application range of such systems.In this review,we introduce electrochromic zinc(Zn)-ion battery systems,which effectively overcome the limitation of low energy density,and provide illustrative examples of their applicability across diverse fields.Although many recent research works are present for electrochromic Zn-ion batteries,little review has so far taken place.Our objective is to discuss on the current progress and future directions for electrochromic Zn-ion batteries,which are applicable for wearable electronics applications and energy storage systems.This review provides an initial milestone for future researchers in electrochromic energy storage and zinc-ion batteries,which will lead to a stream of future works related to them.

Inhibiting the phase transition of WO_(3)for highly stable aqueous electrochromic battery

Aqueous electrochromic battery(ECB)has shown intense potential for achieving energy storage and saving simultaneously.While tungsten oxide(WO_(3))is the most promising EC material for commercialization,the cycling stability of WO_(3)-based aqueous ECBs is currently unsatisfactory due to the repeated phase transition during the redox process and the corrosion by acidic electrolytes.Herein,we present a titanium-tungsten oxide alloy(Ti-WO_(3))with controllable morphology and crystal phase synthesized by a facile hot injection method to overcome the challenges.In contrast to conventional monoclinic WO_(3),the Ti-WO_(3)nanorods can stably maintain their cubic crystal phase during the redox reaction in an acidic electrolyte,thus leading to dramatically enhanced response speed and cycling stability,Specifically,when working in a well-matched hybrid Al^(3+)/Zn^(2+)aqueous electrolyte,our phasetransition-free cubic Ti-WO_(3)exhibits an ultra-high cycling stability(>20000 cycles),fast response speed(3,95 s/4,65 s for bleaching/coloring),as well as excellent discharge areal capacity of 214.5 mA h m^(-2),We further fabricate a fully complementa ry aqueous electrochromic device,for the first time,using a Ti-WO_(3)/Prussian blue device architecture.Remarkably,the complementary ECB shows>10000 stable operation cycles,attesting to the feasibility of our Ti-WO_(3)for practical applications.Our work validates the significance of inhibiting the phase transitions of WO_(3)during the electrochromic process for realizing highly cyclable aqueous ECB,which can possibly provide a generalized design guidance for other high-quality metallic oxides for electrochemical applications.

Preparation and electrochromism of pyrochlore-type tungsten oxide film

Pyrochlore-type WO3 powder was synthesized via hydrothermal method using aqueous sodium tungstate solution and oxalic acid as raw materials. The as-prepared powder was made into a soliquoid, from which films were made by dip coating process with indium-tin oxide （ITO）. The obtained films were characterized by thermogravimetric and differential thermal analysis （TG-DTA）, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, cyclic voltammetry （CV）, chronoamperometry （CA） and ultraviolet- visible （UV-Vis） absorption. Results show that the crystal of the pyrochlore-type WO3 powder is perfect. When the calcination temperature rises from room temperature to 500℃, the pyrochlore-type structure first becomes deformed, then it is destroyed and turns into amorphous phase, finally it will completely convert to WO3 with a monoclinic structure. Electrochemical and optical tests demonstrate that the film calcined at 300℃ exhibits the best electrochromic performance and has a coloration efficiency of up to 68.5 cm^2-C^-1 at 884 nm.

An Electrochromic Nickel Phosphate Film for Large-Area Smart Window with Ultra-Large Optical Modulation

Exploring materials with high electrochemical activity is of keen interest for electrochemistry-controlled optical and energy storage devices.However,it remains a great challenge for transition metal oxides to meet this feature due to their low electron conductivity and insufficient reaction sites.Here,we propose a type of transition metal phosphate(NiHPO_(4)·3H_(2)O,NHP)by a facile and scalable electrodeposition method,which can achieve the capability of efficient ion accommodation and injection/extraction for electrochromic energy storage applications.Specifically,the NHP film with an ultra-high transmittance(approach to 100%)achieves a large optical modulation(90.8%at 500 nm),high coloration efficiency(75.4 cm^(2)C^(-1)at 500 nm),and a high specific capacity of 47.8 mAh g^(-1)at 0.4 A g^(-1).Furthermore,the transformation mechanism of NHP upon electrochemical reaction is systematically elucidated using in situ and ex situ techniques.Ultimately,a large-area electrochromic smart window with 100 cm^(2)is constructed based on the NHP electrode,displaying superior electrochromic energy storage performance in regulating natural light and storing electrical charges.Our findings may open up new strategies for developing advanced electrochromic energy storage materials and smart windows.

Sol-gel-based porous Ti-doped tungsten oxide films for high-performance dual-band electrochromic smart windows

Dual-band electrochromic smart windows(DESWs)with independent control of the transmittance of near-infrared and visible light show great potential in the application of smart and energy-saving buildings.The current strategy for building DESWs is to screen materials for composite or prepare plasmonic nanocrystal films.These rigorous preparation processes seriously limit the further development of DESWs.Herein,we report a facile and effective sol-gel strategy using a foaming agent to achieve porous Ti-doped tungsten oxide film for the high performance of DESWs.The introduction of foaming agent polyvinylpyrrolidone during the film preparation can increase the specific surface area and free carrier concentration of the films and enhance their independent regulation ability of near-infrared electrochromism.As a result,the optimal film shows excellent dual-band electrochromic properties,including high optical modulation(84.9%at 633 nm and 90.3%at 1200 nm),high coloration efficiency(114.9 cm^(2) C^(-1) at 633 nm and 420.3 cm^(2) C^(-1) at 1200 nm),quick switching time,excellent bistability,and good cycle stability(the transmittance modulation losses at 633 and 1200 nm were 11%and 3.5%respectively after 1000 cycles).A demonstrated DESW fabricated by the sol-gel film showed effective management of heat and light of sunlight.This study represents a significant advance in the preparation of dual-band electrochromic films,which will shed new light on advancing electrochromic technology for future energy-saving smart buildings.

An overview of recent progress in the development of flexible electrochromic devices

Electrochromic materials are capable of reversibly switching their colors or optical properties through redox reactions under applied voltages,which have shown great potential applications including smart windows,nonemissive displays,optical filters,among others.Although the current rigid electrochromic devices have shown emerging interest and developed rapidly,many applications(e.g.,wearable/deformable optoelectronics)are blocked due to their inflexible features.Herein,the adaption of rigid electrochromic devices to flexible ones is of particular interest for the new era of smart optoelectronics.In this review,the current state-of-the-art achievements of flexible electrochromic devices(FECDs)are highlighted,along with their design strategies and the choice of electrochromic materials.The recent research progress of FECDs is reviewed in detail,and the challenges and corresponding solutions for real-world applications of FECDs are discussed.Furthermore,we summarize the basic fabrication strategies of FECDs and their potential applications.In addition,the development trend,the perspectives,and the outlook of FECDs are discussed at the end of this Review,which may provide recommendations and potential directions to advance the practical applications of FECDs.

Electrochromic-Induced Rechargeable Aqueous Batteries: An Integrated Multifunctional System for Cross-Domain Applications

Multifunctional electrochromic-induced rechargeable aqueous batteries(MERABs) integrate electrochromism and aqueous ion batteries into one platform, which is able to deliver the conversion and storage of photo-thermal-electrochemical sources.Aqueous ion batteries compensate for the drawbacks of slow kinetic reactions and unsatisfied storage capacities of electrochromic devices. On the other hand, electrochromic technology can enable dynamically regulation of solar light and heat radiation. However,MERABs still face several technical issues, including a trade-off between electrochromic and electrochemical performance, low conversion efficiency and poor service life. In this connection, novel device configuration and electrode materials, and an optimized compatibility need to be considered for multidisciplinary applications. In this review,the unique advantages, key challenges and advanced applications are elucidated in a timely and comprehensive manner. Firstly, the prerequisites for effective integration of the working mechanism and device configuration, as well as the choice of electrode materials are examined. Secondly, the latest advances in the applications of MERABs are discussed, including wearable, self-powered, integrated systems and multisystem conversion. Finally, perspectives on the current challenges and future development are outlined, highlighting the giant leap required from laboratory prototypes to large-scale production and eventual commercialization.