By dynamically managing light and heat, electrochromic smart windows (EC-SWs) could improve energy efficiency, occupant comfort, and sustainability, resulting in more energy-efficient and environmentally friendly buildings. However, the external power-driven or solar cell-integrated EC-SW could not fulfill the modern zero energy building purpose. Although recently self-powered EC-SW windows have been invented, their low transmittance modulation and slow response time make them unsuitable for industrial use. In this study, we reported a highly efficient, simple design, and low-cost WO3 self-powered EC window using a roll-to-roll (R2R) slot-die wet coating method where the transmittance modulation is approximately 80% at 600 nm wavelength and the spontaneous recovery time of about 60 s. The device provides around 1.2 V open circuit voltage, which is enough to power up the device itself, and thereby offers a self-powered and fast response EC-SW with high optical modulation.

The development of energy‐efficient window technology is crucial for zero‐energy building approaches, as windows play a pivotal role in minimizing heat loss, optimizing natural light utilization, and contributing to overall energy conservation. In this study, a self‐powered electrochromic smart window is presented together and its application as a self‐charging battery is showcased. The self‐powered system is composed of a WO x electrochromic working electrode, an Al counter electrode, and an AlCl 3 liquid electrolyte similar to a voltaic cell. This device generates an open circuit voltage of around 0.95 V. When two electrodes are connected, this voltage is applied as an external voltage and changes the color of the transparent WO x electrode into a blue state with approximately 62% transmittance modulation. However, if the two electrodes are connected via an light‐emitting diode (LED), the LED lights up for up to 4 h.

For zero-energy buildings, electrochromic smart windows are one of the most essential components, but the external power demand makes this purpose ambiguous. Here, we report a self-powered electrochromic smart window (ECSW) operated by internal electrochemical voltage (chromoVolt). This WO3-based ECSW provides a unique structured device as the 2 mm width Al strip (counter electrode) is placed at one side, making the total window transparent from the front or back point. The WO3 working electrode was fabricated by the large-scale roll-to-roll (R2R) slot-die wet coating method. This device goes into coloured (blue) or bleached (transparent) states spontaneously simply by connecting and disconnecting WO3 and Al electrodes respectively. Going into a deep blue stable-colored state takes approximately 2 min and shows a maximum 56.5 % transmittance change at 600 nm wavelength. Also, this ECSW can provide output potential through internal chemical reactions in a transparent state and can be charged up through disconnection: a self-rechargeable transparent battery application. Three small cells of an active area of 30 mm × 15 mm each provide an output voltage of around 3 V and can power up a small white LED light for up to 1 h. All these phenomena make this electrochromic smart window perfect for a zero-energy building.

Reversible electrodeposition (RED) devices exhibit both transparent and mirror states, allowing light penetration and reflection. Therefore, the incident light transmission regulates the radiant heat generation. However, the low bistability of these devices is the main limitation to their application in windows since it causes continue energy consumption to maintain the mirror state; this is mainly due to the presence of Cu ions in the electrolyte, which is the main dissolution agent of the deposited Ag metal. Thus, we used a three-layered TiO2 counter electrode as an electrochemical reaction mediator and eliminated the Cu ions. In addition, the Ag thin film pre-deposited on the working electrode effectively enhanced the bistability. The combination of three-layered TiO2 and the pre-deposited Ag film allowed a reflectance of 78% and enhanced the mirror-state maintenance of the mirror state. After switching off the voltage, the retained reflectance was 17% at three-layered TiO2 more than twice larger than that at one-layered TiO2 (7%). The bistability and reflectance increase in the proposed RED devices with respect to those based on a Cu-containing electrolyte.

Long-lived electrochromic devices (ECDs) with multilevel bistability based on a portable film-type polymer electrolyte (PFPE) were fabricated and their optical and electrical properties were characterized. WO3 and NiOx, deposited via a vacuum method, were used as electrochromic materials, and PFPEs were assembled in ECDs by a transfer method. The PFPEs were fabricated by inserting a polyvinyl acetal (PVA) based gel electrolyte between a light and a tight release films. The PFPE-based ECD operated reliably for at least 109,000 cycles and showed excellent bistability in multilevel open circuits. For 30 min after removing the applied operating voltage, the ECD maintained 90% and 99% of the original coloration and decoloration transmittance at 550 nm, respectively. The average coloration and decoloration consumed charge and efficiency over 109,000 operation cycles were 4.2 and -4.5 mC/cm(2) and 81.4 and -74.8 cm(2)/C, respectively.

Electrochromic materials and devices have attracted much attention with their ability to tune the transmissions of visible to infrared (IR) light, allowing the creation of smart windows. This study presents a novel electrochromic device (ECD)‐based photonic device that can modulate IR light intensity in a planar optical waveguide ECD. To configure it, a multilayer ECD made of WO 3 is integrated on a polymer optical waveguide platform. By using the waveguide to change the optical properties of the ECD electrically, IR light propagating along the optical waveguide core undergoes electroabsorption loss due to the change in charge carrier density in WO 3 layer and its intensity is modulated with an extinction depth of 0.6 dB mm −1 . Experimental results show that the device is capable of discrete intensity attenuation by applying a distinct level gate voltage. Periodic application of gate voltage leads the device to serve as an optical modulator on the order of subseconds. The results also confirm that a new approach to consider ECD‐based optical modulators can pave the way for the development of planar photonic‐integrated circuits and systems.

A new switchable holographic device concept using reversible electrodeposition (RED) technology is proposed. The proposed device has a structure in which the cavity structure is changed by the reversible deposition of Ag, and thus the characteristics of the reflected light are modulated. It has a high reflectance due to a mirror reflection structure and exhibits phase modulation by the reversible deposition of Ag. Because the proposed device is a current-driven device, it is expected to overcome the limitation in the scaling down of the pitch in spatial light modulators, which is considered a limitation of liquid crystal device. A passive type switchable holographic device with a 1 mu m pitch is implemented using the proposed device. The successful implementation of a switchable holographic image using the fabricated device is confirmed. The proposed device is expected to be applicable as an active metasurface and spatial light modulator device in the visible light region in the future because it has a large modulation in the visible light region.

For environmental reason, buildings increasingly install smart windows, which can dim incoming daylight based on active electrochromic devices (ECDs). In this work, multi-layered graphene (MLG) was investigated as an ECD window electrode, to minimize carbon dioxide (CO2) emissions by decreasing the electricity consumption for building space cooling and heating and as an alternative to the transparent conductor tin-doped indium oxide (ITO) in order to decrease dependence on it. Various MLG electrodes with different numbers of graphene layers were prepared with environmentally friendly poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) to produce ECD cells. Tests demonstrated the reproducibility and uniformity in optical performance, as well as the flexibility of the ECD fabrication. With the optimized MLG electrode, the ECD cells exhibited a very fast switching response for optical changes from transparent to dark states of a few hundred msec.

A new structure for a switchable mirror device based on reversible electrodeposition is proposed. This device does not contain Cu ions in the electrolyte and adapts a counter electrode. The feasibility of the device was evaluated with a WO3 film, which is a well-known electrochromic material, as a counter electrode. Even in the absence of Cu ions, the WO3 film facilitates a clean erase feature in the device. Furthermore, using a pre-deposited Ag film as a working electrode, Ag deposition can be driven at a substantially lower voltage than that in conventional devices. Moreover the deposition current decreases with the progress of Ag deposition, and stops after completion of the deposition process. The results clearly indicate that the tri-bromine ion, which makes the self-erasing circulation, is not generated during Ag deposition process. The new switchable mirror shows excellent bistability and size scale-up is possible because it does not consume continuous current in the mirror state. By appling the proposed technology, a switchable mirror device with a 7 cm × 9 cm active area was successfully fabricated.

A new inorganic–organic hybrid electrochromic mirror device was fabricated, which is very transparent; its transparency and optical and electrical properties are highly influenced by the structure of the counter electrode (CE). The working electrode (WE) was fabricated via vacuum deposition of Ag, ITO, and WO3 films on glass, in sequence. Ag, ITO, and WO3 served as mirror and low resistance electrode, Ag protective layer, and inorganic reduction electrochromic layer, respectively. This study used a flat CE and nanoporous structured CE that had greatly increased surface to volume ratio. Flat CE did not reduce portion of oxidized phenothiazine (PH). In decoloration state, mirror device still had reddish color; this was a factor that decreased the decoloration reflectance. On the other hand, the use of nanoporous structured CE reduced the entire amount of oxidized PH, completely eliminated the reddish color, and enabled the fabrication of highly reflective mirror devices. Moreover, the use of nanoporous structured CE improved the electrochromic optical and electrical properties, leading to high reflectance variation, low consumed charge, low coloration static current, and fast response time compared to those characteristics of flat CE.

As potential lighting-emitting devices, electrochemiluminescence (ECL) devices are promising in terms of device structure and fabrication and involve low processing cost compared to organic light-emitting devices (OLEDs).

Magneto-/electro-chromatic reflective color tunability is confirmed using hydrophobic surface modified magnetite nanoparticles. The optical reflective color spectra and color gamut demonstrate the promising applications in reflective displays.

The development of digital holography is anticipated for the viewing of 3D images by reconstructing both the amplitude and phase information of the object. Compared to analog holograms written by a laser interference, digital hologram technology has the potential to realize a moving 3D image using a spatial light modulator. However, to ensure a high-resolution 3D image with a large viewing angle, the hologram panel requires a near-wavelength scale pixel pitch with a sufficient large numbers of pixels. In this manuscript, we demonstrate a digital hologram panel based on a chalcogenide phase-change material (PCM) which has a pixel pitch of 1 μm and a panel size of 1.6 × 1.6 cm 2 . A thin film of PCM encapsulated by dielectric layers can be used for the hologram panel by means of excimer laser lithography. By tuning the thicknesses of upper and lower dielectric layers, a color-selective diffraction panel is demonstrated since a thin film resonance caused by dielectric can affect to the absorption and diffraction spectrum of the proposed hologram panel. We also show reflection color of a small active region (1 μm × 4 μm) made by ultra-thin PCM layer can be electrically changed.

Light-adaptable (LA) displays combining the advantages of reflective and emissive displays, are considered as the future of display technology. Electrochromic devices are potentially strong candidates for reflective-mode LA displays because of their high transmittance in the transparent state and low power consumption. However, the narrow viewing angle of these displays in relation to a hybrid structure of the LA display, is a technical barrier that must be overcome for the successful application of electrochromic devices to light-adaptable displays. In the present study, an electrochromic device with a self-diffusing function was developed for application to light adaptable displays. Si3N4 scattering particles were incorporated in the TiO2 nanostructure-based electrochromic device. Efficient forward diffuse scatterings were obtained without deteriorating the total transmittance of the device. The contrast ratio and color gamut of the electrochromic device were dramatically improved because of the addition of the scattering particles.

In order to provide stimuli-responsive properties under magneticand electric-forces enabling reflective color-changes in a liquid medium, the surface of silica coated-iron oxide core–shell nanoparticles (Fe3O4@SiO2) is successfully modified with two-different types of silane coupling agents to improve the dispersion stability as well as the color change strength as a result of the effectively increased repulsion. A stimuli-responsive magnetoand electro-chromatic ink is prepared by mixing hydrophobic surface modified Fe3O4@SiO2-Fx (x 1⁄4 0 and 13) core–shell nanoparticles and a dispersing agent in a low dielectric medium (LDM). The magneto-chromatic and electro-chromatic stimuli-responsive properties are visually confirmed. Moreover, the optical reflective color spectra and color gamut calculated from the CIE chromaticity coordinates of the hydrophobic surface modified Fe3O4@SiO2-F13 core–shell nanoparticles (with “F moiety” in the molecular structure) under an applied voltage range of 0 V to 10 V show that the hydrophobic surface modified magnetite nanoparticles are promising candidates for reflective display applications.

A Fabry-Perot type integrated color reflector, with red/blue/green colors as subpixels, was designed and fabricated with Si substrate. Ag films were used as reflective mirror layers, SiO2 films were used as Fabry-Perot cavity layers and W films were used as partially reflective layers for the cavity. To minimize the effects of the thickness variation of the oxide cavity layers, the structure of the color reflector was optimized, and the differential deposition scheme was devised and applied in the fabrication process. The integrated color reflector was successfully fabricated with the proposed fabrication scheme. The measured white reflectance was > 45% in the visible spectrum range and -49% at 550 nm wavelength. The fabricated reflector had moderate color gamut of 17% of the National Television System Committee (NTSC) standard and it showed very high white reflectivity. The fabricated color reflector is expected to be applicable to reflective displays.

Electrochromic (EC) phenomena are that their optical transmittance and/or reflectance change because of chemical reduction/oxidation processes occurred by the ions insertion and extraction when a potential is externally applied. In order to increase the ratio and speed of chemical reduction/oxidation processes, which are essential required property, there are many efforts to prepare the ionic conductors based on such as organic-solvents/liquids, ionic liquids, and polymer/gel. Although organic-solvent/liquid based ion conductors show better physical properties likely lower viscosity, density, and melting point helps easier ion mobility in medium, they exhibit low stability, high flammability, and low safety which limit the promising wide range application of EC devices (ECDs). Therefore instead of using organic-solvent/liquid based ion conductors, ionic liquids (ILs) are considered because of non-volatility, possibly makes choice and/or certainly increasing ion concentration, etc. In spite of these advantages, polymer and/or gel-typed ion conductors are only suitable in terms of the flexibility and scalability of ECDs. As their visco-elastic properties, polymer/gel-based ion conductors afford guaranteed good contact with the electrodes, and they also have simple processablity resulted in low production cost and better mechanical properties along with improved stability, reliability, and safety. Therefore, in the present work, polymer-based ion conductor is prepared and is optimized in order to obtain the efficient contrast ratio and switching speed for ECDs. In order to see the feasibility, the operation of polymer-based ion conductor introduced ECD fabricated on flexible substrate will be also presented. Acknowledgement This work was supported by Institute for Information & communications Technology Promotion (IITP) grant funded by the Korea government (MSIP) (B0101-16-0133, The core technology development of light and space adaptable energy-saving I/O platform for future advertising service).

Electrochromic devices (ECDs) having a high switching speed and a good durability were developed with viologen-anchored TiO2 (VTO) nanoparticles and antimony-doped SnO2 (ATO) nanoparticles. The fabricated ECDs showed a good stability after 30,000 cycles driving at 4Hz speed. Also, the dynamic behavior of their devices was studied using 6×6 patterned array cells. The driving tests of 4 types were used to understand the exact driving mechanism and to prevent the rapid blur problem.

The optical and electrical properties of electrochromic devices (ECDs) have been studied as a function of the electrolyte concentration and the cell gap. During tests, the electrolyte concentration was adjusted from 0.01 to 1 M LiClO 4 , and the cell gaps between the positive and negative electrodes were set at 25, 60, and 100 µm. By varying the electrolyte concentrations and the cell gap, various parameters such as the transmittance, response time, charge consumption, coloration efficiency, and bistability of ECD were comparatively analyzed. Viologen (VO) was used as the reduction electrochromic material, and triarylamine (TAA) was used as the oxidation material.

In this paper, we investigate the effects of pre-reducing Sb-doped SnO2 (ATO) electrodes in viologen-anchored TiO2 (VTO) nanostructure–based electrochromic devices. We find that by pre-reducing an ATO electrode, the operating voltage of a VTO nanostructure–based electrochromic device can be lowered; consequently, such a device can be operated more stably with less hysteresis. Further, we find that a pre-reduction of the ATO electrode does not affect the coloration efficiency of such a device. The aforementioned effects of a pre-reduction are attributed to the fact that a pre-reduced ATO electrode is more compatible with a VTO nanostructure–based electrochromic device than a non-pre-reduced ATO electrode, because of the initial oxidized state of the other electrode of the device, that is, a VTO nanostructure–based electrode. The oxidation state of a pre-reduced ATO electrode plays a very important role in the operation of a VTO nanostructure–based electrochromic device because it strongly influences charge movement during electrochromic switching.