Li-Ion-Trapping-Induced Degradation Mechanism of Colored State in Tungsten Oxide Electrochromic Films

Aiming to investigate the degradation mechanism of their colored states, tungsten oxide films with different oxygen/tungsten ratio were prepared by direct current reactive magnetron sputtering through adjusting the oxygen partial pressure. After a long-term cycling test, the sample prepared under low oxygen partial pressure (LO#) showed an excellent cycle stability which its optical modulation amplitude remains stable at 23.6%, while the one prepared under high oxygen partial pressure (HO#) exhibited an obvious degradation process of the colored state, leading to the optical modulation amplitude decreased from 34.0% to 18.6% accompanied with a decay of ionic diffusion coefficient and electrode potential, but having an improved coloration efficiency. Combined with various structural characterizations, including SEM, LA-ICP-MS, Raman and XPS, we demonstrate such colored state degradation is attributed to the so-called shallow trap, which corresponds to the irreversible and non-coloring reaction with interstitial oxygen during the insertion of Li+ cations forming superoxides (e.g. LiO2). All these findings not only offer a new insight into the improvement of cyclic stability based on ion-exchange, but also provide a valued information to understanding the physicochemical mechanisms of degradation in electrochromic materials.

A study of the possibility of conducting selective laser processing of thin composite electrochromic Ni(OH)2-PVA films

The surfaces of thin composite electrochromic Ni(OH)2-polyvinyl alcohol films, deposited by the cathodic template method on FTO glass substrates, were proposed to be processed using laser radiation. The processing of these films was carried out in a colored state with a laser beam of a semiconductor emitter with a wavelength of 650 nm (red) with a pulse duration of 3,000 μs, the beam diameter was about 40 μm. The energy at a single point was 37.5 J/cm2. The result was a film with microholes of about 80 μm. The transparent areas of the surface did not exhibit electrochromic properties, which indicated the absence of the original electrochromic coating. The study of the properties of the laser-processed film following a certain pattern showed that the characteristics of composite Ni(OH)2-polyvinyl alcohol coatings had changed significantly. On the one hand, the coloration depth of the films decreased by several percent, on the other hand, the specific electrochemical characteristics increased significantly. The study also showed that laser processing did not lead to significant changes in the main properties of the transparent electrically conductive layer – color and resistance. Before and after laser processing, the surface resistance of FTO glasses was 12.1±0.9 and 14.4±1.2 Ohm/sq., respectively. In addition, it was found that the processing of Ni(OH)2-polyvinyl alcohol films improved the adhesion of the latter to the surface of FTO glass. Based on the data obtained, a selective method was proposed for modifying thin colored films deposited on transparent conductive oxides (FTO, ITO, AZO) by visible laser radiation. This approach to changing the properties of films can be useful for areas related to the development of sensors, microelectronics, solar cells, small-sized current sources, electrodes with high efficiency, etc.

Automatic light-adjusting electrochromic device powered by perovskite solar cell

Electrochromic devices can modulate their light absorption under a small driving voltage, but the requirement for external electrical supplies causes response-lag. To address this problem, self-powered electrochromic devices have been studied recently. However, insensitivity to the surrounding light and unsatisfactory stability of electrochromic devices have hindered their critical applications. Herein, novel perovskite solar cell-powered all-in-one gel electrochromic devices have been assembled and studied in order to achieve automatic light adjustment. Two alkynyl-containing viologen derivatives are synthesized as electrochromic materials, the devices with very high stability (up to 70000 cycles) serves as the energy storage and smart window, while the perovskite solar cell with power-conversion-efficiency up to 18.3% serves as the light detector and power harvester. The combined devices can automatically switch between bleached and colored state to adjust light absorption with variable surrounding light intensity in real-time swiftly, which establish significant potentials for applications as modern all-day intelligent windows.

Electrosynthesis of Electrochromic Polymer Membranes Based on 3,6-Di(2-thienyl)carbazole and Thiophene Derivatives

Five carbazole-containing polymeric membranes (PDTC, P(DTC-co-BTP), P(DTC-co-BTP2), P(DTC-co-TF), and P(DTC-co-TF2)) were electrodeposited on transparent conductive electrodes. P(DTC-co-BTP2) shows a high ΔT (68.4%) at 855 nm. The multichromic properties of P(DTC-co-TF2) membrane range between dark yellow, yellowish-green, gunmetal gray, and dark gray in various reduced and oxidized states. Polymer-based organic electrochromic devices are assembled using 2,2′-bithiophene- and 2-(2-thienyl)furan-based copolymers as anodic membranes, and poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) (PEDOT-PSS) as the cathodic membrane. P(DTC-co-TF)/PEDOT-PSS electrochromic device (ECD) displays a high transmittance change (ΔT%) (43.4%) at 627 nm as well as a rapid switching time (less than 0.6 s) from a colored to a bleached state. Moreover, P(DTC-co-TF2)/PEDOT-PSS ECD shows satisfactory optical memory (the transmittance change is less than 2.9% in the colored state) and high coloration efficiency (512.6 cm2 C−1) at 627 nm.

Effect of Sputtering Power on Optical Properties of Nickel Oxide Electrochromic Thin Films

The preparation and characterization of nickel oxide (NiO) thin film for electrochromic smart window applications are studied. The NiO thin film was prepared by the DC magnetron sputtering from a pure nickel target. The sputtering power was varies in the interval 50–200 W. The crystallinity and physical morphology of NiO films are characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. The XRD result revealed that polycrystalline NiO thin films with preferred growth directions along (111) and (200) planes are obtained. Moreover, the electrochromic property of NiO thin films was investigated with a UV-Visible spectrophotometer. The colored state of the electrochromic cell was obtained by the ion insertion at the 1-V external applied bias in 0.1 M KOH. The reversibility between the colored and bleached states is confirmed by the optical transmittance. The result shows the optical contrast as high as 28.68.

Optical properties of doping electrochromic M0.125W0.875O3 (M=Mo, Nb, Ta, Ti, V): A first-principles study

Tungsten trioxide (WO3) is a representative electrochromic material that can change their optical properties under the action of a voltage pulse and has attracted great interest in the applications of energy efficient windows. Models of various W0.125M0.875O3 and LixM0.125W0.875O3 (M=Mo, Nb, Ta, Ti, V) were built to simulate the bleached and colored state of WO3 materials by first-principles calculations, respectively. The calculations show that doping systems of LixM0.125W0.875O3 (M= Nb, Ta, V) lead to an enhancement of the modulation efficiency in invisible light and a decrease in the modulation efficiency in near infrared region (NIR). Ti doping boosts an excellent high efficiency of NIR modulation, while no modulation was observed in the visible light region. Mo doping remarkably promotes the coloration efficiency in both NIR and visible regions. The specific characteristics of doped WO3 systems deserve more exploration of their application in green house or thermal modulation smart window.

Effect of Cell Thickness on the Electro-optic Response of Polymer Stabilized Cholesteric Liquid Crystals with Negative Dielectric Anisotropy

It has previously been shown that for polymer-stabilized cholesteric liquid crystals (PSCLCs) with negative dielectric anisotropy, the position and bandwidth of the selective reflection notch can be controlled by a direct-current (DC) electric field. The field-induced deformation of the polymer network that stabilizes the devices is mediated by ionic charges trapped in or near the polymer. A unique and reversible electro-optic response is reported here for relatively thin films (≤5 μm). Increasing the DC field strength redshifts the reflection notch to longer wavelength until the reflection disappears at high DC fields. The extent of the tuning range is dependent on the cell thickness. The transition from the reflective to the clear state is due to the electrically controlled, chirped pitch across the small cell gap and not to the field-induced reorientation of the liquid crystal molecules themselves. The transition is reversible. By adjusting the DC field strength, various reflection wavelengths can be addressed from either a different reflective (colored) state at 0 V or a transparent state at a high DC field. Relatively fast responses (~50 ms rise times and ~200 ms fall times) are observed for these thin PSCLCs.

Electrochromic properties of Mo-doped V2O5 thin films deposited by spray pyrolysis process

In this work, we have studied the Mo effect on V2O5 thin films, the samples were deposited by spray pyrolysis technique on heated glass substrates at 500 °C. The dopant amount was varied at different concentration, 2%, 4% and 6%. Different techniques were carried out, in order to studied the Mo effect on V2O5, such as XRD, Raman, SEM, AFM and electrochemical analysis. From the obtained results, all the samples exhibited orthorhombic structure with (001) predominant orientation. The optical properties of Mo concentration effect were studied in their colored and discolored states. These electrochemical studies were performed in LiClO4 electrolyte with 0.5 mol/L of C4H6O3. The transmittance value of the samples decreased from 76% to 10% at 690 nm, when the samples have changed color, from colored state to discolored state respectively.