Optimized properties of innovative ElectroChromic Device using ITO / Ag / ITO electrodes

The “Dielectric/Metal/Dielectric” (DMD) stacked films being used as transparent and conductive (TC) electrodes, have demonstrated excellent application in the ElectroChromic (EC) process and devices. In this work, multilayers (IAI) made of 50 nm of Indium Tin Oxide (ITO)/5 nm of metallic silver (Ag)/30 nm of ITO that exhibit band-gap, low resistance of 7.4 Ω and the high figure of merit of 9.9 × 10−3 Ω−1 were introduced in a complete five-layer Glass/IAI/NiOx/LiClO4-PC-PMMA/WO3/IAI/Glass ElectroChromic Device (ECD). The single IAI electrode as well as the two actives EC layers Glass/IAI/NiOx and Glass/IAI/WO3 were firstly characterized for their TC and EC properties respectively. Then, the EC properties of the complete five-layer ECD were analyzed. Fast response time (2.02 s for the bleaching and 2.25 s for complete coloration), wide optical modulation in the visible light region (∼55% at 550 nm), long lifetime (more than 6000 s), large capacity and good stability as well as high coloration efficiency (31.7 cm2 C−1) were obtained. The improved EC performance of ECD were related to the good electrical and optical properties of IAI electrode

Electrolytes-relevant cyclic durability of nickel oxide thin films as an ion-storage layer in an all-solid-state complementary electrochromic device

NiOx thin films approximately 300 nm thick were deposited on indium tin oxide (ITO)-coated glass substrates by magnetron sputtering. Their electrochromic properties were tested in a 1 M potassium hydroxide (KOH) aqueous solution and in a 1 M lithium perchlorate dissolved in propylene carbonate (LiClO4-PC) anhydrous electrolyte, respectively. The evolution of the lattice structure, surface morphology, chemical composition, optical transmittance modulation, cyclic voltammograms, inserted and extracted charge capacities of NiOx thin films was evaluated as a function of the number of cycles. Even though the cyclic voltammograms and the charge capacity present a similar variation tendency during 1000 cycles, significant differences between cycling in 1 M KOH and 1 M LiClO4-PC were observed. In 1 M KOH, X-ray diffraction (XRD) results showed that the lattice planes (111) and (200) had a larger shift toward higher diffraction angles, and SEM images exhibited that cracks emerged more quickly from the surface of NiOx thin film during the cycling process. More importantly, the optical modulation varying from 58.5% to 32.9% presented an obvious degradation after 1000 cycles. On the contrary, in 1 M LiClO4-PC, NiOx thin films presented a better cyclic durability and a stable optical modulation approximating 41%. In a second step, an all-solid-state complementary electrochromic device with an ITO/WO3/LiClO4-PC-PMMA/NiOx/ITO structure was assembled. The device had an average optical modulation of 51.7% in the visible region and an excellent cyclic durability (over 50,000 times). In situ optical transmittance spectra showed that, in the initial cycles, the response time was 4.5 s for the coloring process and 1.7 s for the bleaching process. After 1000 cycles, both were delayed to 5.0 s and 2.9 s, respectively. In addition, open circuit memory of the device was characterized by the optical transmittance variation plotted against time after disconnection of the external circuit.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Charge-transfer kinetics and cyclic properties of inorganic all-solid-state electrochromic device with remarkably improved optical memory

Optical memory effect plays a critical role in energy-saving coefficient of electrochromic devices (ECDs). Due to the finite electron-blocking capacity of ions electrolyte layer and the weak interfacial energy between the ions electrolyte layer and electrochromic layers, typically five-layer inorganic all-solid-state ECDs generally suffer from poor optical memory. A seven-layer inorganic ECD with significantly improved optical memory is designed by means of the embedment of Ta2O5 layers between ions conductive layer and electrochromic layers. Compared with the typical five-layer ECD-1 (ITO/NiOx/LiNbO3/WO3/ITO), the seven-layer ECD-2 with the structure of ITO/NiOx/Ta2O5/LiNbO3/Ta2O5/WO3/ITO presents much less leakage current, larger optical modulation and higher coloration efficiency during electrochemical cycling. The further analyses reveal that the embedded Ta2O5 layers greatly increase the energy barrier between NiOx, WO3 and LiNbO3, imposing restrictions on the transfer kinetics of electrons contributing to the leakage current and enlarging the threshold potential available to ECD-2, which gives rise to a high coloration efficiency up to 98.0 cm2 C−1. Furthermore, the seven-layer ECD-2 maintains a stable optical modulation of approximately 52.5% for over 10,000 cycles, even though there is a compromise in response characteristic due to the Li+-ion trapping in electrochromic layers, which provides a further insight into the electrochromic degradation of inorganic all-solid-state complementary ECDs.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Life-cycling and uncovering cation-trapping evidence of a monolithic inorganic electrochromic device: glass/ITO/WO3/LiTaO3/NiO/ITO

The visualization of the microstructure change and of the depth of lithium transport inside a monolithic ElectroChromic Device (ECD) is realized using an innovative combined approach of Focused Ion Beam (FIB), Secondary Ion Mass Spectrometry (SIMS) and Glow Discharge Optical Emission Spectroscopy (GDOES). The electrochemical and optical properties of the all-thin-film inorganic ECD glass/ITO/WO3/LiTaO3/NiO/ITO, deposited by magnetron sputtering, are measured by cycling voltammetry and in situ transmittance analysis up to 11 270 cycles. A significant degradation corresponding to a decrease in the capacity of 71% after 2500 cycles and of 94% after 11 270 cycles is reported. The depth resolved microstructure evolution within the device, investigated by cross-sectional cutting with FIB, points out a progressive densification of the NiO layer upon cycling. The existence of irreversible Li ion trapping in NiO is illustrated through the comparison of the compositional distribution of the device after various cycles 0, 100, 1000, 5000 and 11 270. SIMS and GDOES depth profiles confirm an increase in the trapped Li content in NiO as the number of cycles increases. Therefore, the combination of lithium trapping and apparent morphological densification evolution in NiO is believed to account for the degradation of the ECD properties upon long term cycling of the ECD

Catalyst-free growth mechanism and structure of graphene-like nanosheets formed by hot-filament CVD

We report on a simple and effective method of synthesizing graphene-like nanosheets on silicon substrates pre-deposited with a carbon film or carbon nanodots in hot-filament(HF)CVD from a methane precursor. The results of field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and micro-Raman spectroscopy (RS) indicate that the structure of graphene-like nanosheets is changed with the flow rate change of methane and the pretreatment of the substrate surface. The catalyst-free growth of graphene-like nanosheets is related to the diffusion and assembly of carbon atoms on the substrate surface and the separation of graphene-like nanosheets from the substrate surface. ? 2014 Wiley-VCH Verlag GmbH & Co. KGaA

Dynamic behaviors of inorganic all-solid-state electrochromic device: Role of potential

Applied potential plays a significant role in the properties of electrochromic devices (ECDs), for example, cyclic property, optical modulation, and response rate. In this study, inorganic all-solid-state ECDs with the multilayer structure of Glass/ITO/NiOx/Ta2O5/LiNbO3/Ta2O5/WO3/ITO were prepared by magnetron sputtering. The potential dependence of charges dynamic behaviors in the ECDs were analyzed on the basis of cyclic voltammograms (CVs), chronoamperograms (CAs), multi-potential steps, and in-situ optical transmittance at 550 nm. Results demonstrated that the trapping of Li+ ions in NiOx layer and in WO3 layer were responsible for the degradation of electrochromic properties of the ECDs operated at different potential ranges. Besides, the dynamic behavior of Li+ ions in WO3 layer, acting as the primary electrochromic layer in the ECDs, had a crucial influence on the response characteristics of the ECDs. Excellent optical memory effects at randomly electrochromic extent were observed and the corresponding open-circuit potential was relevant to the chemical potential of the ECDs.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

In situ electrochromic efficiency of a nickel oxide thin film: Origin of electrochemical process and electrochromic degradation

Electrochromic nickel oxide (NiOx) thin films are one of the most promising anodic colored materials. However, there is lack of accurate description of their electrochemical process and degradation mechanism. In this study, a novel approach involving in situ electrochromic efficiency is proposed to reveal the electrochemical origin of an electrochromic NiOx thin film cycled in a Li+-ion electrolyte. The results indicate that the coloring process of the NiOx thin film refers to the oxidation reactions of Ni2+ to Ni3+ and Ni2+ to Ni4+ (in two forms of Ni3O4 and Ni2O3), and the bleaching process is associated with the reduction reactions of Ni4+ to Ni2+, Ni4+ to Ni3+, and Ni3+ to Ni2+. The irreversible reduction of Ni4+ to Ni3+ plays a dominant role in the activation procedure of NiOx. It is deduced that the Li+-ion trapping in the bleaching process along with the reduction reactions of Ni4+ to Ni3+ and Ni3+ to Ni2+ causes the degradation of the electrochromic properties. This study provides a further insight into the electrochromic mechanism and is conducive to the improvement of the long-term cyclic durability for Li+-based electrochromic NiOx. Moreover, the study significantly establishes a direct connection between an electrochemical process and a variation in the optical absorbance of materials.SCOPUS: ar.jinfo:eu-repo/semantics/publishe