Our e-connected society is eager to develop devices with tunable colors. Electrochromic materials, able to modify their optical properties under an applied voltage, offer a smart solution. In the ...present study, we have successfully synthesized two vanadium oxide powders from a polyol-mediated synthesis, and powder suspensions were coated on glass/ITO substrates by doctor blading. The electrochemical and optical properties of the V x O y films are investigated by cyclic voltammetry (CV) coupled with in situ UV–visible spectroscopy. Both V2O5 and V2O3 films exhibit reasonably good cycling stability, significant reflectance modulation, high optical contrast, and good memory effects revealing the unknown EC properties of V2O3. The similar green ⇄ blue ⇄ orange reversible color changes for both vanadium oxides appear suitable for display application. Then, the evolution of the vanadium cation oxidation states and of the structure of V2O5 and V2O3 upon cycling are analyzed by ex situ XPS and ex situ XRD (at grazing incident angle). This work highlights a robust and novel scenario upon cycling, nearly the same whatever the raw film composition that shows, for each cycle, the crystallization of V2O5 upon oxidation, followed by amorphization upon reduction.
A V2O5 film fabricated by a nanoparticle deposition system (NPDS) was used to demonstrate a highly durable electrochromic device (ECD). The V2O5 film deposited on both the electrodes functioned as a ...complementary layer during the redox reaction to balance the charge inside the device. Thereby, it mitigated the load applied to the ECD by enabling its electrochromic reaction within the range of ±1 V. The fabricated ECD showing different colors at opposite voltages were applied to both the electrodes. Meanwhile, a TiO2-based opaque electrolyte was used to show different colors of V2O5 thin films independently. The fabricated ECD can display three colors: yellow, green, and blue. Furthermore, each color variation is completed within 10 s. According to the International Commission on Illumination (CIE) data, the color differences (ΔE) between yellow and green, green and blue, and yellow and blue were measured to be approximately 27, 17, and 44, respectively. Meanwhile, the fabricated ECD showed almost a similar level of electrochromic performance even after 500 repeated runs. Moreover, the charge capacity of the ECD after a 10,000-cycle cyclic voltammetry (CV) analysis was 49.01 mC/cm2 (the initial charge capacity was measured to be 47.31 mC/cm2). This verified the high durability of the device. Thus, an ECD capable of coloration under a low voltage range of ±1 V was fabricated using a dry deposition method with a TiO2-based opaque electrolyte, to vividly display different colors at both sides of the device simultaneously. The unique device can independently display different colors on both the electrodes. The dry deposition method was applied to deposit an identical V2O5 electrochromic film on the electrodes and an opaque electrolyte. The device has potential applications in functional electrochromic displays.
•V2O5 film fabricated by nanoparticle dry deposition system was used to fabricate ECD.•Electrochemical durability of V2O5 based ECD was shown up to 10,000 Cycles.•The two electrochromic films were visually separated using an opaque gel electrolyte.•Coloration voltage of the device is reduced under a low voltage range of ±1 V.•Different colors were shown vividly at both sides of the device simultaneously.
In this work, the electrochromic and structural properties of NiO thin films prepared using optimized low value electrodeposition parameters were studied. The optimized parameters were deposition ...current density, molar concentration of nickel nitrate solution, and deposited charge density. The highest electrochromic characteristics corresponded to deposition parameters of −0.05 mA/cm2 deposition current density, 0.02 M of Ni(NO3)2.6H2O solution, and charge density of 80 mC/cm2. For this optimized film, at 630 nm wavelength, the transmittance modulation ΔT was 76%, the efficiency η was 19 cm2/C, the charge reversibility Qc/Qa was 97%, and a remarkable contrast ratio CR of 5.9. In addition, a good cycling stability was confirmed up to 900 cycles. Optimized NiO thin films were poorly crystallized exhibiting a nano-flake structure, high porosity, and homogeneity.
•Low value electrodeposition parameters were used to prepare optimized NiO electrochromic film.•Optimized deposition parameters are Jd = -0.05 mA/cm2 , 0.02 M of Ni(NO3)2.6H2O solution, and charge density of 80 mC/cm2•Optimized film has ΔT of 76 %, efficiency η was 19 cm2/C, Qc/Qa was 97%, CR of 5.88, and cycling stability up to 900 cycles.•Optimized NiO thin films were poorly crystallized exhibiting a nano-flake structure, high porosity, and homogeneity.
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/WO
3
/LiTaO
3
/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.
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 switching time is one of the key parameters used to assess the performance of an electrochromic material or device. In spite of its importance, there is currently no standard for how this ...parameter is defined, and as a result, it is difficult to compare switching time data between different research groups, and to quantify and assess reported improvements. We propose a standard method for reporting electrochromic switching times, based on straightforward experimental fittings resulting in an analytical expression that can directly correlate obtainable optical contrast values with their corresponding switching times. This analytical expression makes it possible to unambiguously define the performance of an electrochromic material or device using two parameters: a full-switch contrast and a time constant.
•A standard method to unambiguously define electrochromic switching time is presented.•An exponential function correlates contrast with the time needed to obtain it.•Full-switch contrast and time constant unequivocally define the switching process.•The method is valid regardless the materials nature and experimental conditions.
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.
Nickel oxide thin films were deposited by sol-gel combined with spin coating method. Herein, the influence of the concentration of the precursor, kind of solvents, stabilizers and type of final ...treatment (calcination or UV treatment) on the structural, morphological, and electrochromic properties of NiO thin films is reported. Enhanced electrochromic properties, corresponding to a modulation of the optical transmittance upon an applied voltage, are established for NiO thin films prepared with methanol as solvent, Triton X-100 as stabilizer and treated by UV using a lamp with low power of 30 W for 5 h. These findings highlight the benefit of using UV treatment, as replacement of annealing step for enhanced NiO electrochromic properties.
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•Nickel oxide thin films were deposited by sol-gel combined with spin coating method.•Enhancement of electrochromic properties of NiO thin films by UV treatment.•High optical contrast for UV-treated (30 W for 5 h) NiO thin films prepared using methanol and triton X-100.
Des couches minces d'oxyde de vanadium, V2O5, ont été déposées à température ambiante sur substrat ITO/verre en utilisant trois conditions de dépôt différentes, à savoir la pulvérisation cathodique ...par magnétron haute fréquence (RFMS) avec cible métallique en V (métal V2O5RF) et cible d’oxyde de V2O5 (oxyde V2O5RF) et la pulvérisation cathodique par magnétron en régime d’impulsions de haute puissance (HiPIMS) avec cible métallique (V2O5HiPIMS), respectivement. L’optimisation des différents paramètres de dépôt conduit à une modulation de la structure et morphologie des films, d’amorphes à cristallisés et de denses à poreux. Le cyclage en milieu lithié ou sodé montre un multichromisme associé à un changement réversible de coloration impliquant 4 couleurs, orange, vert, bleu et gris, en fonction des états de réduction et d’oxydation. Un cyclage prolongé sur 1000 CV, indique une différence de stabilité en fonction de la méthode de dépôt. Les films denses déposés par HiPIMS présentent une grande stabilité tandis qu’une dégradation très rapide est observée pour les films amorphes (oxyde V2O5RF) et qu’une augmentation de capacité est observée pour les films (métal V2O5RF). Ces différences de comportement sont attribuables à des différences de morphologie faisant apparaitre des films fissurés et fragiles dans un cas et denses sans grande évolution dans l’autre cas. Par ailleurs, le cyclage longue durée entraine une amorphisation des films. La caractérisation par un grand nombre de techniques (GIXRD, XPS, TOF-SIMS, AES et RBS / NRA) des différents comportements au cours du processus électrochrome a mis en évidence que le mécanisme ne peut être simplement décrit par une unique réaction d’insertion/désinsertion. Les propriétés électrochromes prometteuses des couches unitaires de V2O5 (métal V2O5RF) ont permis leur intégration dans des dispositifs complets à base d’électrolyte transparent ou opaque. Ainsi, des dispositifs WO3/V2O5 et V2O5/V2O5 ont été caractérisés pour des applications vitrage et afficheur.
Vanadium oxide thin films were deposited on ITO coated glass substrate at room temperature using three different deposition conditions, namely radio frequency magnetron sputtering (RFMS) with V metallic target (V2O5RF-metal) or V2O5 oxide target (V2O5RF-oxide) and High Power Impulse Magnetron Sputtering (HiPIMS) with V metallic target (V2O5HiPIMS), respectively. Significant difference in structure and morphologies are reported. V2O5RF-metal films are crystalline and dense with a disturbed surface which is thickness dependent, while V2O5RF-oxide and V2O5HiPIMS films are amorphous and porous or dense respectively. V2O5 thin films show reversible electrochromism with 4 colors, which are orange, green, blue and gray, in reduction/oxidation states when cycled in Li and Na based electrolytes. However, depending on the deposition method, V2O5 films show different cycling stability, recorded up to 1000 cycles, that is attributed to a modification of the morphology (i.e. increase of the surface area due to cracks and increase porosity, as well as a progressive amorphization particularly in lithium electrolyte. The different behaviors during the electrochromic process were investigated with GIXRD, XPS, TOF-SIMS, AES and RBS/NRA indicating a mechanism more complex than a simple insertion/deinsertion. Finally, two types of ECDs using either transparent electrolyte membrane or opaque are fabricated coupling V2O5 thin films to WO3 or to V2O5 in a symmetrical device aiming at application in smart windows and displays, respectively.
Abstract
To date, numerous researchers have spent great efforts in searching for transition metal oxides with diverse properties. Vanadium oxide are a family of interesting materials with high ...catalytic, electrical, optical and magnetic properties and potential applications such as thermochromic smart windows, batteries and electrochromic devices1-2. In this study, vanadium oxide thin films were deposited by two techniques, namely, reactive RF magnetron sputtering and Doctor Blade leading to V
2
O
5
films with a wide range of optical properties. RF sputtered films deposited in gas mixture of argon and oxygen at room temperature on ITO substrates crystallized in an orthorhombic structure when using a V metal target while they were amorphous from V
2
O
5
target. Depending on the deposition conditions, the film morphology was layer or needle type. Orthorhombic V
2
O
5
thin fims were prepared by Doctor Blade deposition on ITO substrate from V
2
O
5
powder synthesized by polyol process3-4. Independently of the deposition technique, the electrochromic properties of vanadium oxide films showed multi steps electrochromism, namely yellow to green, green to blue, and blue to grey, in lithium based electrolyte. The optical transmittance characterized by UV-visible spectrophotometer showed a maximum difference of 40% at 550 nm for RF sputtered films while a contrast in reflectance of 20%, in the spectral region 550-700nm, was recorded for Doctor Blade films. The influence of lithium insertion/desinsertion in the structure and chemical state was investigated using GIXD and XPS analysis. The relationship between the film structure, morphology, thickness, correlated with their deposition conditions and the EC mechanism will be discussed. References
Cao Z and Wei B, V
2
O
5
/single-walled carbon nanotube hybrid mesoporous films as cathodes with high-rate capacities for recharge able lithium ion batteries,
Nano Energy
2, 481 (2013).
Yaoming Sun
et al
., Anisotropic vanadium dioxide sculptured thin films with superior thermochromic properties,
Scientific Reports
, 3, 2756 (2013).
I. Mjejri, L. Manceriu, M. Gaudon, A. Rougier, F. Sediri, Solid State Ionics, 292 8-14 (2016).
I. Mjejri, A; Rougier, M. Gaudon, Inorganic Chemistry, Submitted.
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