| 1. |
- Sorar, Idris, et al.
(författare)
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Electrochromism in Ni Oxide Thin Films Made by Advanced Gas Deposition and Sputtering : A Comparative Study Demonstrating the Significance of Surface Effects
- 2020
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 167:11
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Tidskriftsartikel (refereegranskat)abstract
- Films of electrochromic Ni oxide, with thickness in the ∼100–1000-nm range, were prepared by reactive advanced gas deposition (AGD) and, for comparison, also by reactive DC magnetron sputtering (MS). Voltammetric cycling was performed in an electrolyte of lithium perchlorate in propylene carbonate in the voltage range 2.0–4.1 V vs Li/Li+, and concurrent optical transmittance modulation was studied at a wavelength of 530 nm. For the thickest films, the optical modulation range was as large as ∼54% and the maximum transmittance was ∼82% for deposition by AGD, whereas the corresponding numbers were ∼45% and ∼87% for MS. Rutherford backscattering spectrometry together with measurements of film thickness demonstrated that the porosity of 400–500-nm-thick films made by AGD and MS were ∼84% and ∼45%, respectively. The charge exchange per mass unit was as high as 48–67 C g–1 for samples made by AGD. The corresponding number was much lower for MS, namely 13–18 C g–1. These results lend convincing support to the view that the electrochromism of Ni-oxide-based films in Li-ion-conducting electrolytes is dominated by surface effects.
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| 2. |
- Atak, Gamze, et al.
(författare)
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Cycling durability and potentiostatic rejuvenation of electrochromic tungsten oxide thin films : Effect of silica nanoparticles in LiClO4-Propylene carbonate electrolytes
- 2023
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier. - 0927-0248 .- 1879-3398. ; 250
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Tidskriftsartikel (refereegranskat)abstract
- Electrochromic (EC) technology allows control of the transmission of visible light and solar radiation through thin-film devices. When applied to “smart” windows, EC technology can significantly diminish energy use for cooling and air conditioning of buildings and simultaneously provide good indoor comfort for the buildings’ occupants through reduced glare. EC “smart” windows are available on the market, but it is nevertheless important that their degradation under operating conditions be better understood and, ideally, prevented. In the present work, we investigated EC properties, voltammetric cycling durability, and potentiostatic rejuvenation of sputter-deposited WO3 thin films immersed in LiClO4–propylene carbonate electrolytes containing up to 3.0 wt% of ∼7-nm-diameter SiO2 nanoparticles. Adding about 1 wt% SiO2 led to a significant improvement in cycling durability in the commonly used potential range of 2.0–4.0 V vs. Li/Li+. Furthermore, X-ray photoemission spectroscopy indicated that O–Si bonds were associated with enhanced durability in the presence of SiO2 nanoparticles.
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| 3. |
- Atak, Gamze, et al.
(författare)
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Electrochromism of nitrogen-doped tungsten oxide thin films
- 2020
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Ingår i: Materials Today. - : Elsevier BV. - 2214-7853. ; 33:6, s. 2434-2439
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Tidskriftsartikel (refereegranskat)abstract
- Tungsten-oxide-based thin films were prepared by reactive DC magnetron sputtering in the presence ofoxygen and nitrogen. Nitrogen contents up to 12 at.% were documented by Rutherford backscattering spectrometry and time-of-flight elastic recoil detection analysis. Optical and electrochemical measurements showed that films with up to 4 at.% of nitrogen were as transparent as undoped tungsten oxide films and displayed enhanced electrochromic properties manifested in an increase in the coloration efficiency by as much as 20%.
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| 4. |
- Pehlivan, Esat, et al.
(författare)
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Electrochromic nickel-oxide-based thin films in KOH electrolyte : Ionic and electronic effects elucidated by impedance spectroscopy
- 2024
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier. - 0927-0248 .- 1879-3398. ; 269
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Tidskriftsartikel (refereegranskat)abstract
- Ni-oxide-based thin films, prepared by sputtering, are investigated by electrochemical impedance spectroscopy in a KOH electrolyte. The films are electrochromic, and an increase of the applied potential leads to a variation from a bleached to a colored state as a result of proton (H+) extraction together with extraction of electrons from the valence band. The complex frequency-dependent impedance displays different features in different potential ranges. At low potentials, where coloration is weak, the spectra give evidence for a constant-phase element in parallel with a leak resistance. At intermediate and high potentials, the impedance spectra indicate the presence of a diffusion process, and a model for anomalous diffusion gives excellent fits to the spectra except in a crossover region. The applicability of this model in a significant part of the studied potential range suggests the presence of a multiple-trapping process for the ions. The potential dependence of the chemical capacitance, as well as the diffusion coefficient of un-trapped ions, are analyzed. The electrochemical density-of-states of the chargecompensating electrons gives indications of the top of the valence band and of a band tail extending into the band gap. Diffusion coefficients are found to increase steeply in the crossover potential region to very high values at high potentials. These features are discussed and related to the electrochromic behavior of Ni-oxide-based thin films.
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| 5. |
- Pehlivan, Esat, et al.
(författare)
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Impedance Spectroscopy of Electrochromic Hydrous Tungsten Oxide Films
- 2021
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Ingår i: Electronic Materials. - : MDPI. - 2673-3978. ; 2:3, s. 312-323
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Tidskriftsartikel (refereegranskat)abstract
- Tungsten oxide is a widely used electrochromic material with important applications in variable-transmittance smart windows as well as in other optoelectronic devices. Here we report on electrochemical impedance spectroscopy applied to hydrous electrochromic tungsten oxide films in a wide range of applied potentials. The films were able to reversibly bleach and color upon electrochemical cycling. Interestingly, the bleaching potential was found to be significantly higher than in conventional non-hydrous tungsten oxide films. Impedance spectra at low potentials showed good agreement with anomalous diffusion models for ion transport in the films. At high potentials,where little ion intercalation takes place, it seems that parasitic side reactions influence the spectra. The potential dependence of the chemical capacitance, as well as the ion diffusion coefficient, were analyzed. The chemical capacitance is discussed in terms of the electron density of states in the films and evidence was found for a band tail extending below the conduction band edge.
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| 6. |
- Sorar, Idris, et al.
(författare)
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Cycling Durability of Electrochromic W-Ti Oxide Thin Films : Optical Transmittance Data Signal Dual Degradation Modes
- 2020
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 167:2
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical degradation of electrochromic W oxide and W–Ti oxide thin films, prepared by reactive DC magnetron sputtering, was studied by voltammetric cycling in potential intervals from 1.5–4.0 to 2.0–4.0 V vs Li/Li+ in an electrolyte of lithium perchlorate in propylene carbonate. Cycling-dependent evolution of the upper and lower limits for the optical modulation range was critically dependent on potential interval. This phenomenon was analyzed through an extension of a previously formulated model for power-law dynamics; it was discovered that the upper and lower limits for the optical modulation range varied in distinctly different ways, and that only data acquired in the interval 2.0–4.0 V vs Li/Li+ could be reconciled with dispersive chemical kinetics. We thus find that our data on optical transmittance degradation lends strong support to the existence of dual degradation modes for electrochromism upon extended electrochemical cycling. This result is of great importance for the development of highly durable electrochromic devices such as smart windows for energy-efficient buildings. The present article is a sequel to a recent publication of ours [J. Electrochem. Soc., 166, H795 (2019)].
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| 7. |
- Sorar, Idris, et al.
(författare)
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Durability and rejuvenation of electrochromic tungsten oxide thin films in LiClO4-propylene carbonate viscous electrolyte : Effect of Ti doping of the film and polyethylene oxide addition to the electrolyte
- 2023
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Ingår i: Solid State Sciences. - : Elsevier. - 1293-2558 .- 1873-3085. ; 137
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Tidskriftsartikel (refereegranskat)abstract
- Tungsten oxide and titanium doped tungsten oxide thin films, deposited by sputtering, were immersed in a viscous electrolyte comprised of LiClO4 in propylene carbonate and 2.0 wt% of polyethylene oxide (PEO). Electrochromic properties of the films were investigated by electrochemical techniques and in situ transmittance measurements. Cyclic voltammetry data were taken in the voltage ranges 2.0–4.0 and 1.5–4.0 V vs Li/Li+ for up to 500 cycles. A potentiostatic rejuvenation treatment was then performed on the degraded electrochromic films, at 6.0 V for 20 h, which was subsequently followed by another cyclic voltammetry measurement. Titanium incorporation into tungsten oxide resulted in a small cyclic stability improvement in the 2.0–4.0-V range, whereas less pronounced effects were observed for cycling in the 1.5–4.0-V range. Combining the results of the present study with our previous work, we are able to assess the relative merits of titanium incorporation and PEO addition to the electrolyte for the durability of electrochromic tungsten oxide thin films. Titanium addition was found advantageous for electrochemical durability in the 2.0–4.0-V range, but no clear benefits of PEO in the electrolyte were seen. On the other hand, in the wider 1.5–4.0-V range, tungsten oxide exhibited better durability than titanium-containing films, and this was especially so after rejuvenation in the PEO-containing electrolyte.
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| 8. |
- Sorar, Idris, et al.
(författare)
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Electrochromism of W-In oxide thin films : Implications for cycling durability
- 2020
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 697
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Tidskriftsartikel (refereegranskat)abstract
- Electrochromic W oxide and W–In oxide thin films were prepared by dual-target reactive DC magnetron sputtering and were cycled voltammetrically in an electrolyte of lithium perchlorate in propylene carbonate. Film degradation was investigated for up to 500 cycles in the voltage ranges 1.5–4.0, 1.7–4.0 and 2.0–4.0 V vs. Li/Li+, and optical transmittance was recorded concurrently. Indium doping was found to be unambiguously detrimental to electrochromic cycling durability, which resolves an outstanding issue related to recently discovered unprecedented durability of potentiostatically pretreated W oxide films backed by In2O3:Sn and gives strong support in favor of beneficial effects of solid-electrolyte interfacial layers.
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| 9. |
- Sorar, Idris, et al.
(författare)
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Potentiostatic rejuvenation of electrochromic WO3 thin films : Exploring the effect of polyethylene oxide in LiClO4-Propylene carbonate electrolytes
- 2020
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier. - 0927-0248 .- 1879-3398. ; 218
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of electrochromic (EC) W oxide were prepared by reactive DC magnetron sputtering and were immersed in electrolytes of LiClO4 in propylene carbonate with 0.5–3.0 wt% of added polyethylene oxide (PEO). Charge density and optical modulation range were found to diminish monotonically upon prolonged voltammetric cycling with concurrent optical transmittance measurements for up to 500 and 200 cycles in the voltage ranges 2.0–4.0 and 1.5–4.0 V vs. Li/Li+, respectively. Rejuvenation of the degraded EC films was then accomplished by potentiostatic treatment at 6.0 V vs. Li/Li+ for 20 h and has been ascribed to expulsion of trapped Li ions. Importantly, degradation subsequent to rejuvenation was found to progress at a significantly lowered pace than for as-deposited films—in proportion with the amount of PEO—especially for harsh voltammetric cycling in the voltage range 1.5–4.0 V vs. Li/Li+. The results of this explorative study are of considerable value for the development of highly durable EC devices such as polymer-laminated smart glazing for energy efficient buildings with excellent indoor comfort.
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