| 1. |
- Arvizu, Miguel A, et al.
(author)
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Electrochemical pretreatment of electrochromic WO3 films gives greatly improved cycling durability
- 2018
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In: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 653, s. 1-3
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Journal article (peer-reviewed)abstract
- Electrochromic WO3 thin films have important applications in devices such as smart windows for energy-efficient buildings. Long-term electrochemical cycling durability of these films is essential and challenging. Here we investigate reactively sputter-deposited WO3 films, backed by indium-tin oxide layers and immersed in electrolytes of LiClO4 in propylene carbonate, and demonstrate unprecedented electrochemical cycling durability after straight-forward electrochemical pretreatments by the application of a voltage of 6 V vs. Li/Li+ for several hours.
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| 2. |
- Arvizu, Miguel A, et al.
(author)
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Electrochromic WO3 thin films attain unprecedented durability by potentiostatic pretreatment
- 2019
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In: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 7:6, s. 2908-2918
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Journal article (peer-reviewed)abstract
- Electrochromic windows and glass facades are able to impart energy efficiency jointly with indoor comfort and convenience. Long-term durability is essential for practical implementation of this technology and has recently attracted broad interest. Here we show that a simple potentiostatic pretreatment of sputterdeposited thin films of amorphous WO3-the most widely studied electrochromic material-can yield unprecedented durability for charge exchange and optical modulation under harsh electrochemical cycling in a Li-ion-conducting electrolyte and effectively evades harmful trapping of Li. The pretreatment consisted of applying a voltage of 6.0 V vs. Li/Li+ for several hours to a film backed by a transparent conducting In2O3: Sn layer. Associated compositional and structural modifications were probed by several techniques, and improved durability was associated with elemental intermixing at the WO3/ITO and ITO/glass boundaries as well as with carbonaceous solid-electrolyte interfacial layers on the WO3 films. Our work provides important new insights into long-term durability of ion-exchange-based devices.
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| 3. |
- Granqvist, Claes Göran, 1946-, et al.
(author)
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Electrochromic materials and devices for energy efficiency and human comfort in buildings : A critical review
- 2018
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In: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 259, s. 1170-1182
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Research review (peer-reviewed)abstract
- Electrochromic (EC) materials can be integrated in thin-film devices and used for modulating optical transmittance. The technology has recently been implemented in large-area glazing (windows and glass facades) in order to create buildings which combine energy efficiency with good indoor comfort. This critical review describes the basics of EC technology, provides a case study related to EC foils for glass lamination, and discusses a number of future aspects. Ample literature references are given with the object of providing an easy entrance to the burgeoning research field of electrochromics.
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| 4. |
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| 5. |
- Niklasson, Gunnar A., Professor, 1953-, et al.
(author)
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Durability of electrochromic films : Aging kinetics and rejuvenation
- 2017
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In: ECS Transactions. - : Electrochemical Society. ; , s. 1659-1669
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Conference paper (peer-reviewed)abstract
- A major challenge for energy-efficient smart window technology is to ensure the durability of electrochromic (EC) devices over aservice life of more than 20 years. In this paper, we report recent results from a fundamental study of the aging kinetics of EC tungsten oxide and nickel oxide thin films and describe electrochemical rejuvenation mechanisms that are able to restore the films to their initial state. The aging kinetics displays an approximate power-law decrease of the charge capacity as a function of cycle number. This decay of charge capacity can be understood in terms of models built on so-called dispersive chemical kinetics. Tungsten oxide and nickel oxide EC films can be rejuvenated by applying a high electrochemical potential or a small constant current. Trapped ions in the bulk or at the surface of the films can be released by these procedures.
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| 6. |
- Niklasson, Gunnar, 1953-, et al.
(author)
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Electrochemical rejuvenation of Tungsten oxide electrochromic thin films : Evidence from impedance spectroscopy
- 2018
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In: 13th International Meeting on Electrochromism, IME-13. ; , s. 11-
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Conference paper (peer-reviewed)abstract
- A major challenge for energy-efficient smart window technology is to ensure the durability of electrochromic (EC) devices capable of render a service life significantly higher than 20 years. The development of more durable EC materials would also make it possible to increase the transmittance contrast between bleached and colored states without the risk of limiting service life. Recently, it has been shown that degraded EC coatings can be restored to their initial state by electrochemical rejuvenation treatments.1,2 In addition, it was found that tungsten oxide EC films could gain vastly improved durability after extended electrochemical treatments at high applied potentials.3 In this paper we present an attempt to unravel the complex mechanisms behind high potential rejuvenation and durability-enhancing treatments. We study EC amorphous tungsten oxide, which is the most commonly used EC oxide. It is used in most commercial device designs, often in combination with a nickel oxide-based complementary EC layer.Amorphous tungsten oxide thin films were deposited by sputtering onto conducting indium-tin oxide (ITO) coated glass substrates. Ion intercalation and diffusion in the films were studied by electrochemical impedance spectroscopy measurements in the frequency range 10 mHz-10 kHz and for potentials between 2.0 and 3.3 V vs. Li/Li+, using the film as working electrode in a Li+ containing electrolyte. Measurements were carried out for as-deposited EC tungsten oxide films, degraded and rejuvenated films as well as durability-enhanced WOx films. The impedance data were in good agreement with a Randles-type equivalent circuit containing an anomalous diffusion element.4 In this study we focus on changes at the electrolyte/EC film and EC film/ITO interfaces during degradation and after different electrochemical treatments.The most notable changes were associated with the high frequency and charge transfer resistances. The high frequency resistance increased significantly during degradation as well as extended rejuvenation treatments; a similar effect was observed in durability-enhanced WOx films. This might indicate compositional or chemical changes in the ITO backing or at the film/ITO interface. The charge transfer resistance associated with the electrolyte/film interface also increased after treatments, but in addition exhibited a strong potential dependence. The appearance of a second high-frequency process after rejuvenation is considered to be more interesting. Possible explanations include an additional adsorption step preceding ion intercalation into the EC film, or alternatively the appearance of a solid-electrolyte interphase layer of the type commonly observed in Li-ion batteries.Ion diffusion coefficients were not significantly different for rejuvenated EC films as compared to the as-deposited ones. On the other hand degraded films exhibited a completely different impedance response, which could be interpreted as being due to parasitic chemical reactions in the system.An increased understanding of ageing and rejuvenation processes will facilitate the search for more durable EC materials and preliminary results suggest that interfacial characteristics may influence durability. Eventually, improved EC coatings will be important for large-scale practical application of electrochromic materials, for example in smart windows. References[1] R.-T. Wen, C.G. Granqvist, G.A. Niklasson, Nature Mater., 14, 996 (2015).[2] H.-Y. Qu, D. Primetzhofer, M.A. Arvizu, Z. Qiu, U. Cindemir, C.G. Granqvist, G.A. Niklasson, ACS Appl. Mater. Interf., 9, 42420 (2017).[3] M.A. Arvizu, H.-Y. Qu, G.A. Niklasson, C.G. Granqvist, Thin Solid Films, 653, 1 (2018).[4] S. Malmgren, S.V. Green, G.A. Niklasson, Electrochim. Acta, 247, 252 (2017).
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| 7. |
- Qu, Hui-Ying, et al.
(author)
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Cation/Anion-based electrochemical degradation and rejuvenation of electrochromic nickel oxide films
- 2018
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In: ChemElectroChem. - : Wiley. - 2196-0216. ; 5:22, s. 3548-3556
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Journal article (peer-reviewed)abstract
- Ni oxide thin films are widely used in electrochromic (EC) devices with variable throughput of visible light and solarenergy. However, the mechanisms underlying the optical modulation – and its degradation under extended operationand subsequent rejuvenation – are poorly understood especially for Li+-conducting electrolytes. Here, we report a comprehensive study of the EC properties of sputter-deposited Ni oxide films immersed in an electrolyte of LiClO4 in propylene carbonate. Cyclic voltammetry and optical transmittance measurements were used to document degradation and subsequent potentiostatic rejuvenation. X-ray diffraction did not show evidence for accompanying changes in crystallinity, whereas vibrational spectroscopy indicated that degraded films had carbonaceous surface layers. Time-of-flight elastic recoil detection analysis demonstrated that both Li+ and Cl-based ions participate in the electrochromism and its degradation and rejuvenation. A major result was that degradation is associated with a reduced difference in the concentrations of Li+ and Cl based ions in the nickel oxide during extended electrochemical cycling, and rejuvenation of degraded films is achieved by removal of Li+ ions and accumulation of Cl-based anions to regain their initial concentration difference. Our work provides new insights into the use of ion-exchange-based devices incorporating nickel oxide.
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| 8. |
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| 9. |
- Qu, Hui-Ying, et al.
(author)
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Electrochemical Rejuvenation of Anodically Coloring Electrochromic Nickel Oxide Thin Films
- 2017
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; :9, s. 42420-42424
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Journal article (peer-reviewed)abstract
- Nickel oxide thin films are of major importance as anodically coloring components in electrochromic smart windows with applications in energy-efficient buildings. However, the optical performance of these films degrades upon extended electrochemical cycling, which has hampered their implementation. Here, we use a potentiostatic treatment to rejuvenate degraded nickel oxide thin films immersed in electrolytes of LiClO4 in propylene carbonate. Time-of-flight elastic recoil detection analysis provided unambiguous evidence that both Li+ ions and chlorine-based ions participate in the rejuvenation process. Our work provides new perspectives for developing ion-exchange-based devices embodying nickel oxide.
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| 10. |
- Qu, Hui-Ying, et al.
(author)
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Enhanced durability of Tungsten oxide electrochromic films : Processes occurring at the Indium-Tin oxide substrate
- 2018
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In: IS-TCMs. ; , s. 215-215
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Conference paper (peer-reviewed)abstract
- Durability is a key issue for ensuring widespread and successful use of electrochromic(EC) films in energy-efficient smart windows and also for other devices such as lithium-ionbatteries and supercapacitors. Recent results showed [1] that the durability of EC WO3 thinfilms can be greatly improved by a facile electrochemical treatment at high potentials. Glass coated with In2O3:Sn (ITO) was then used as the substrate, and here we present evidence that changes in the properties of the ITO substrate is connected with the improved durability.We deposited a ~300-nm-thick WO3 film on ITO-coated glass with a sheet resistance of 60 Ω/sq and then applied 6 V vs. Li/Li+ to pretreat the WO3 thin film for 24 h in an electrolyte of LiClO4 in propylene carbonate. After the pretreatment, the durability of the WO3 thin film was excellent even after harsh electrochemical cycling in the 1.5–4 V vs. Li/Li+ range. Scanning electron microscopy showed that the thickness of the ITO layer became smaller after the pretreatment. X-ray photoelectron spectroscopy (XPS) depth profile measurements (Fig. 1) demonstrated that the concentration of In and Sn decreased significantly after pretreatment. In addition, the depth profile indicates a significant intermixing of W and In, which even seems to extend into the underlying glass. Supplementary impedance spectroscopy measurements showed that the high-frequency resistance (mainly due to the ITO) increased significantly after the pretreatment.We also studied the behavior of ITO films with a sheet resistance of 60 Ω/sq by cyclic voltammetry. XPS measurements verified a strong decrease of In and Sn contents as well asITO thickness when the upper potential exceeded 6 V vs. Li/Li+. We propose that these interactions between WO3 and the ITO substrate, as well as physical changes in the ITO, have a positive effect on the durability of the EC WO3 thin film. This discovery may be of interest for ITO-based electronic devices as well as for designing long-time-durable EC devices.
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