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Rojas González, Edgar AlonsoORCID iD iconorcid.org/0000-0003-0393-0273
Publications (8 of 8) Show all publications
Arvizu, M. A., Qu, H.-Y., Cindemir, U., Qiu, Z., Rojas González, E. A., Primetzhofer, D., . . . Niklasson, G. (2019). Electrochromic WO3 thin films attain unprecedented durability by potentiostatic pretreatment. Journal of Materials Chemistry A, 7(6), 2908-2918
Open this publication in new window or tab >>Electrochromic WO3 thin films attain unprecedented durability by potentiostatic pretreatment
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2019 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, no 6, p. 2908-2918Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2019
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-378529 (URN)10.1039/c8ta09621j (DOI)000457893400054 ()
Funder
EU, European Research Council, 267234Swedish Research Council, 821-2012-5144Swedish Research Council, 2017-00646_9Swedish Foundation for Strategic Research , RIF14-0053
Available from: 2019-03-22 Created: 2019-03-22 Last updated: 2019-03-22Bibliographically approved
Sorar, I., Rojas González, E. A., Bayrak Pehlivan, I., Granqvist, C. G. & Niklasson, G. (2019). Electrochromism of W–Ti Oxide Thin Films: Cycling Durability,Potentiostatic Rejuvenation, and Modelling of Electrochemical Degradation. Journal of the Electrochemical Society, 166(15), H795-H801
Open this publication in new window or tab >>Electrochromism of W–Ti Oxide Thin Films: Cycling Durability,Potentiostatic Rejuvenation, and Modelling of Electrochemical Degradation
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2019 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 166, no 15, p. H795-H801Article in journal (Refereed) Published
Abstract [en]

Thin films of electrochromicWoxide and W–Ti oxide were prepared by reactive DC magnetron sputtering and were cycled voltammetrically in an electrolyte of lithium perchlorate in propylene carbonate. Film degradation was studied for up to 500 voltammetric cycles in voltage ranges between 1.5–4.0 and 2.0–4.0 V vs. Li/Li+. Optically and electrochemically degraded films were subjected to potentiostatic posttreatment at 6.0 V vs. Li/Li+ to achieve ion de-trapping and rejuvenation so that the films partly regained their original properties. Ti incorporation and potentiostatic posttreatment jointly yielded superior electrochromic properties provided the lower limit of the voltage range was above 1.6–1.7 V vs. Li/Li+. Degradation dynamics for as-deposited and rejuvenated thin films was modeled successfully by power-law kinetics; this analysis indicated coexistence of two degradation mechanisms, one based on dispersive chemical kinetics and operating universally and another, of unknown origin, rendered inactive by rejuvenation. The results of the present study are of large interest for the development of electrochromic devices with exceptional durability.

Place, publisher, year, edition, pages
Electrochemical Society, 2019
National Category
Condensed Matter Physics
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-397482 (URN)DOI: 10.1149/2.0421915jes (DOI)000494283100001 ()
Funder
Swedish Research Council, VR-2016-03713Swedish Research Council, 2017-00646-9Swedish Foundation for Strategic Research , RIF14-0053
Available from: 2019-11-20 Created: 2019-11-20 Last updated: 2019-11-22Bibliographically approved
Qu, H.-Y., Rojas-González, E. A., Granqvist, C. G. & Niklasson, G. A. (2019). Potentiostatically pretreated electrochromic tungsten oxide films with enhanced durability: Electrochemical processes at interfaces of indium–tin oxide. Thin Solid Films, 682, 163-168
Open this publication in new window or tab >>Potentiostatically pretreated electrochromic tungsten oxide films with enhanced durability: Electrochemical processes at interfaces of indium–tin oxide
2019 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 682, p. 163-168Article in journal (Refereed) Published
Abstract [en]

Recent work has shown that electrochromic WO3 films, backed by In2O3:Sn (ITO) and immersed in a lithium-ion-conducting electrolyte, can attain unprecedented electrochemical cycling durability after potentiostatic pretreatment at high voltage. Here we demonstrate that this intriguing feature is associated with changes in the properties of the ITO film. Specifically, we studied thin films of ITO and WO3/ITO immersed in an electrolyte of LiClO4 in propylene carbonate at potentials up to 6.0 V vs. Li/Li+ by cyclic voltammetry and impedance spectroscopy and present evidence that electrochemical reactions occur under these conditions. X-ray photoemission spectroscopy indicated that the ITO film was partly dissolved at high voltages and that the dissolution reaction promoted diffusion of In and Sn into the WO3 film.

Keywords
Indium-tin oxide, Electrochemistry, Dissolution reaction, Tungsten oxide, Electrochromism
National Category
Other Materials Engineering
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-385819 (URN)10.1016/j.tsf.2019.02.027 (DOI)000468626200023 ()
Funder
Swedish Research Council, VR-2016-03713
Note

De 2 första författarna delar förstaförfattarskapet.

Available from: 2019-06-17 Created: 2019-06-17 Last updated: 2019-12-06Bibliographically approved
Rojas González, E. A. & Niklasson, G. (2019). Setup for simultaneous electrochemical and color impedance measurements of electrochromic films: Theory, assessment, and test measurement. Review of Scientific Instruments, 90(8), Article ID 085103.
Open this publication in new window or tab >>Setup for simultaneous electrochemical and color impedance measurements of electrochromic films: Theory, assessment, and test measurement
2019 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 90, no 8, article id 085103Article in journal (Refereed) Published
Abstract [en]

Combined frequency-resolved techniques are suitable to study electrochromic (EC) materials. We present an experimental setup for simultaneous electrochemical and color impedance studies of EC systems in transmission mode and estimate its frequency-dependent uncertainty by measuring the background noise. We define the frequency-dependent variables that are relevant to the combined measurement scheme, and a special emphasis is given to the complex optical capacitance and the complex differential coloration efficiency, which provide the relation between the electrical and optical responses. Results of a test measurement on amorphous WO3 with LED light sources of peak wavelengths of 470, 530, and 810 nm are shown and discussed. In this case, the amplitude of the complex differential coloration efficiency presented a monotonous increase down to about 0.3 Hz and was close to a constant value for lower frequencies. We study the effect of the excitation voltage amplitude on the linearity of the electrical and optical responses for the case of amorphous WO3 at 2.6 V vs Li/Li+, where a trade-off should be made between the signal-to-noise ratio (SNR) of the optical signal and the linearity of the system. For the studied case, it was possible to increase the upper accessible frequency of the combined techniques (defined in this work as the upper threshold of the frequency region for which the SNR of the optical signal is greater than 5) from 11.2 Hz to 125.9 Hz while remaining in the linear regime with a tolerance of less than 5%. (C) 2019 Author(s).

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2019
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-394164 (URN)10.1063/1.5115119 (DOI)000483885600066 ()31472623 (PubMedID)
Funder
Swedish Research Council, VR-2016-03713
Available from: 2019-10-09 Created: 2019-10-09 Last updated: 2019-10-09Bibliographically approved
Rojas González, E. A., Borne, A., Boulanger, B., Levenson, J. & Bencheikh, K. (2018). Continuous-Variable Triple-Photon States Quantum Entanglement. Physical Review Letters, 120(4), Article ID 043601.
Open this publication in new window or tab >>Continuous-Variable Triple-Photon States Quantum Entanglement
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2018 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 120, no 4, article id 043601Article in journal (Refereed) Published
Abstract [en]

We investigate the quantum entanglement of the three modes associated with the three-photon states obtained by triple-photon generation in a phase-matched third-order nonlinear optical interaction. Although the second-order processes have been extensively dealt with, there is no direct analogy between the second and third-order mechanisms. We show, for example, the absence of quantum entanglement between the quadratures of the three modes in the case of spontaneous parametric triple-photon generation. However, we show robust, seeding-dependent, genuine triple-photon entanglement in the fully seeded case.

National Category
Other Materials Engineering
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-340481 (URN)10.1103/PhysRevLett.120.043601 (DOI)000423319200002 ()29437405 (PubMedID)
Available from: 2018-01-31 Created: 2018-01-31 Last updated: 2018-03-07Bibliographically approved
Rojas González, E. A., Qu, H.-Y., Granqvist, C. G. & Niklasson, G. (2018). Electrochemical impedance spectroscopy analysis of Indium-Tin oxide films at high applied potentials. In: IS-TCMs: 7^th International Symposium on Transparent Conductive Materials and 4^th E-MRS & MRS-J Bilateral Symposium on Advanced Oxides and Wide Bandgap Semiconductors, Chania Crete Grekland. Paper presented at 7^th International Symposium on Transparent Conductive Materials and 4^th E-MRS & MRS-J Bilateral Symposium on Advanced Oxides and Wide Bandgap Semiconductors, Chania Crete Greece, Oct 14-19, 2018 (pp. 223). , Article ID PS1-33.
Open this publication in new window or tab >>Electrochemical impedance spectroscopy analysis of Indium-Tin oxide films at high applied potentials
2018 (English)In: IS-TCMs: 7^th International Symposium on Transparent Conductive Materials and 4^th E-MRS & MRS-J Bilateral Symposium on Advanced Oxides and Wide Bandgap Semiconductors, Chania Crete Grekland, 2018, p. 223-, article id PS1-33Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

Indium-tin oxide (ITO) coated substrates are readily used as transparent conductors in energy-related applications like photovoltaics and smart window technology. Recently, it has been reported that electrochemical treatments at high applied voltages can enhance the durability of electrochromic (EC) films [1], and in addition rejuvenate already degraded films [2]. However, the EC electrode consists of an EC film on a transparent conductor, usually ITO, and changes in the ITO film may affect the durability and rejuvenation properties of the system. In a Li+-containing electrolyte, the safe potential range of ITO is 2-4 V vs. Li/Li+. At low potentials below 2 V vs. Li/Li+ Li compounds will form and result in a color change of ITO [3]. However, the behavior of ITO in Li+-containing electrolyte at high potentials up to 6 V vs. Li/Li+ is to our knowledge virtually unknown.   

In this work, ITO coated glass substrates with nominal sheet resistance of 60 Ω/sq, and 15 Ω/sq, having thicknesses of 50 nm, and 150 nm, respectively were used as working electrodes (WE) in a three-electrode electrochemical cell. Lithium foils were used both as counter and reference electrodes in an electrolyte consisting of 1 M LiClO4 dissolved in propylene carbonate.

A potentiostatic pretreatment at 6 V vs Li/Li+ during 24 h was applied on the WE. The current during the pretreatment showed an initial rapid decrease followed by a plateau, after which it decreased ~2 orders of magnitude. The width of the plateau for the 15 Ω/sq film was ~3 times longer than for the 60  Ω/sq film, which correlates to their thickness ratio. Cyclic voltammetry between 3.5 V and 6 V vs. Li/Li+ showed a significant current response only for potentials above 5 V for an as-deposited sample, and very little activity for a pretreated WE. The latter result indicates that the film had been stabilized by the pre-treatment.

Electrochemical impedance spectroscopy (EIS) spectra were measured at pseudo equilibrium potentials from 3.5 V vs. Li/Li+, and up to 6 V vs. Li/Li+. The spectra were modeled and fitted in terms of equivalent circuits. The spectra for potentials below 5 V were dominated by a blocking electrode response, whereas for higher voltages a low-frequency response was identified as being due to an electrochemical reaction which becomes more intense as the potential is increased. In addition the high frequency series resistance, mainly due to the ITO, is increased at high voltages and after pretreatment. Supplementary investigations by Scanning electron microscopy and X-ray photoelectron spectroscopy gave evidence for a smaller film thickness and a significantly decreased In content in films exposed to treatments at high potentials.

A better understanding of the effects of high applied potentials on transparent conductors like ITO will help to unravel mechanisms of durability enhancement and rejuvenation, and may provide guidelines for designing new procedures to enhance the durability of EC systems for energy-efficient smart windows.

 

1. M.A. Arvizu, H.-Y Qu, G.A. Niklasson and C.G. Granqvist, Thin Solid Films 653 (2018) 1-3.

2. R.-T. Wen, G.A. Niklasson and C.G. Granqvist, Nature Materials, 14 (2015) 996-1001.

3. P.M.M.C. Bressers and E.A. Meulenkamp, J. Electrochem. Soc. 145 (1998) 2225-2230.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-369143 (URN)
Conference
7^th International Symposium on Transparent Conductive Materials and 4^th E-MRS & MRS-J Bilateral Symposium on Advanced Oxides and Wide Bandgap Semiconductors, Chania Crete Greece, Oct 14-19, 2018
Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2018-12-17
Niklasson, G., Abatte, L., Rojas González, E. A., Arvizu, M. A., Qu, H.-Y. & Granqvist, C. G. (2018). Electrochemical rejuvenation of Tungsten oxide electrochromic thin films: Evidence from impedance spectroscopy. In: 13th International Meeting on Electrochromism, IME-13: Book of Abstracts. Paper presented at 13th International Meeting on Electrochromism, Chiba University, Chiba, Japan, Aug 27-31, 2018 (pp. 11). , Article ID IN-3.
Open this publication in new window or tab >>Electrochemical rejuvenation of Tungsten oxide electrochromic thin films: Evidence from impedance spectroscopy
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2018 (English)In: 13th International Meeting on Electrochromism, IME-13: Book of Abstracts, 2018, p. 11-, article id IN-3Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

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).

 

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-368961 (URN)
Conference
13th International Meeting on Electrochromism, Chiba University, Chiba, Japan, Aug 27-31, 2018
Available from: 2018-12-10 Created: 2018-12-10 Last updated: 2019-03-07Bibliographically approved
Qu, H.-Y., Rojas González, E. A., Granqvist, C. G. & Niklasson, G. (2018). Enhanced durability of Tungsten oxide electrochromic films: Processes occurring at the Indium-Tin oxide substrate. In: IS-TCMs: 7^th International Symposium on Transparent Conductive Materials and 4^th E-MRS & MRS-J Bilateral Symposium on Advanced Oxides and Wide Bandgap Semiconductors,. Paper presented at 7^th International Symposium on Transparent Conductive Materials and 4^th E-MRS & MRS-J Bilateral Symposium on Advanced Oxides and Wide Bandgap Semiconductors, Chania Crete Greece, Oct 14-19, 2018. (pp. 215). , Article ID PS1-25.
Open this publication in new window or tab >>Enhanced durability of Tungsten oxide electrochromic films: Processes occurring at the Indium-Tin oxide substrate
2018 (English)In: IS-TCMs: 7^th International Symposium on Transparent Conductive Materials and 4^th E-MRS & MRS-J Bilateral Symposium on Advanced Oxides and Wide Bandgap Semiconductors,, 2018, p. 215-, article id PS1-25Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

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.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-369142 (URN)
Conference
7^th International Symposium on Transparent Conductive Materials and 4^th E-MRS & MRS-J Bilateral Symposium on Advanced Oxides and Wide Bandgap Semiconductors, Chania Crete Greece, Oct 14-19, 2018.
Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2018-12-17
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ORCID iD: ORCID iD iconorcid.org/0000-0003-0393-0273

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