| 1. |
- Atak, Gamze, et al.
(författare)
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Durability studies of annealed electrochromic tungsten oxide films
- 2021
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Ingår i: EMRS Fall Meeting 2021.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In electrochromic (EC) applications, annealing is a crucial parameter not only for an individual layer but also for a full device. For the fabrication of a complete EC device, indium tin oxide (ITO) is often preferred as a transparent conductor layer. ITO films with high transparency and low electrical resistance are usually obtained by sputtering at high substrate temperatures. Consequently, the effect of high temperature on the EC layers can be very significant during sputtering of the ITO top layer for EC devices consisting of five sputtered layers on a single substrate. The role of annealing of a single layer of WO3 may also be important for EC performance. In the present work, we studied the effects of annealing on the durability of WO3 films. Thin films of WO3 were deposited by reactive DC magnetron sputtering in a mixture of Ar and O2 gases using an oxygen to argon ratio of 0.15. The total gas pressure was set to 4.0 Pa, and the sputtering power was 200 W. The WO3 films were deposited onto (i) unheated glass plates, (ii) such plates pre-coated with transparent and electrically conducting ITO with a sheet resistance of 60 Ω/square, and (iii) glass plates pre-coated with fluorine-doped tin oxide (FTO) with a sheet resistance of 14 Ω/square. Film thicknesses were 300±10 nm. After deposition of the films, the samples were annealed at 150, 300, 450, and 600 °C in ambient air for one h using a heating rate of 10 °C min-1. Cyclic voltammetry (CV) was performed for up to 500 cycles between 2.0 and 4.0 V vs. Li/Li+ at a scan rate of 20 mV s–1. Annealing at temperatures at and above 300 °C resulted in deteriorated electrochromic properties of the WO3 films i.e., a decreased transmittance variation. Charge density and coloration efficiency changes during extended electrochemical cycling were also observed as a function of cycle number and annealing temperature. It was found that the maximum optical transmittance modulation at a wavelength of 528 nm after 500 CV cycles was 69.3% for the film annealed at 150 °C.
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| 2. |
- Atak, Gamze, et al.
(författare)
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Electrochromic tungsten oxide films prepared by sputtering : Optimizing cycling durability by judicious choice of deposition parameters
- 2021
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Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 367
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of W oxide were prepared by reactive DC magnetron sputtering (5 cm-diameter W target), and their electrochromic (EC) properties were investigated in an electrolyte of LiClO4 in propylene carbonate. The purpose of the study was to elucidate the role of critical deposition parameters-oxygen/argon gas flow ratio for the sputter plasma Gamma, total pressure in the sputter plasma p(tot) , and sputtering power P-s - on the EC performance with foci on electrochemical cycling durability and optical modulation range Delta T. Specifically, we used 0.15 <= Gamma <= 0.90, 5 <= p(tot) <= 30 mTorr, and 200 <= P-s <= 400 W and studied cycling durability for up to 500 voltammetric cycles in the range 2.0-4.0 V vs. Li/Li+ together with optical properties at a wavelength of 528 nm. Most significantly, we discovered that a judicious choice of deposition parameters could yield films with superior cycling durability. Thus a similar to 300 nm-thick film prepared at Gamma = 0.90, p(tot) = 10 mTorr, and P-s = 200 W showed Delta T approximate to 65% after an initial "training" during similar to 100 voltammetric cycles; higher values of p(tot), on the other hand, yielded films whose Delta Ts degraded by similar to 10% during the cycling, and a lower value of p(tot) led to dark films with only marginal electrochromism. Hence our work delineates a pathway towards W oxide films with excellent durability of the EC properties.
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| 3. |
- Atak, Gamze, et al.
(författare)
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The role of oxygen to argon gas flow ratio on the durability of sputter-deposited electrochromic tungsten oxide films
- 2021
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Ingår i: EMRS Fall Meeting 2021.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Materials that are able to vary their transparency and coloration reversibly when they are subjected to an electrical current or voltage are referred to as “electrochromic” (EC). High optical transmittance modulation and long service lifetime are apparent requirements for EC materials used in smart windows technology. An extended service lifetime is provided by the long-term durability of the materials. One important aspect of durability is the ability to sustain charge transport between the EC film and electrolyte, or between the two EC films in a device, for many hundreds or thousands of cycles without any significant changes in the performance such as optical modulation and inserted-extracted charge. The purpose of this study is to clarify the effects of the oxygen-argon gas flow ratio during sputter deposition on the durability of WO3 films. In this study, the oxygen to argon gas-flow ratio was modulated by setting the O2 flow rate to 7.5, 15.0, 22.5, and 45.0 ml min-1 and using a fixed Ar flow rate of 50 ml min-1. Thus, the oxygen to argon gas-flow ratio was varied from 0.15 to 0.90. The pressure in the sputter plasma was set as 30 mTorr and the sputter power was maintained at 200 W. For durability studies, cyclic voltammetry data were recorded for up to 500 cycles between 2.0 and 4.0 V versus Li/Li+ at a scan rate of 20 mV s-1. High oxygen to argon gas ratio was found to have a positive effect on the EC properties of the films. When the long-term performance of the films was examined, it was seen that all the samples displayed a slow decline of the colored-state transmittance due to ion accumulation in the host material. After 500 color-bleach cycles, the maximum optical transmittance modulation between colored and bleached states at a wavelength of 528 nm was 63.6% when the oxygen to argon gas-flow ratio was 0.90.
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| 4. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
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Electrochromic solar water splitting using a cathodic WO3 electrocatalyst
- 2021
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Ingår i: Nano Energy. - : Elsevier. - 2211-2855 .- 2211-3282. ; 81
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Tidskriftsartikel (refereegranskat)abstract
- Solar-driven water splitting is an emerging technology with high potential to generate fuel cleanly and sustainably. In this work, we show that WO3 can be used as a cathodic electrocatalyst in combination with (Ag,Cu) InGaSe2 solar cell modules to produce hydrogen and provide electrochromic functionality to water splitting devices. This electrochromic effect can be used to monitor the charge state or performance of the catalyst for process control or for controlling the temperature and absorbed heat due to tunable optical modulation of the electrocatalyst. WO3 films coated on Ni foam, using a wide range of different sputtering conditions, were investigated as cathodic electrocatalysts for the water splitting reaction. The solar-to-hydrogen (STH) efficiency of solar-driven water electrolysis was extracted using (Ag,Cu)InGaSe2 solar cell modules with a cell band gap varied in between 1.15 and 1.25 eV with WO3 on Ni foam-based electrolyzers and yielded up to 13% STH efficiency. Electrochromic properties during water electrolysis were characterized for the WO3 films on transparent substrate (indium tin oxide). Transmittance varied between 10% and 78% and the coloration efficiency at a wavelength of 528 nm and the overpotential of 400 mV was 40 cm(2) C-1. Hydrogen ion consumption in ion intercalation for electrochromic and hydrogen gas production for water electrolysis processes was discussed.
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