| 51. |
- Atak, Gamze, et al.
(författare)
-
Cycling durability and potentiostatic rejuvenation of electrochromic tungsten oxide thin films : Effect of silica nanoparticles in LiClO4-Propylene carbonate electrolytes
- 2023
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier. - 0927-0248 .- 1879-3398. ; 250
-
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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| 52. |
- Atak, Gamze, et al.
(författare)
-
Electrochromic performance of WO3 films with different ITO layers
- 2019
-
Ingår i: EMRS Spring Meeting 2019..
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Electrochromic (EC) materials are able to change their optical properties such as transmission, absorption and reflection reversibly by application of an external voltage. EC metal oxides are divided into two groups: cathodic (coloring under ion insertion) and anodic (coloring under ion extraction). Tungsten oxide (WO3) is a well-known cathodic EC material and has been intensively studied in the last 30 years. EC materials and devices have been developed as an alternative to passive coating materials for light and heat management. Conventionally, an EC device is a construction with five-layers: transparent conducting oxide (TCO)/cathodic EC/ion conducting layer (liquid, gel or solid)/anodic EC/TCO, either all on one substrate or positioned between two substrates in a laminated configuration. Indium-tin oxide (ITO) coated substrates are used as a TCO electrode in EC applications due to their high conductivity and transparency.In this study, we deposited WO3 films onto ITO coated glass substrates with different sheet resistances (15, 30, 60 and 1000 Ω/□) by using DC magnetron sputtering technique. Optical and structural properties of ITO films were investigated. For durability studies, cyclic voltammetry data was 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. Chronoamperometry measurements of the WO3 films were also performed. We measured the inserted and extracted charges as well as bleaching and coloring times of WO3 films with different ITO layer properties. Generally, ITO with low resistivity is preferred for the electrochemical measurements while absorption is low in the near-infrared region for ITO with higher resistivity. In this study, it is observed that the ITO with 60 Ω/□ sheet resistance is very suitable for optical and electrochromic measurements.
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| 53. |
- Atak, Gamze, et al.
(författare)
-
Electrochromism of nitrogen-doped tungsten oxide thin films
- 2020
-
Ingår i: Materials Today. - : Elsevier BV. - 2214-7853. ; 33:6, s. 2434-2439
-
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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| 54. |
- Atak, Gamze, et al.
(författare)
-
The role of oxygen to argon gas flow ratio on the durability of sputter-deposited electrochromic tungsten oxide films
- 2021
-
Ingår i: EMRS Fall Meeting 2021.
-
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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| 55. |
- Avendano, Esteban, et al.
(författare)
-
Coloration Mechanism in Proton-Intercalated Electrochromic Hydrated NiOy and Ni1-xVxOy Thin Films
- 2009
-
Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 156:8, s. p132-p138
-
Tidskriftsartikel (refereegranskat)abstract
- Electrochromic (EC) films of nickel oxide, with and without vanadium, were prepared by reactive dc magnetron sputtering. They were characterized by electrochemical and optical measurements and studied by X-ray photoelectron spectroscopy (PES) using synchrotron radiation. The films were analyzed under as-deposited conditions and after bleaching/coloration by insertion/extraction of protons from a basic solution and ensuing charge stabilization. Optical measurements were consistent with a coloration process due to charge-transfer transitions from Ni2+ to Ni3+ states. The PES measurements showed a higher concentration of Ni3+ in the colored films. Moreover, two peaks were present in the O 1s spectra of the bleached film and pointed to contributions of Ni(OH)(2) and NiO. The changes in the O 1s spectra upon coloration treatment indicate the presence of Ni2O3 in the colored film and necessitated an extension of the conventional model for the mechanism of EC coloration. The model involves not only proton extraction from nickel hydroxide to form nickel oxyhydroxide but also participation of NiO in the coloration process to form Ni2O3.
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| 56. |
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| 57. |
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| 58. |
- Backholm, Jonas, et al.
(författare)
-
Determination of solid phase chemical diffusion coefficient and density of states by electrochemical methods : Application to iridium oxide-based thin films
- 2008
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:2, s. 023702-
-
Tidskriftsartikel (refereegranskat)abstract
- Potentiostatic intermittent titration technique (PITT) and electrochemical impedance spectroscopy (EIS) were investigated as methods to determine solid phase chemical diffusion coefficient (D) and electronic density of states (DOS). These techniques were then applied to iridium oxide (IrOx) and iridium-tantalum oxide (IrTaOx) thin films prepared by sputter deposition. The experiments, performed in 1M propionic acid between -0.2 and 0.8 V vs Ag/AgCl, showed effects of interfacial side reactions, whose contribution to the electrochemical response could be identified and corrected for in the case of PITT as well as EIS. It was found that D is strongly underestimated when using PITT with the common Cottrell formalism, which follows from non-negligible interfacial charge transfer and Ohmic resistances. EIS indicated an anomalous diffusion mechanism, and D was determined to be in the 10(-11)-10(-10) cm(2)/s range for IrOx and IrTaOx. Both PITT and EIS showed that the intercalated charge as a function of potential exhibits a shape that resembles the theoretical DOS of crystalline iridium oxide, especially for IrTaOx.
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| 59. |
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| 60. |
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| 61. |
- Backholm, Jonas, 1977-
(författare)
-
Electrochromic Properties of Iridium Oxide Based Thin Films
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electrochromic iridium oxide (IrOx) and iridium-tantalum oxide (IrTaOx) thin films were prepared by reactive magnetron sputtering. Composition, density, and structure were determined using Rutherford backscattering spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and electron energy loss spectroscopy. The electronic density of states (DOS) and the solid phase chemical diffusion coefficient (D) were determined for hydrogen in IrOx and IrTaOx by potentiostatic intermittent titration technique (PITT), and electrochemical impedance spectroscopy (EIS). The complex refractive indices were determined for colored and bleached IrOx and IrTaOx by inverting transmission and reflectance, measured using spectrophotometry in the 300-2500 nm wavelength range. A very porous structure, with a stoichiometry of IrO2.2, was found for IrOx. It contained ~4 nm sized grains. The IrTaOx had a denser structure built up by ~4 nm sized grains. The composition of IrTaOx was found to vary on a nanometer scale, with an average composition of IrTa1.4O5.6. It was found that DOS can be measured using PITT and EIS in the presence of spontaneous side reactions, even for systems influenced by non-negligible charge transfer kinetics and Ohmic drops. It was found that the measured DOS is 30-50% of the theoretically calculated DOS and that D is in the 10-10 – 10-11 cm2/s range for both materials. The hydrogen diffusion mechanism was described by an anomalous diffusion model, possibly indicating percolation or diffusion paths described by a fractal network. The refractive indices were found to be ~1.3 and ~2 for IrOx and IrTaOx, respectively, and independent of coloration state, whereas the extinction coefficients were found to modulate by ~30% for IrOx and ~50% for IrTaOx, making IrTaOx more favorable for electrochromic applications. A modulation peak was found at ~660 nm for both IrOx and IrTaOx associated with the removal of intraband transitions within the Ir t2g band.
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| 62. |
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| 63. |
- Backholm, Jonas, et al.
(författare)
-
Iridium-based oxides: Recent advances in coloration mechanism, structural and morphological characterization
- 2008
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 92:2, s. 91-96
-
Tidskriftsartikel (refereegranskat)abstract
- Films of iridium-tantalum oxide and iridium oxide have been prepared by sputtering and studied regarding their structure and electrochemical properties. X-ray diffraction and transmission electron microscopy showed an average grain size of 3-4 nm for both films. Point energy dispersive X-ray spectrometry showed an inhomogeneous distribution of iridium and tantalum indicating that the iridium-tantalum oxide may be a mixture of small IrO2 and Ta2O5 grains, which is consistent with the determined composition IrTa1.4O5.6. X-ray photoelectron spectroscopy gave valuable information on the stabilization process of the as-deposited films involving an uptake of oxygen, and on a coloration mechanism only including protons.
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| 64. |
- Backholm, Jonas, et al.
(författare)
-
Optical properties of electrochromic iridium oxide and iridium-tantalum oxide thin films in different colouration states
- 2008
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 92:11, s. 1388-1392
-
Tidskriftsartikel (refereegranskat)abstract
- Electrochromic iridium oxide (IrOx) and iridium-tantalum oxide (IrTaOx) thin films were prepared by sputtering. Complex refractive indices were determined for samples deposited on indium-tin oxide covered glass in different colouration states, and for as-deposited samples on sapphire and Corning glass. The refractive index was found to be practically constant for both IrOx (similar to 1.3) and IrTaOx (similar to 2). The extinction coefficient was found to vary between the coloured and bleached states with similar to 35% for IrOx and similar to 55% for IrTaOx at 660 nm. This is believed to be a result of the removal of intraband transitions within the Ir t(2g) band during bleaching.
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| 65. |
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| 66. |
- Barrios, David, et al.
(författare)
-
Determination of the optical constants of the active layer of a suspended particle device smart window with multilayer structure at the clear and dark states, with and without applied voltage.
- 2018
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Smart windows based on suspended particle devices (SPDs) are able to switch optically from dark to clear visual appearance when applying an AC electrical signal. This effect is due to light absorbing nanoparticles that get aligned by the applied voltage. The sandwich structure of a SPD consist of several layers and includes two outer glass substrates, each one covered on its inwards-facing side with a transparent conducting thin layer surrounding the centrally positioned SPD active layer. A knowledge of the optical constants of each layer—i.e., the complex refractive index, including its real and imaginary (absorption and scattering) parts—is a key in the design of the visual appearance of the SPD window and is a useful tool to determine the optimum thickness of the active layer.
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| 67. |
- Barrios, David, et al.
(författare)
-
Inversion of two-flux and four-flux radiative transfer models for determining scattering and absorption coefficients for a suspended particle device
- 2019
-
Ingår i: Applied Optics. - : OPTICAL SOC AMER. - 1559-128X .- 2155-3165. ; 58:32, s. 8871-8881
-
Tidskriftsartikel (refereegranskat)abstract
- Intrinsic and extrinsic scattering and absorption coefficients of a suspended particle device (SPD) smart window sample at dark and dear appearance states-without and with applied electrical voltage, respectively-were determined by means of the Maheu, Letoulouzan, and Gouesbet four-flux (intrinsic) and Kubelka-Munk two-flux ( extrinsic) radiative transfer models, respectively. Extrinsic values were obtained from fitting to the two-flux model taking into account the predominantly forward scattering of the SPD. As an approximation, the Fresnel reflection coefficients were integrated out to the critical angle of total internal reflection in order to compute diffuse interface reflectances. Intrinsic coefficients were retrieved by adding a new proposed approximation for the average crossing parameter based on the collimated and diffuse light intensities at each interface. This approximation, although an improvement of previous approaches, is not entirely consistent with the two-flux model results. However, it paves the way for further development of methods to solve the inverse problem of the four-flux model.
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| 68. |
- Barrios, David, et al.
(författare)
-
Light Scattering Parameters of Polymer Dispersed Liquid Crystals Obtained by Inversion of Experimental Data
- 2022
-
Ingår i: Proceedings of the Bremen Zoom Workshop on Light Scattering 2022. - : Leibniz Institute for Materials Engineering IWT. ; , s. 8-11
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Polymer Dispersed Liquid Crystal (PDLC) devices are electrically controlled smart windows, that switch from a translucent milky appearance (off state) to a transparent clear appearance (on state). We have studied the intrinsic and extrinsic scattering and absorption coefficients obtained by inversion of spectrophotometric transmittance and reflectance data. The inversion procedure uses two flux and four flux models and similar approximations for the average crossing parameter (ACP) as in our previous workon suspended particle devices [1]. Good fits are obtained, but the ACP approximation was found to be inconsistent with fitted parameters.
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| 69. |
- Barrios, David, et al.
(författare)
-
Simulation of the thickness dependence of the optical properties of suspended particle devices
- 2015
-
Ingår i: Solar Energy Materials and Solar Cells. - 0927-0248 .- 1879-3398. ; 143, s. 613-622
-
Tidskriftsartikel (refereegranskat)abstract
- Suspended particle devices (SPDs) constitute an electrically powered chromogenic technology, in which the active layer quickly are able to rapidly switches from a dark bluish-black dark color state to a clear greyish color appearance when an AC electric field is applied. Two-flux and four-flux models were used to derive refractive indices and extinction coefficients, as well as scattering and absorption coefficients, of the particle-containing active layer. These entities were used in model calculations to predict the direct, total and diffuse components of the transmittance andthe reflectance, together along with the color appearance and haze, as a function of the thickness of the active layer. An optimum thickness for the optical contrast of the SPD was determined in this way and was found to be in the range of 200 to 300 nm. The SPDdevices device exhibits a significant reflectance haze particularly in reflection.
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| 70. |
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| 71. |
- Barrios, David, et al.
(författare)
-
Toward a quantitative model for suspended particle devices : Optical scattering and absorption coefficients
- 2013
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 111, s. 115-122
-
Tidskriftsartikel (refereegranskat)abstract
- Suspended particle devices (SPDs) allow rapid voltage-controlled modulation of their optical transmittance and are of interest for solar-energy-related and other applications. We investigated the spectral total and diffuse transmittance of an SPD, including its angular dependence. The optical modulation was large for visible light but almost nil in the infrared, and the devices had noticeable haze. A theoretical two-flux model was formulated and provided a quantitative description of the absorption and scattering coefficients and thereby of the detailed optical performance. This analysis gives a benchmark for assessing improvements of the SPD technology as well as for comparing it with alternative technologies for optical modulation.
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| 72. |
- Bayrak Pehlivan, I., et al.
(författare)
-
A polymer electrolyte with high luminous transmittance and low solar throughput : Polyethyleneimine-lithium bis(trifluoromethylsulfonyl) imide with In2O3:Sn nanocrystals
- 2012
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:24, s. 241902-
-
Tidskriftsartikel (refereegranskat)abstract
- Chemically prepared similar to 13-nm-diameter nanocrystals of In2O3:Sn were included in a polyethyleneiminelithium bis(trifluoromethylsulfonyl) imide electrolyte and yielded high haze-free luminous transmittance and strong near-infrared absorption without deteriorated ionic conductivity. The optical properties could be reconciled with effective medium theory, representing the In2O3:Sn as a free electron plasma with tin ions screened according to the random phase approximation corrected for electron exchange. This type of polymer electrolyte is of large interest for opto-ionic devices such as laminated electrochromic smart windows.
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| 73. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
-
Bifunctional solar electrocatalytic water splitting using CIGS solar modules and WO3-based electrolyzers
- 2019
-
Ingår i: EMRS Spring Meeting 2019.
-
Konferensbidrag (refereegranskat)abstract
- Using energy from the sun to produce a fuel and finally obtaining only water as an exhaust is a promising future technology for renewable energy and environmental sustainability. Solar driven water splitting is a method to produce hydrogen from solar energy. Coupling a solar cell with an electrolyzer is the approach with highest technological readiness. CuInxGa1-xSe2 (CIGS) is here a promising solar cell material for water splitting because it is possible to tune the band gap between 1.0 and 1.7 eV by changing the ratio between Ga and In, thus enabling maximum power point matching with an electrolyzer. Tungsten oxide is known as a photocatalytic material and mainly used for the oxygen evolution reaction in a water splitting process. However, WO3 films also show electrochromic activity together with hydrogen evolution. This result is interesting because it shows that WO3 films can be used as bifunctional materials for both hydrogen and oxygen evolution in water splitting, and provide additional functionalities to the system. In this study, WO3 films coated at different sputtering conditions on Ni foam and indium tin oxide substrates were investigated in the potential range of the hydrogen evolution reaction. The best overpotential of 164 mV vs. RHE at 10 mA/cm2 was obtained for WO3 films on Ni foam in 0.5 M H2SO4. The lowest potential needed for 10 mA/cm2 was measured 1.768 V for the electrolyzers consisting WO3 films on Ni foam as the cathode and non-coated Ni foam as the anode. Optimum solar-to-hydrogen (STH) efficiency of the CIGS solar cell modules and the electrolyzers was examined for different band gaps of the CIGS modules and sputtering conditions of WO3 films. Operation points of the combined system were calculated from the intersection of the voltage-current density curves for the CIGS modules and the electrolyzers. The results showed that the detailed sputtering conditions were not very critical to obtain high STH efficiency, indicating that the system could be robust and easily manufactured. The best-matched band gap of the CIGS was 1.19 eV and the highest STH efficiency of the CIGS driven WO3-based electrolyzers was 12.98 %.
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| 74. |
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| 75. |
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| 76. |
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| 77. |
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| 78. |
- Bayrak Pehlivan, İlknur
(författare)
-
Functionalization of polymer electrolytes for electrochromic windows
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Saving energy in buildings is of great importance because about 30 to 40 % of the energy in the world is used in buildings. An electrochromic window (ECW), which makes it possible to regulate the inflow of visible light and solar energy into buildings, is a promising technology providing a reduction in energy consumption in buildings along with indoor comfort. A polymer electrolyte is positioned at the center of multi-layer structure of an ECW and plays a significant role in the working of the ECW.In this study, polyethyleneimine: lithium (bis(trifluoromethane)sulfonimide (PEI:LiTFSI)-based polymer electrolytes were characterized by using dielectric/impedance spectroscopy, differential scanning calorimetry, viscosity recording, optical spectroscopy, and electrochromic measurements.In the first part of the study, PEI:LiTFSI electrolytes were characterized at various salt concentrations and temperatures. Temperature dependence of viscosity and ionic conductivity of the electrolytes followed Arrhenius behavior. The viscosity was modeled by the Bingham plastic equation. Molar conductivity, glass transition temperature, viscosity, Walden product, and iso-viscosity conductivity analysis showed effects of segmental flexibility, ion pairs, and mobility on the conductivity. A connection between ionic conductivity and ion-pair relaxation was seen by means of (i) the Barton-Nakajima-Namikawa relation, (ii) activation energies of the bulk relaxation, and ionic conduction and (iii) comparing two equivalent circuit models, containing different types of Havriliak-Negami elements, for the bulk response.In the second part, nanocomposite PEI:LiTFSI electrolytes with SiO2, In2O3, and In2O3:Sn (ITO) were examined. Adding SiO2 to the PEI:LiTFSI enhanced the ionic conductivity by an order of magnitude without any degradation of the optical properties. The effect of segmental flexibility and free ion concentration on the conduction in the presence of SiO2 is discussed. The PEI:LiTFSI:ITO electrolytes had high haze-free luminous transmittance and strong near-infrared absorption without diminished ionic conductivity. Ionic conductivity and optical clarity did not deteriorate for the PEI:LiTFSI:In2O3 and the PEI:LiTFSI:SiO2:ITO electrolytes.Finally, propylene carbonate (PC) and ethylene carbonate (EC) were added to PEI:LiTFSI in order to perform electrochromic measurements. ITO and SiO2 were added to the PEI:LiTFSI:PC:EC and to a proprietary electrolyte. The nanocomposite electrolytes were tested for ECWs with the configuration of the ECWs being plastic/ITO/WO3/polymer electrolyte/NiO (or IrO2)/ITO/plastic. It was seen that adding nanoparticles to polymer electrolytes can improve the coloring/bleaching dynamics of the ECWs.From this study, we show that nanocomposite polymer electrolytes can add new functionalities as well as enhancement in ECW applications.
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| 79. |
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| 80. |
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| 81. |
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| 82. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
-
Ion conduction of branched polyethyleneimine-lithium bis(trifluoromethylsulfonyl) imide electrolytes
- 2011
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 57, s. 201-206
-
Tidskriftsartikel (refereegranskat)abstract
- Ionic conductivity of polymer electrolytes containing branched poly (ethylene imine) (BPEI) and lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI) was measured between temperatures of 20 and 70◦C and molar ratios of 20:1 and 400:1. The electrolytes were characterized by impedance spectroscopy, differential scanning calorimetry, and viscosity measurements. At room temperature, the maximum conductivity was 2×10−6 S/cm at a molar ratio of 50:1. The molar conductivity of the electrolytes displayed first a minimum and then a maximum upon increasing salt concentration. A proportionality of molar conductivity to segmental mobility was seen from glass transition temperature and viscosity measurements. Analysis of the Walden product and isoviscosity conductivity showed that the percentage of ions bound in ion pairs increased at low concentrations below 0.1 mol/kg. The average dipole moment decreased with salt concentration. The temperature dependence of the ionic conductivity showed an Arrhenius behavior.
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| 83. |
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| 84. |
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| 85. |
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| 86. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
-
[PEI-SiO2]:[LiTFSI] nanocomposite polymer electrolytes : Ion conduction and optical properties
- 2012
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 98, s. 465-471
-
Tidskriftsartikel (refereegranskat)abstract
- Ion conductivity and optical properties were investigated for polymer electrolytes based on poly (ethyleneimine) and lithium bis(trifluoromethylsulfonyl)imide and also containing up to 9 wt.% of 7-nm-diameter SiO2 nanoparticles. The [N]:[Li] molar ratio was kept constant at 50:1. Impedance measurements were performed in the frequency range 10(-2)-10(7) Hz and between the temperatures 20 and 70 degrees C with an applied ac voltage of 1 V. Spectrophotometric data of total and diffuse transmittance were taken between the wavelengths 300 and 2500 nm. The bulk impedance was fitted to a conductive Havriliak-Negami circuit model. The ion conductivity increased monotonically for increasing SiO2 contents: specifically its room temperature value went from 8.5 x 10(-7) S/cm without nanoparticles to 3.8 x 10(-5) S/cm for 8 wt.% of SiO2 while the diffuse transmittance remained at similar to 1% so that optical clarity prevailed.
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| 87. |
- Berggren, Lars, et al.
(författare)
-
Electrical Conductivity as a Function of Temperature in Amorphous Lithium Tungsten Oxide
- 2004
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 84:1, s. 329-336
-
Tidskriftsartikel (refereegranskat)abstract
- Tungsten oxide is a widely used electrochromic material for smart windows. In order to study the charge carriers involved in the electrochromic process, it is important to characterize the electrical transport in tungsten oxide. Substoichiometric amorphous tungsten oxide films were prepared by DC-magnetron sputtering. The films were electrochemically intercalated with lithium. The Li/W intercalation ratios for the tungsten oxide films were in the range 0.15–0.53. Temperature dependent resistivity measurements were performed in the temperature range 77–300 K for samples at different lithium intercalation levels. It was found that the data are consistent with the variable range hopping model.
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| 88. |
- Berggren, Lars, et al.
(författare)
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Influence of sputtering conditions on the solar and luminous optical properties of amorphous LixWoy thin films
- 2005
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 85:4, s. 573-586
-
Tidskriftsartikel (refereegranskat)abstract
- Thin films of amorphous tungsten oxide were deposited by sputtering onto glass substrates coated by conductive indium–tin oxide. The films were sputtered at different oxygen-to-argon flow ratios with different pressure and power. Elastic recoil detection analysis determined the density and the stoichiometry. X-ray diffraction measurements showed that the films were amorphous. The films were electrochemically intercalated with lithium ions. At several intercalation levels of each film, the optical reflectance and transmittance were measured in the wavelength range 0.3–2.5 μm. We study the effect of various sputtering conditions on the coloration efficiency of the films and on the luminous and solar optical properties. The O2/Ar ratio and the sputter pressure determine to a large extent the optical absorption. As-deposited sputtered tungsten oxide with sufficiently little oxygen exhibits an absorption peak similar to the case of lithium intercalation.
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| 89. |
- Berggren, Lars, et al.
(författare)
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Optical Absorption and Durability of Sputtered Amorphous Tungsten Oxide Films
- 2003
-
Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738 .- 1872-7689. ; 165:1-4, s. 51-58
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous tungsten oxide films were made by sputtering onto glass substrates that were coated with conductive tin doped indium oxide (ITO). The films were deposited at different O2/Ar gas flow ratios and different substoichiometric compositions was determined by Elastic recoil detection analysis (ERDA). Substoichiometric as-deposited tungsten oxide is transparent above a particular oxygen content and is blue below that content. This indicates that there are at least two kinds of defects in the substoichiometric films. The oxygen vacancies may be coupled to W5+ sites, giving rise to strong absorption, or to (W–W)10+ complexes in the transparent films. Lithium ions were electrochemically intercalated at several charge levels. At each level the transmittance and reflectance were measured in the wavelength range between 0.3 and 2.5 μm. We show that as-deposited blue films and intercalated transparent films display similarly shaped optical absorption bands. Electrochromic devices were made by laminating the tungsten oxide films with sputtered Ni–V oxide deposited on ITO-coated plastic substrates. The durability under electrochemical cycling was best for the case of very substoichiometric WO2.63 films.
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| 90. |
- Berggren, Lars, 1967-
(författare)
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Optical Absorption and Electrical Conductivity in Lithium Intercalated Amorphous Tungsten Oxide Films
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Optical and electrical properties of electrochemically lithium ion intercalated thin films of x-ray amorphous tungsten oxide made by magnetron sputtering on glass substrates coated with a thin layer of conductive tin doped indium oxide, have been studied. The composition and the density of the films were characterized by the ion beam analysis methods Rutherford Backscattering Spectroscopy and Elastic Recoil Detection Analysis. The optical properties, transmittance and reflectance were investigated by spectophotometry in the wavelength range 300-2500 nm. The absorption coefficients were calculated at different lithium intercalation levels. It was found that the absorption coefficient in an as-deposited blue film has a similar asymmetric shape as for films intercalated to a Li/W ratio of ~0.03. It was possible to electrochemically bleach this film to transparency. Stoichiometric films show optical irreversibility between the bleached and the colored state in the first cycle. A polaron absorption model has been compared to the absorption coefficient for films of different intercalation levels. An increase in the Fermi level and in the polaron band width, and a nearly constant activation energy was found as the Li/W value increased. The radius of the polaron wavefunction for different lithium intercalation levels and film compositions has been estimated from electrical measurements. The total absorption coefficient has been compared to the site-saturation model. The model is good for films intercalated in the optically reversible region. A modified site-saturation model that could be applied also in the optically irreversible region and involves electron transitions between W6+, W5+ and W4+ sites, has also been compared to experimental values. It was found that the total absorption, optical density and the coloration efficiency is higher for the WO2.63 film than in the less oxygen deficient films and that this film is optically more durable in an electrochemically cyclic lifetime device test.
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| 91. |
- Berggren, Lars, et al.
(författare)
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Optical absorption in lithiated tungsten oxide thin films : Experiment and theory
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 102:8, s. 083538-
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous tungsten oxide exhibits electrochromism when intercalated with protons, lithium, sodium, and other ions. Thin films of the material were prepared by dc magnetron sputtering and then electrochemically intercalated with lithium. The optical absorption in the wavelength range of 300-2500 nm was measured for a number of lithium concentrations. The optical absorption shows a maximum for lithium/tungsten ratios of 0.3-0.5. The optical spectra can be fitted by a superposition of three Gaussian peaks, representing the three possible electronic transitions between W6+, W5+, and W4+ sites. The variation of the peak strength with lithium concentration is consistent with an extended site-saturation theory.
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| 92. |
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| 93. |
- Berggren, Lars, et al.
(författare)
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Optical Charge Transfer Absorption in Lithium-intercalated Tungsten Oxide Thin Films
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; :88, s. 081906-
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous tungsten oxide exhibits electrochromism when intercalated with protons or lithium ions.Thin films of the material were prepared by dc magnetron sputtering and subsequentlyelectrochemically intercalated with lithium. The optical absorption in the wavelength range300 to 2500 nm was measured for a number of lithium concentrations. All the spectra can be fittedby a superposition of three Gaussian peaks, representing the three possible electronic transitionsbetween W6+, W5+, and W4+ sites. The variation of the peak strength with lithium concentration isconsistent with the predictions of a statistical theory.
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| 94. |
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| 95. |
- Berggren, Lars, et al.
(författare)
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Polaron Absorption in Amorphous Tungsten Oxide Films
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 90, s. 1860-1863
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous thin films of tungsten oxide were deposited by sputtering onto glass substrates covered by conductive indium–tin oxide. The density and stoichiometry were determined by Rutherford backscattering spectrometry. Lithium ions were intercalated electrochemically into the films. The optical reflectance and transmittance were measured in the wavelength range from 0.3 to 2.5 μm, at a number of intercalation levels. The polaron absorption peak becomes more symmetric and shifts to higher energies until an intercalation level of 0.25 to 0.3 Li+/W, where a saturation occurs. The shape of the polaron peak is in very good agreement with the theory of Bryksin [Fiz. Tverd. Tela 24, 1110 (1982)]. Within this model, the shift of the absorption peak is interpreted as an increase in the Fermi level of the material as more Li ions are inserted.
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| 96. |
- Cindemir, Umut, et al.
(författare)
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Fluctuation-enhanced and conductometric gas sensing with nanocrystalline NiO thin films : A comparison
- 2017
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Ingår i: Sensors and actuators. B, Chemical. - : Elsevier BV. - 0925-4005 .- 1873-3077. ; 242, s. 132-139
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Tidskriftsartikel (refereegranskat)abstract
- Nanocrystalline thin films of NiO were prepared by advanced reactive gas deposition, and their responses to formaldehyde, ethanol and methane gases were studied via fluctuation-enhanced and conductometric methods Thin films with thicknesses in the 200–1700-nm range were investigated in as-deposited form and after annealing at 400 and 500◦C. Morphological and structural analyses showed porous deposits with NiO nanocrystals having face-centered cubic structure. Quantitative changes in frequency-dependent resistance fluctuations as well as in DC resistance were recorded upon exposure to formaldehyde, ethanol and methane at 200◦C. The response to formaldehyde was higher than that to ethanol while the response to methane was low, which indicates that the NiO films exhibit significant selectivity towards different gaseous species. These results can be reconciled with the fact that formaldehyde has a nucleophilic group, ethanol is an electron scavenger, and methane is hard to either reduce or oxidize. The gas-induced variations in DC resistance and resistance fluctuations were in most cases similar and consistent.
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| 97. |
- Cindemir, Umut, et al.
(författare)
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Nickel oxide thin film sensor for fluctuation-enhanced gas sensing of formaldehyde
- 2015
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Ingår i: 2015 IEEE Sensors. - 9781479982035
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Konferensbidrag (refereegranskat)abstract
- Nanocrystalline nickel-oxide-based thin films were prepared by advanced reactive gas deposition, and the response of these films to formaldehyde was studied by fluctuation-enhanced sensing. Morphological and structural analyses showed porous deposits of nickel oxide particles with face-centered cubic structure. Resistance fluctuations were measured upon exposure to ethanol, formaldehyde and methane at 200 degrees C. Power density spectra were used to quantify the response. The response to formaldehyde was higher than to ethanol at 200 degrees C, and no significant response was observed for methane thus demonstrating some gas-species selectivity.
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| 98. |
- Cindemir, Umut, et al.
(författare)
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Porous Nickel Oxide Sensor for Formaldehyde Detection
- 2014
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Ingår i: European Materials Society (E-MRS) Spring Meeting, Lille, France, May 26-30, 2014..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Formaldehyde is a volatile organic compound, which is a harmful indoor pollutant, causing sick building syndrome (SBS) and is released from household and building materials. Since higher concentrations of formaldehyde are considered to be carcinogenic, monitoring them indoors is of great importance. Advanced gas deposition has here been used to fabricate highly porous nickel oxide (NiO) thin films for formaldehyde sensing. The films were deposited on Al2O3 substrates with prefabricated comb-structured electrodes, and a resistive heater at the opposite face. The morphology of the films was investigated with scanning electron microscopy, and the porosity was determined by nitrogen adsorption isotherms with the Brunauer-Emmett-Teller method. The particle size was found to be less than 10 nm, as determined by x-ray diffraction. X-ray photoelectron spectroscopy of the NiO films was also done. Gas sensing measurements were done using a total gas flow rate of 200 ml/min. Resistivity values of sensors were recorded with formaldehyde diluted in synthetic air. Sensor resistances were recorded at 50 ppm, 25ppm, 10ppm and 5 ppm formaldehyde concentration. NiO films showed promising formaldehyde gas sensing properties implying lower levels of detection limit.
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| 99. |
- Cindemir, Umut, et al.
(författare)
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Sputter-Deposited Indium-Tin Oxide Thin Films for Acetaldehyde Gas Sensing
- 2016
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Ingår i: Coatings. - : MDPI AG. - 2079-6412. ; 6:2
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Tidskriftsartikel (refereegranskat)abstract
- Reactive dual-target DC magnetron sputtering was used to prepare In-Sn oxide thin films with a wide range of compositions. The films were subjected to annealing post-treatment at 400 degrees C or 500 degrees C for different periods of time. Compositional and structural characterizations were performed by X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Rutherford backscattering and scanning electron microscopy. Films were investigated for gas sensing at 200 degrees C by measuring their resistance response upon exposure to acetaldehyde mixed with synthetic air. We found that the relative indium-to-tin content was very important and that measurable sensor responses could be recorded at acetaldehyde concentrations down to 200 ppb, with small resistance drift between repeated exposures, for both crystalline SnO2-like films and for amorphous films consisting of about equal amounts of In and Sn. We also demonstrated that it is not possible to prepare crystalline sensors with intermediate indium-to-tin compositions by sputter deposition and post-annealing up to 500 degrees C.
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| 100. |
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