Fernand E. Girouard

Electrolyte thickness dependence of the electrochromic behavior of ‘‘a‐WO3’’ films

The electrochromic behavior of all‐solid‐state device, Au/a‐WO3/LiF/Au has been studied as a function of the thickness of LiF as electrolyte. Thickness‐dependent coloration and response time have been observed. The electrochromic coloration takes place at different stages, and a significant change in the transmittance of the tandem over a wide wavelength range (500–1000 nm) occurs. Hence, the performance of this configuration suggests the possible application of the tandem in all‐solid‐state ‘‘switchable windows’’.

Sol-gel-prepared ITO films for electrochromic systems

Abstract Indium tin oxide (ITO) films have been prepared by the sol-gel method using both organic and inorganic precursors. A computer-controlled dip-coating unit is designed and fabricated in our laboratory for a precise control of the parameters during the dip-coating process. These films have been characterized by X-ray diffraction optical and electrical study and also by atomic absorption spectroscopy. The optimized coatings exhibit a sheet resistance of ara und 100 Ω/□ and an average visible solar transmission of around 85%. A five-layer electrochromic system using these ITO layers as transparent electrodes was fabricated and tested. The performance of the electrochromic system indicates the high potential of these films for such applications, especially for large area coaling.

Lithiation studies on some transition metal oxides for an all-solid thin film electrochromic system

A study of the lithiation behavior of some transition metal oxides has been carried out. Using a dry method of lithiation changes in optical and electrical properties of WO3, V2O5 and Nb2O5 films prepared under different conditions are studied. The optimum results and techniques are used for the fabrication of an all-solid electrochromic (EC) system based on the utilization of high coloration efficiency WO3 as the base electrochromic layer and the low coloration efficiency V2O5 as the counter electrode. LiBO2 has been used as the ion conducting layer. Such system has been operated over several hundred optical switching cycles without any degradation so far. All results indicate the suitability of the system for “smart” window application.

Reflection–transmission photoellipsometry: theory and experiments

We propose a method that uses reflection and transmission photoellipsometry to analyze samples consisting of thin films combined with semitransparent thick layers or substrates in the form of multilayer structures. Athick film or substrate is defined as a layer for which no interference effects can be observed for a given wavelength resolution, and contributions from multiple reflections in the substrate are taken into account in the theoretical treatment. An automatic reflection-transmission spectroscopic ellipsometer was built to test the theory, and satisfactory results have been obtained. Examples corresponding to a strongly absorbing film deposited on a glass substrate and a highly transmitting film also deposited on glass are shown. In both cases a good fit between theory and experiment is found. The photoellipsometric method presented is particularly suited to the analysis of actual samples of energy-efficient coatings for windows.

Optical and electrochemical properties of vanadium pentoxide gel thin films

Optical and electrochemical properties of vanadium pentoxide (V2O5) films prepared by sol‐gel method from organic and inorganic precursors were studied. The organic gel was obtained by hydrolysis and polycondensation of vanadium isopropoxide dissolved in isopropanol. The inorganic gel was prepared from aqueous solution of sodium vanadate. Lithium insertion in LiyV2O5 films (0<y≤2.0) was investigated by cyclic voltammetry and electrochemical potential spectroscopy, showing good reversibility up to y∼2.0 and structure transitions from α phase to e phase and δ phase in the range 0<y≤1.0. Highest values for chemical diffusion coefficient were about 3×10−10 cm2/s at y∼0.8, as determined from complex impedance measurements.

Structure and infrared spectra of sol—gel derived tungsten oxide thin films

Abstract FT-IR/ATR spectroscopy and transmission/reflection ellipsometry were used to study the structure and the optical properties of hydrated tungsten oxide thin films prepared by a sol—gel synthesis. The formation of the film on an internal reflection element was followed spectroscopically. Bands were assigned to WO bonds belonging to different condensed species. The close relationship between the spectral pattern, and the type and hydration state of the substrate is evidenced. The thickness and the optical properties of the hydrated tungsten oxide film were determined by transmission/reflection ellipsometry.

p‐polarized optical properties of aggregated Au films

Transmittance with p‐polarized light at oblique incidence has been measured for aggregated Au films in the region from 0.40 to 0.65 μm. At large values of the incidence angle, two minima associated with the perpendicular and parallel plasma resonances in the particles were observed. The dependence of these absorption features on film characteristics was accounted for by a simple effective medium model assuming a spheroidal shape for the particles. In this model, the substrate effect has been incorporated by mirror‐image contributions of the induced dipoles. A log‐normal distribution for the axial ratio was assumed in order to take into account the broadening of the absorption characteristics. Satisfactory agreement between theory and experiment has been obtained using only the optical thickness as a fitting parameter, and assuming a certain standard deviation for the log‐normal distribution.

Fabrication and testing of an all-solid state system for smart window application

An all-solid monolithic electrochromic (EC) system, based on tungsten oxide and vanadium pentoxide, was fabricated and tested for electrochromic performance. The system exhibits a solar transmittance modulation between around 58 and 9% and visible transmittance modulation between around 65 and 13% in the bleached and coloured states, respectively. The system was coloured and bleached for over 2000 cycles. The EC performance of the system has also been carried out under different external conditions. The possibility of the addition of an improved Li ion conductor and a protective layer is also studied. These changes seem to render the EC system more stable and faster in EC response. The results of these studies indicate a good potential of such a monolithic system for smart window application.

Study of lithium intercalation into tungsten oxide films prepared by different methods

Abstract The interaction of lithium atoms into amorphous tungsten oxide films deposited by thermal evaporation, sputtering and sol-gel synthesis is studied spectroscopically. The mechanism of insertion of lithium into the film depends on the amount and the bonding state of water to the tungsten oxide network. Thermally evaporated tungsten oxide film contains water bonded chemically in the form of a hydrogen tungsten bronze which facilitates the accommodation of a high number of lithium atoms. In the sputtered film, water is physisorbed and the lithiation is incomplete. Tungsten oxide films prepared by sol-gel synthesis have structural water molecules directly involved in the lithiation process. The formation of lithium tungstate independent of the preparation method is demonstrated.

Electrical and optical properties of Li‐doped LiBO2 and LiNbO3 films

Li‐doped LiBO2 and LiNbO3 thin films have been studied and their optical and electrical properties determined. With doping the ionic conductivity of the films was found to increase substantially. The highest conductivity obtained with the doped films was about 4.5×10−6 S cm−1. All the films exhibited a high degree of transmission in the spectral region from 350 to 2500 nm. The remarkable increase in the ionic conductivity coupled to the preservation of a high optical transmission makes this doping technique highly attractive for devising ion conductors that can be used in transmissive solid‐state electrochromic systems or the so‐called ‘‘smart windows.’’