A Review On WO3 Films Prepared By Various Methods

DOI: 10.17571/appslett.2015.01026
Appl. Sci. Lett. 1(4) 2015, 115-124 www.appslett.com Copyright 2015 Asian Scientific Publishers 115
Appl. Sci. Lett. 1(4) 2015, 115-124
Applied Science Letters
REVIEW ARTICLE
www.appslett.com
An interdisiplinary peer-reviewed international journal
A Review on WO3 films prepared by various methods
Vyomesh R. Buch 1,3*
, Amit Kumar Chawla 2
, Sushant K Rawal3
1Department of Mechanical Engineering, Babaria Institute of Technology, Varnama, Vadodara -391240, Gujarat, India
2Institute of Nanoscience and Nanotechnology, University of Petroleum and Energy Studies, Energy Acres, Dehradun-248 007,
Uttarakhand, India
3CHAMOS Matrusanstha Department of Mechanical Engineering, Chandubhai S. Patel Institute of Technology, Charotar University
of Science and Technology (CHARUSAT), Changa-388421, India
(Received 07 July, 2015; accepted 05August 2015; published 01 October, 2015)
Recent developments in the synthesis of transition metal oxides in the form of thin films have opened up opportunities in the construction of
electrochromic devices with enhanced properties. Transition metal oxides like WO3 and MoO3 have good electrochromic properties and these
oxides can also change their optical properties when a voltage pulse is applied. These electrochromic materials are used for displays, gas
sensors, rear-view mirrors and smart windows for energy saving applications. There are numbers of different techniques used for the
deposition of stable thin films of these oxide materials. Tungsten Oxide (WO3) is the best suited material for energy conservation applications.
Thin films of WO3 are deposited by various techniques that offers flexibility, allows the fabrication of required topographical, physical,
crystallographic, desired geometrical and metallurgical structures. This review paper is aimed to summarize applications of WO3 thin films
as an electrochromic material and the effect of various deposition techniques on its electrochromic and optical properties.
Keywords: Tungsten oxide; Sputtering; Sol-gel; Spray Pyrolysis; Electrochromic, Smart Window
INTRODUCTION
WO3[1], NiO[2], TiO2[3], V2O5[4] which are considered as
inorganic EC material while viologens[5], polyaniline
(PANI)[6],poly(3,4 ethylenedioxythiophene) (PEDOTs)[7] are
common organic and polymer EC materials. Among all inorganic
material WO3 have high coloration efficiency, quick response time
and long life[8].Tungsten was first introduced in the 18th century by
Peter Woulfe who was the first person to recognize this new
element. He introduced this element as wolframite, so tungsten was
originally known as wolfram, explaining the choice of "W" for its
elemental symbol. In year 1841 Robert Oxland gave the first
procedure for preparing tungsten trioxide and he found that tungsten
trioxide (WO3) is a wide band gap metal oxide having good
semiconductor property for various applications including
electrochromic materials and gas sensors[8]. WO3 films also possess
good hydrophilic, gasochromic and photochromic properties. The
first electrochromic study on tungsten trioxide was reported in
1969[9]. The most promising application of this coating is as a
switchable glazing for a smart window, which can save energy for
air conditioning.
Recently, WO3 films have been considered for use as dielectric
layers in multilayer heat mirror coatings on building and automotive
glasses. For most of these applications, thin films of WO3 with
nanometer thickness are usually deposited on glass or polymeric
substrates. A variety of conventional deposition methods have been
used to prepare WO3 films, such as direct current (dc) or radio
frequency (rf) magnetron sputtering[10-18], sol–gel methods[19-
21], plasma spraying method[22], electron beam
evaporation[23,24],thermal evaporation [25,26] and hydrothermal
methods[27].Tungsten oxide has a cubic structure which is also
described by “empty-perovskite” type structure formed by WO3. In
octahedral structure atoms are share at corners[8,10]. The empty
space which is available inside the cube is filled by an interstitial
atom. In interstitial sites the guest ions can be inserted. It is observed
that both an amorphous and crystalline WO3 thin films exhibit
electrochromic coloration property due to ionic insertion. In case of
amorphous WO3, the absorptance modulation during ion and
electron insertion occurs in the visible and near-infrared regions of
the spectrum. In crystalline WO3, however, the injected electrons
are to a significant extent delocalized and behave like free electrons.
The free-electron like behavior results in a reflective optical
modulation which can be described by a modified Drude model. It
is generally believed that the color change in the films is related to
injection and extraction of electrons and metal cations[28].
The general electrochromic phenomenon of WO3 is due to the
formation of tungsten bronze (MxWO3) according to the following
equation:
3
3 WO
M
xe
xM
WO x


 

(Transparent) (Blue)
where M =H, Li etc. At low x the films have an intense blue color
caused by photo affected intervalence charge transfer (CT) between
adjacent W5+ and W6+ sites. At higher value of x, the metallic
“bronze” is formed which is red or golden in color. By cathodic
polarization process ion insertion and electron injection takes place.
The ions which are inserted will expand the lattice of the guest oxide
while the electrons modify its electronic structure and in turn change
its optical properties[9]. In general the electrochromic devices are
classified in two types. In first type, the electrodes used are made of
conducting glass and wrapped by an organic or inorganic polymer
or plastic. This type of configuration was used in electrochromic
windows and is bistable. The main limitation of this type of devices

116 Vyomesh R. Buch et al.
Appl. Sci. Lett. 1(4) 2015, 115-124 www.appslett.com Copyright 2015 Asian Scientific Publishers
REVIEW ARTICLE
is that they show slow color change due to the small amount of
migration rate of the ions in the bulk polymer. Bright color changes
are not possible here. Dissolving two complementary
electrochromic molecules in a solvent is the second type of
electrochromic device. This type is simpler than first type, the dark
and bright color achieved by the reaction of solvent. The main
drawback of this type is that it requires an electrical current to
maintain in the colored state. The colored molecules diffuse through
the system and react to restore the bleached states. This type cannot
be used for large area devices. To overcome these problems an
electrochromic system is needed which is both bistable and changes
color rapidly[29]. When a suitable colorless molecule in oxidized
state and colored molecule in reduced state is attached onto the
surface of a colorless semiconducting electrochromic material
(present case, WO3) on conducting glass Indium-doped tin oxide
(ITO) substrates the above process can be accomplished. When a
negative potential is applied to the conducting glass then it injects
electrons into the conduction band of the semiconducting
electrochromic material and reduces the absorbed molecules. When
a positive potential is applied then the molecules get bleached, due
to this the electrochromic material coloration efficiency of the
molecular systems gets increased. The ultimate interest in the
electrochromic materials is the fabrication of electrochromic device,
which can control the transmittance of the reflectance of the incident
light.
Electrochromism has remained an active area for basic[30] and
applied research with large possibilities for applications in emerging
technologies since many years. Some of the applications are already
developed at the technological level and are commercialized
successfully whereas some are still in the developmental stage. Few
of them are already available in market such as electrochromic
windows, which are used in office windows, architectural and
automobiles, rear-view mirror for car and vehicles, and large area
EC display devices. Some other application like eyewear, visors of
helmets, electrochromic paper will be available in near future.
However, due to lack of manufacturing techniques and durability of
the available devices the ECD are not so common in markets.
APPLICATION & ELECTROCHROMIC PARAMETERS
The principles of these devices are explained briefly in this section
[29]. There are four main applications of electrochromic devices and
are shown in fig. 1(a)-1(d).
1. Information Display: Researchers have been working on
information displays since the discovery of electrochromic device
[31]. The electrochromic display can act in either reflectance or
transmissive modes; the majority of devices work in the reflectance
mode. The EC display can be easily viewed from any angle so it is
particularly useful where people are walking (on railway station,
airport, traffic direction boards, etc). People have also put efforts to
use it in television and digital watch display. Switching time and
high color reproducibility over a large number of switching cycles
are the major shortcomings in using such devices [fig.1(a)].
2. Mirror with variable specular reflectance: The electrochromic
mirrors are (operated in a reflectance mode) one of the important
applications of ECD. Reflecting intensity is reduced as an optically
absorbing color is induced over the reflecting surface[32]. Here total
opacity is to be avoided, to persist a slow reflection in the darkened
state. The self-darkening EC rear-view mirror generally available
for cars and other vehicles is one of its important applications.
During daytime, the rear view mirror is adjusted in such a way that
the electrochromic component is in the bleached state resulting in a
reflection from the back-reflecting part of the mirror. At night, the
mirror is adjusted in such a way that the headlights behind the car
only hit a photosensitive sensor on the front glass surface of the
mirror. Therefore, it resists the light from following vehicles and
thereby improves driver’s comfort. The device needs to be able to
switch at least 104 - 105 cycles without visible degradation, with a
switching time of less than 5s [fig.1(b)].
3. Smart windows: One of the most important applications of ECD,
which are available in market, is the EC window. This
electrochromic window is also known as “Smart Windows” and it
is new technological development which automatically controls the
amount of light and solar energy in buildings and provides comfort
[33,34]. It is also used in architectural glazing or skylights to control
the solar heat entrance and to save energy for air-conditioning in
summer and heating in winter[35,36]. Furthermore, it is also used in
automobiles, airplane, and trains in order to avoid dazzling. Such a
Figure 1. Application of Electrochromic Device [29]

A Review on WO3 films prepared by various methods 117
REVIEW ARTICLE
device needs a high transmittance modulation and lifetime of at least
20 years with switching time of few seconds to few minutes [fig.
1(c)].
4. Variable emittance surfaces: Variable emittance surface device
are special design with a crystalline tungsten oxide film [fig.1(d)].
Intercalation/deintercalation ions make this surface infrared
reflecting or absorbing whose thermal emittance is high [29].The
following are some of the properties required for quantifying the
ECD: high transmittance modulation, high-coloration efficiency,
low-switching time, good-memory effect, and long cyclic life.
1. Transmittance Modulation (ΔT): Transmittance modulation is
one of the most important electrochromic parameter for
electrochromic device operations. It is defined as the transmittance
change in colored and bleached state. Since the transmittance
modulation depends on the wavelength, the change in the
transmittance is measured by the optical transmittance spectra of the
bleached (Tb) and the colored (Tc) state of the sample as a function
of wavelength (λ):
c
b T
T
T 


Generally, ΔT, lying between 70 – 80 %, is particularly used for
device applications [37,42].
2. Coloration Efficiency (CE): Another key parameter for the
electrochromic devices application is the coloration efficiency (CE)
also known as electrochromic efficiency. The CE is described as
how large is the magnitude of optical modulation formed by per
injected/extracted charge i.e., the change in the optical density
(ΔOD) per unit of injected/extracted charge density (Q) per unit
electrode area:
Q
OD
CE


The ΔOD depends on the light absorption ability of electrochromic
materials. The change in the optical density is measured from the
optical transmittance spectra of the bleached (Tb) and the colored
(Tc) state of the sample:
c
b
T
T
OD log


The charge density i.e. the charge injected per unit electrode area of
the film is obtained from integration of the corresponding current
for total time:
A
t
I
Q


where, I is the current (A), t is the total time (s) for which the current
is passed and A is the area of the electrode (cm2). CE is positive if
coloration is generated catholically and negative if coloration is
generated anodically[37,42].
3. Switching Time: Switching time (t) is the time required for the
coloring or bleaching process of an ECD. Coloration time (Tc) is
defined as the time required switching from the bleached state to the
colored state (90 % to 10 %) and the bleaching time (Tb) is the time
taken to switch from the colored state to the bleached state (10 % to
90 %). Some applications do not require a rapid color change such
as the electrochromic office windows, which requires a very slow
response; however, applications such as display devices, require a
more rapid response. The switching time is influenced by certain
factors viz. ionic conductivity of the electrolyte, the applied electric
field, device area, and film structure [37,42].
4. Memory Effect: Depending on the polarity of the applied
voltage, the ECD can exist either in colored or bleached state, which
will be retained by the ECD after removal of the voltage; this effect
is called “open-circuit memory effect.” This is one of the excellent
benefits of electrochromic devices. In open-circuit condition, when
the inserted charge is self-removed from the electrochromic film,
due to an electrical leakage current or ion diffusion it loses memory,
this phenomenon is called self-bleaching. Therefore, the ion
conductor plays crucial role for the optical memory effect. The
electrochromic memory can be for several days or weeks even
without any current. However, some EC devices may require small
refreshing charges to maintain the charged state because side
reactions or short circuits may change the desired color[37,42].
5. Cycle-Life: It represents the number of color-bleach cycles that
can be performed by the ECD before any significant extent of
degradation has occurred. The cycle-life is therefore a measure of
the electrochromic durability testing. The maximizing of the cycle
life is an obvious aim of device fabrication and a minimum 10,000
cycles are acceptable. ECD are generally used in window and
display applications, deterioration is best gauged by eye vision, and
the same illumination that would be employed for normal device
operation. However, 50% degradation is often tolerable for display
application. The three common reasons for the low cycle life or
device failures are: The TCO layer failure, electrolyte failure, or one
or both of electrochromic layers failure. Most common cause of
TCO degradation is decomposition of TCO, which increases the
resistance and decreases the transparency. The reason for electrolyte
failure is due to solar irradiation and generation of hydrogen gas,
when electrolytes use proton for conduction. In electrochromic
layers failure, the layers gets dissolved when they come in contact
with electrolyte and in other cases, layer changes volume during
redox process[37,42].
6. Cyclic Voltammetry : In cyclic voltammetry a voltage is applied
between tungsten oxide film and a counter electrode. The voltage
was swept back and forth between two set points, usually triangular
manner. The current flowing from film in and out. Cyclic
voltammetry can be used non-quantitatively to give a "fingerprint"
of the electrochemical processes, to trace reversible and irreversible
effects, and to ascertain voltage levels that yield stable operation
[109].
7. Raman Spectroscopy: Raman Spectroscopy gives the information
on tungsten-oxygen bonding. [109]
THIN FILM PRPEPRATION METHODS
1. Sputtering Method
By the bombardment of a target material with accelerated ions, the
evaporation of target material and its deposition on a substrate thin
film formation is carried out. If a reactive species like oxygen or
methane is present in the gas phase then the chemical reaction with
the evaporated target material can occur, leading to the deposition
of a chemical compound. In the past, reactive sputter deposition
processes were widely used for the preparation of oxides, carbides,
nitrides, silicides or oxy-nitrides. The surface and volume
microstructure of the deposited compounds depend strongly on the
preparation procedure. For industrial thin film preparation
sputtering deposition is well known technique. The oxide film
deposited by sputtering method can’t show the same composition
and microstructures as the films made by evaporation technique.
Tungsten oxide films were deposited by reactive DC magnetron
sputtering on various substrates such as quartz, Cr coated glass and
transparent conducting glass and were used for transmittance, raman
scattering and electrochemical measurements [38].WO3 films were
prepared by DC and RF sputtering by Kaneko et al. and Akram et
al. respectively. Beyond certain amount of O2 content, the rate of

REVIEW ARTICLE
deposition goes down and approached a constant value of 0.1 nm/s,
this reduction in oxidation is due to sputtering target. By analysis of
the sputter discharge parameters for tungsten oxide preparation it is
found that when the sputtering rate is higher than it increases the
powder density of the target[39]. Hichwa et al.[40] obtained the
highest rate of deposition around 3.4 nm/s using reactive magnetron
sputtering. By selecting proper sputtering parameters, one can avoid
stress build up during deposition of films and increase the porosity
by oblique angle sputtering [41].Tungsten oxide thin films were
deposited by RF sputtering from a WO3 target (diameter: 12 cm).
The sputtering atmosphere was an Ar-10% oxygen mixture at a total
gas pressure of 5 mtorr. The RF power was 200W operated at 13.56
MHz. Ultrasonically cleaned alumina and glass slides, over coated
with a 5nm layer of amorphous carbon was used as substrates. The
substrates were mounted on a holder and maintained at a constant
temperature of 300˚C and the target was pre sputtered for 30
min[43]. Polycrystalline sample of WO3 was prepared by RF
sputtering on to a substrate held at 325 ± 10°C in an atmosphere of
10% oxygen and 90% argon at 40mtorr. The characterization of the
structure was done by XRD measurements. A bath of 1N H2SO4
with 10% glycerol (by volume) was used as the ion source electron
insulator for coloration and bleaching of the WO3 layer. The results
of the spectroscopic ellipsomsetry measurements of the optical
constants for the polycrystalline WO3 (in various status of
coloration) are independent of reflectivity measurements [44].
Xilian Sun et.al [45] had reported effect of density on
electrochromic tungsten oxide films deposited by dc pulsed
magnetron sputtering with varying working pressure. The target
was sputtered for 10 min before deposition started keeping dc power
100W and pulsed frequency 20 kHz for 5µs. The gas pressure ratio
of Ar/O2 maintain 4 and the total pressure varied from 0.41 to 1.7
Pa. For EC properties were characterized using cyclic voltammetry
method between -1 and +1 V at a scan rate of 20 mV/s in 1.0 M
LiClO4 propylene carbonate electrolyte. It is found that the optical
modulation and coloration efficiency of films are strongly affected
by the amount of tungsten oxide present in the film. The film at
higher working pressure was rough and lower density, which offered
fast EC response. The result shows that as pressure increases the
transmission modulation decreased. Furthermore, the
electrochromic properties of tungsten oxide are strongly correlated
with film density as well as thickness. The optical modulation and
coloration efficiency higher for 0.4Pa total pressure approximately
48% and 32cm2/C respectively. Chin-Guo Kuo et.al [46] reported
Electrochromic properties of Tungsten oxide films deposited by DC
Magnetron sputtering. The films were deposited for 2 hrs. keeping
temperature 400˚C and then it were eletro-polished at constant 60V
using H2SO4 and methanol at 20˚C and then DC voltage were
applied keeping temperature is constant 25 ˚C, then it was anodized
in NaF solution. Then it was observed that 20V, 40 V samples were
observed nanotubular layer but at 100V it was observed the sample
had mesh-like porous structure. It filled by various electrolyte filled
volume 10 mm3,30 mm3,50 mm3,70 mm3,100 mm3 and it was found
that transmittance in descending order 100
mm3>70mm3>50mm3>30mm3>10mm3 and the could reach
maximum coloration efficiency 15.2 cm2
/C. Ya-Chi Chen et.al [47]
reported Electrochromic Properties of Tungsten-Titanium Oxide
Films deposited by pulsed magnetron sputtering. The films were
deposited at different plasma powers 100, 200, 300, 400 and 500 W
using a gaseous Ar (150 sccm)/O2(50 sccm) mixture at fixed
working pressure 5 × 10-2 torr. Electrochromic properties were
improve with deposition power caused by the doping with Ti. The
400 W. WTiOx film is the best for electrochromic applications. The
transmittance (ΔT, %) of the 400 WTiOx film between the bleached
and colored states at 400 nm is 25.8%, at 550 nm is 52.5% and at
800 nm is 62.4%. Jow-Lay Huang et.al [48] has reported
electrochromic properties of tungsten oxide films deposited by
electrochemical anodized RF-sputtered. Tungsten oxide films of
various morphology, crystallinity, and porosity can be prepared by
carefully altering the anodization time (20–50 min) and annealing
temperature (450–550 °C). Porosity influences the diffusion of Li+
ions within the electrochromic material and thus affects the
electrochromic property. The pore structure of the 500 °C annealed
WO3 film exhibits the optimal pore network for the diffusion of Li+
ions and possesses the superior EC property. Thus the EC results
said that film deposited after 40 min anodization and 500˚C
annealed temperature had good modulation of 43.6% and coloration
efficiency of 42.8 cm2/C. S.S. Kalagi et al [49] has reported that the
tungsten oxide films deposited by varying the sputtering time using
RF sputtering. The working pressure was maintained 1x10-2 torr.
Oxygen content maintain 40% by keeping applied power to target
constant 140W and substrate temperature 23.2˚C constant. The
sputtering time varies from 30, 45, 60 min. It was observed that the
film deposited at 30,45,60 min sputtering time shows transmittance
modulation 18%,32% and 55% respectively. The result shows that
60min sputtering time shows higher transmittance modulation 55%.
The device shows a coloration efficiency (C.E.) of 46.45 cm2 C−1
and reversibility of 98%.
2. Sol-gel Method
Dipping, spin-coating or spraying is the method used for thin film
preparation using sol-gel method. Using poly-condensation process
the first colloidal oxide is produced either by acidification process
and organo-metallic compound is formed [50]. Chemseddine et
al.[57-61] and Habib et al.[62-66] used the sol-gel technique which
has been surveyed [51-56] as the most widely studied technique.
The acidification process done by pursing a solution based on
sodium tungstate or potassium tungstate through a proton exchange
resin. In this method solution was applied to glass plate, either
directly as drop or by spin coating and spraying, after drying or by
heating the hard coating with good electrochromic and optical
properties obtained. W-PTA sols were prepared in 18 ml of (30%)
H2SO4 which reacted with small percentage of metallic powder
[5gm, 91%]. The mixture was stirred for 12 hours at room
temperature until tungsten powder was dissolved. Platinum net was
then added to the mixture to remove any unreacted H2O2. The sols
with a deep brown color were stored at -25°C to prevent gellation
prior to dipping. This gellation process can be reversed by adding
small amount of H2O2 until the dark brown sol is reformed [67].
Films were obtained by heat treatment and their thickness were in
the range of 150 nm/dipping up to 5 dipping thereby yielding
600nm thick films [68]. Dip coating is the method in which a
solution of tungsten hexaethoxide or tungsten oxo-tetra has been
applied successfully by Bell et al.[68]. They dipped substrate at
5nm/s speed and DTA/TGA analysis shows result of WO3 gel gets
crystalline phase and by performing electrochemical
characterization method, WO3 film coated on ITO glass than
coloration was done by adding H+ ion. The thickness of WO3 film
was found around 1250Å. P. S.Patil et. al [69] had reported sol-gel
method for synthesis and chemically grown electrochromic tungsten
oxide. They were used FTO coated glass substrate and washed with
labolline solution and then double distilled water then after it was
dipped in chromic acid for 20 min and rinsed with double distilled
water. Then substrates were etched in 0.1 M H2SO4 in order to
improve adhesion. Substrates were cleaned with double distilled
water and dried in alcoholic vapour. It was seen that at the terminal
growth of film, the film thickness remains constant after 15 min at

REVIEW ARTICLE
640 nm wavelength and there was no further increase in thickness
observed. For electrochromic property measurement using three
electrode cell configuration with 0.5 M LiClO4 /propylene carbonate
as the electrolyte, platinum as the counter-electrode, tungsten oxide
as the working electrode and the saturated calomel electrode (SCE)
as the reference electrode and -0.8 to +0.8 V potential applied with
100mV/s scan rate. The result shows maximum coloration
efficiency 12.57 cm2/C at 630nm.In same year Wang W. et al [70]
had reported sol-gel method for mesostructured tungsten oxide films
for electrochromic properties. They were used tungstic acid, H2O2
35%wt.water solution and the non-ionic surfactants Brij56
(C16EO10, C16H33 (OCH2CH2)n OH, n=10), Tween 60 (C24H46O6
(C2H4O)n, n=20). Peroxotungstic acid (PTA) was prepared by the
reaction between H2WO4 with hydrogen peroxide. The PTA and
surfactant in mixed solvents of water and ethanol, with weight ratio
PTA : Surfactant:H2O:ethanol of 1:0.2:4.5:2.25. The sol prepared
was used for dip coating on glass substrate. The deposited film was
allowed to dry at room temperature and then, was further thermally
treated at temperatures at 100–450˚ C for between 1 and 20 h to
solidify the film and remove the template. For electrochemical
properties three electrode configuration method was used in which
the working electrode consisted of the dip coated TOFs deposited
on ITO coated glass in 0.1 M aqueous solution of sulphuric acid.
An Ag electrode (Ag/AgCl/saturated KCl) and a platinum needle
were taken as the reference and counter electrode, the result shows
that the coloration efficiency 44cm2/C and higher charge density up
to 8.2 mC/cm2 at 100nm.
Y. Djaoued et.al [71] has used sol-gel method for deposition of
tungsten oxide film. They were used an acylation reaction between
poly (propylene glycol), bis (2-aminopropyl ether) (2-APPG) with
isocyanatopropyltriethoxysil- ane (ICS) in tetrahydrofuran (THF) in
the volume ratio 1: 0.1: 1. They were observed structure at various
temperature 400,500,600C they found grain size 10,19,25nm. They
were also found that the transmission in bleached state 76.4% at
1100nm wavelength, when the coloration potential applied 2.5V and
bleach voltage applied -1.0V. P. N. Bhosale et.al [72] has reported
sol-gel method for study of Ag nanoparticle in decorated tungsten
oxide films and then study the electrochromic properties. They were
used AR grade sodium tungstate dihydrate, Na2WO4. 2H2O, 3 M
Hydrochloric acid, HCl, oxalic acid, (C2H2O4·2H2O), potassium
sulphate (K2SO4), polyethylene glycol (PEG), polyethyl glycol-p-
iso octyl phenyl ether (C34H62O11) i.e. Triton X-100, high purity
silver powder (99.5%) and double distilled water. They were heat
the sol at different annealing temperature ranges from 300-500K for
different film thickness 15nm, 20nm, 25nm. As a result they were
found that the higher coloration efficiency 118.02 cm2/C for 25nm
thickness.
3. Spray- pyrolysis Method
Hurditch used spray aqueous solutions of metatungstic acid
(H6W12O39) [73]. Spray deposition, using solutions of WCl6
dissolved in ethanol or NN-dimethyl formamide, was carried out
[74] where spraying took place in air on to substrates heated up to
500˚C. The tungsten oxide films thus formed showed
electrochromic property. XRD spectra gave evidence of some
chlorine contamination in the film. XRD showed that films
deposited at temperatures more than 300°C were crystalline.
Sivakumar et al.[75] have deposited monoclinic WO3 films at
250°C and at higher wavelength region observed the optical studies
may be due to coloration effect on thin films. P. Schmuki et.al [76]
had prepared thick porous tungsten oxide films by anodization of
tungsten in fluoride containing phosphoric acid electrolyte. They
were prepared electrolyte by adding 35.4 ml concentrated HF into
64.6 ml concentrated H3PO4 finally to an 8 M HF concentration. The
films were anodized for different time period 10min, 20min, 40min,
60min, 120min by applying circuit potential of 40V with sweep rate
of 300mV/s. To analyses electrochromic properties of tungsten
oxide film the film characterized in an aqueous solution of 0.1M
HClO4. The results shows that the film deposited at 2µm thickness
was gave higher value of coloration efficiency 54.95cm2/C.
R. S. Patil et.al [77] has reported electrodeposited method for
tungsten oxide for electrochromic property. They were prepared
tungsten electrolyte by dissolution of 3.74g tungsten powder in 40
ml H2O2 (30%). Then exothermic reaction conducted at 0˚C and
10˚C. Mixing this solution with anhydrous absolute ethanol and
water in the ratio of 2:3 yielded the deep yellow-colored deposition
sol, which was refluxed at 55˚C for 1 h to decompose off excess
peroxide. Then graphite was used as counter electrode and SCE
used as reference electrode, then constant potential supplied for 15
min at room temperature. For measurement of electrochromic
property they were take film in to 0.5M LiClO4-PC electrolyte at
different scan rates with a potential window from +1.4 to -1.4V
versus SCE. They observed the transmission modulation and
coloration efficiency at 630nm wavelength 74% and 92cm2/C
respectively. A. Duta et.al [78] had prepared tungsten oxide film for
synthesis of electrochromic properties using pyrolysis method of
deposition. They were prepare precursor solution by dissolving 2.2
g of WCl6 powder) in ethanol which contain acetyl acetone with
WCl6 and acetyl acetone in a 1:2 M ratio. Hexadecyl- trimethyl-
ammonium bromide (HTAB) and polyethylene glycol (PEG 400)
were added in the spraying solution in different amounts. The film
deposited at 0 ppm, 200ppm, 500ppm of HTAB and PEG400. The
result obtained shows that the film deposited at 550nm shows
Figure 2. (a) WO3 film thickness after different anodization time in
a concentrated H3PO4 and 8 M HF electrolyte under the anodization
potential of 40 V. The insets show the thicknesses of resulting films.
(b–f) SEM top-views of the WO3 films fabricated [76].

REVIEW ARTICLE
different transmission modulation 23%, 27%,38% and coloration
efficiency 18.4cm2/C, 19cm2/C, 31.5cm2/C respectively. So they
were found that the film deposited at 500ppm shows higher
transmission modulation and coloration efficiency. C. Henrist et.al
[79] had reported electrochromic properties of tungsten oxide film
by spray pyrolysis for improved coloration contrast. They were used
ammonium metatungstate and polyethylene glycol as a precursor.
They were observed coloring and bleaching tungsten oxide film by
inversion and extraction of lithium based electrolyte and they were
found first coloration occurs as -1.74V potential for 3 min. and
bleached at +1.06V for 3 min. The transmission modulation of 83%
and coloration efficiency 28.0 cm2/C at 550 nm.
G. Leftheriotis et.al [80] had reported fabrication method of
tungsten oxide film by spray pyrolysis. They were used 0.36gms of
tungsten oxide powder and 20mL of 15% H2O2 to prepared
precursor. This solution was heated at 80˚C for half an hour.
Precursor solution was used for growth of tungsten oxide film. For
deposition the K glass was used as substrate. For measurement of
electrochromic properties 1 M lithium perchlorate dissolved in
propylene carbonate (LiClO4-PC) used and 2 to 31 mC/cm2 charge
was supplied. Then they were found to be 132 cm2/C at 389 nm,
48.9 cm2/C at 534 nm and 52.4 cm2/C at 800 nm.
4. Electron beam evaporation Method
Condensation of the vapour produced by sublimation from hot
tungsten powder is the standard technique for making tungsten
oxide film for laboratory study [59]. In this method heating can be
done by a resistive boat (Ta, Mo and W) or by a reaction crucible or
by an electron beam, sometime water free powder is also used as
substrate for deposition and the substrate temperature kept up to a
few hundred degrees in unheated condition. The evaporation takes
place due to non-reactive gases. By this evaporation technique good
electrochromism thin films are made. The deposition rate gets
increased by placing the substrate nearer to the vapour source. The
vapour produced during this method of heating does not contain any
individual atoms but it contains molecular nature. The dominating
species is trimetric W3O9 molecules, dependent on experimental
conditions [81]. The deposition rate was 4-5 (Å/s), the deposition
angle was varied within 40˚ with a planetary rotation, and the
substrate temperature was usually maintained at 80°C after keeping
at 1l0°for 5 min. The total gas pressure in the chamber during the
evaporation process was controlled by introducing N2 gas and
maintained around 5.0-6.5 x 10-2 Pa [81]. Deposited WO3 films were
analyzed by X-ray diffraction and found to be amorphous. The
packing density of the film, calculated from the film thickness and
weight, was 38 g/cm3 [82]. Sivakumar et al.[83] have studied the
optoelectronic properties of WO3 films electron beam evaporated at
different substrate temperatures and study shows that it transformed
from amorphous to crystalline nature by increasing the temperature
and from optical study it is found that they have good coloration
effect and stoichiometric nature. Table 1 shows reviews observed
for electrochromic and optical properties using various deposition
methods which show at the end of the paper. Development of
semiconducting oxide materials with controllable energy gap is
necessary for the increased applications in electrochromic liquid
crystal display and optoelectronic devices. Hence the absorption and
transmission properties were studied in detail to calculate the band
gap variations and the related optical properties. For heavily
disordered evaporated WO3 films band gap varied from 3.2 to 3.4eV
[97]. The band gap depends on the materials preparation conditions
and the temperature of evaporation. Miyake et al. [98] reported a
monotonic drop of Eg with increasing temperature. The band gap
Table 1: Electrochromic Properties of WO3 Films.
Research Group/ Year Deposition Technique Variable Parameters Electrochromic Ref.
K. Lee et al.(2013) RF Sputtering Power 100, 200, 300,
400 and 500 W
CE = 30.2 cm2/c 84
J.Chen et al. (2012) Spray Pyrolysis Voltage
20,40,60,80,100V
CE =15.2cm2/C 85
K. Weng et al. (2012) pulsed magnetron sputtering Power 100, 200, 300,
400 and 500 W
OD= 0.85 86
J.T. Chang et al. (2012) Reactive DC magnetron sputtering O2/Ar ratio,
Current(0.3,0.5,1,1.5A)
Not studied 87
M.Rao. et al. (2011) Evaporation evaporation temp range
303-603K
contrast 88
H. Kawasaki et al. (2009) RF magnetron sputtering O2:Ar = 5:5,6:4,7:3, 8:2,
9:1
Relative density:
0.78,0.85,0.92
89
A. Rougier et al. (2008) RF Sputtering Temp. RT to 400˚C Absorption
coefficient : 0.1
90
K. Muthu Karuppasamy (2008) DC magnetron sputtering Voltage 450,490,530V Not studied 91
J. Augustynski et al. (2006) Sol-gel Method Temp. 250-550˚C CE =40cm2/C 92
B. Almeida et al. (2002) Reactive DC magnetron sputtering Temp. RT to 200˚C , O2
pressure = 0.2-0.8
Not studied 93
M. Hepel et al. (2000) Electrochemically Potential different +0.5
to -0.5V
CE max=59.9 cm2/C
at -0.350V
94
P.S. Patil et al. (2000) Solution thermolysis scan rate
10,20,50,100,200 mv/s
CE= 25cm2/C @
633nm
95
A. Pennisi et al.(1992) Electrochemically No of Cycle -
60,100,150,200
Not studied 96

REVIEW ARTICLE
was changed from 3.25 to 2.7eV. The decrease is strongest at
temperature >300˚C which indicates that crystallization is cawing
the band gap narrowing for sputter deposition, the band gaps have
been reported 3.0 <Es<3.4 eV [97, 99]. For sputter deposition the
authors reported 3.0 to 3.4 eV with a tendency that a high pressure
of the sputter gas and high O2 mixture in reactive sputtering. This
process gave a low Eg[100]. Crystallized films produced by
sputtering shows band gap of 2.9 eV [101] and by chemical vapour
deposition showed a band gap of 3.2 eV [102]. A thickness
dependent change in the crystalline or tungsten oxide films made by
anodizing is observed with the band gap values of 3.05 and 3.73 eV
[103]. Crystalline anodic films with monoclinic triclinic, and
orthorhombic structure and different degrees of hydration had the
band gap of 2.55<Es<2.79eV as observed by the photo electro-
chemical measurements [104]. Kubo and Nishikitani [105] reported
that the optical band gap converges to a constant value between 2.8
and 2.7eV that was assigned to crystalline WO3 film. The hydrogen
tungsten bronze is a reasonable semiconductor at low values of x
(x=0.3 to 0.5) of HxWO3 [106]. Rottkay et al.[107] recorded the
optical measurements with a variable angle spectroscopic
ellipsometer from 280 to 1700nm. Upon coloration the agreement
between effective medium theory and optical measurements
deteriorates. The injected electrons are trapped at the energetically
lower sites, thus giving the compound character of a preferred
component, possibly the one with smaller atomic number. Films
prepared in the sol-gel process showed good transmission
modulation at wavelengths higher than 520nm, more that 50% and
at lower wavelength the transmittance was very less [108]. All
transmittance and reflectance spectra showed the typical
interference structure caused by both ITO and WO3 layers. As the
injection charge of WO3 increases the absorbance also get increased
and due that the WO3 will gets converted in tungsten bronze having
blue color. The incomplete oxidation of evaporated tungsten oxide
does not lead to the expected optical absorbance [109]. Azens et
al.[110] reported that the transmittance for as-deposited film
increases strongly as one goes towards longer wavelengths in the
luminous range. This feature was not typical for electrochromic
tungsten oxide films. At the same time the luminous transmittance
of unpolarized light is 46% at +60° and 35% at -60˚ in the as-
deposited state whereas the corresponding numbers are 15% and 9%
in the colored state. This clearly manifested that angular selectivity
may be of interest for applications of electrochromic smart
windows, inclined windows. The reflectance spectra of WO3 films
showed significant reflectance variation in the infrared region which
coincides to sputter deposited WO3 films [111]. Golden and Steele
[112] reported that in the normal transmission mode, the
electrochemically lithiated WO3 films showed brown coloration on
high levels of lithiation. The transmission spectra for x=0.3 and 0.5
show a very broad peak in the near IR regions. Bader et al.[113]
reported a theoretical outline for the reflection and transmission
spectra obtained from spectroscopic ellipsometer technique on thin
films deposited on a thick transparent substrate. The optical
parameters are shown as a function of the wavelength for the as
deposited WO3 films before insertion of lithium. The observed
optical variation in the tungsten trioxide films are comparable to the
reported results for the tungsten trioxide films prepared by
electrochemical and thermal evaporation techniques. In the
potassium ion intercalation process, the transmission spectra of the
WO3 film deposited on TCO exhibits an extremely high degree of
transmission (80%) in the as-deposited state [114].
CONCLUSION & DISCUSSION
Devices based on electrochromism with their tunable transmission
for visible and infrared radiation will play an important role for
architectural and automotive glazing. As WO3 is
thermodynamically stable at room temperature, it is considered as
the most suitable material for the electrochromically active
electrodes in the electrochromic devices. In this review paper the
various methods used for deposition such as sputtering, sol-gel,
spray pyrolysis, electron beam evaporation are studied and it is
found that out of all these technique sputtering is most widely used
for deposition. The materials properties, preparation techniques,
colorations/bleaching efficiency and the electrochromic devices
developed are elaborately presented in this review.
*Corrsponding author: vyomdhar_19@yahoo.co.in
Tel. +91-9427450020
REFERENCES
[1]. Yung-Eun Sung et.al, Fast switchable electrochromic
properties of tungsten oxide nanowire bundles. Applied
Physics Letters, 90, 173126 (2007).
[2]. Mao-Sung Wu et.al, Electrochromic properties of
intercrossing nickel oxide nanoflakes synthesized by
electrochemically anodic deposition. Applied Physics Letters,
91, 033109 (2007).
[3]. Patrik Schmuki et.al, High-contrast electrochromic switching
using transparent lift-off layers of self organized TiO2
nanotubes. Small, 4, 1063-1066 (2008).
[4]. Keng-Che Cheng et.al, V2O5 nanowires as a functional material
for electrochromic device. Solar Energy Materials and Solar
Cells, 90, 1156-1165 (2006).
[5]. Donald Fitzmaurice et.al, Electrochromic windows based on
viologen-modified nanostructured TiO2 films. Solar Energy
Materials and Solar Cells, 55, 215-223(1998).
[6]. N. Gospodinova et.al, Conducting polymers prepared by
oxidative polymerization: polyaniline. Program Polymer
Science, 23, 1443-1484 (1998).
[7]. Magnus Berggren et.al, Printable all-organic electrochromic
active-matrix displays. Advanced Functional Materials, 17,
3074-3082 (2007).
[8]. M. C. Rao, Structure and properties of WO3 thin films for
electrochromic device application, Journal of Non- oxide
Glasses, 5(1),1-8, (2013).
[9]. Prakash R. Somani et.al, Electrochromic materials and
devices: present and future. Materials chemistry and physics,
77,117-133, (2002).
[10]. Horng-Hwa Lu, Effects of oxygen contents on the
electrochromic properties of tungsten oxide films prepared by
reactive magnetron sputtering. Journal of Alloys Compounds,
465, 429–435(2008).
[11]. Valyukh et.al, Spectroscopic ellipsometry characterization of
electrochromic tungsten oxide and nickel oxide thin films
made by sputter deposition. Solar Energy Materials and Solar
Cells, 94, 724–732 (2010).
[12]. C. Sant et.al, Morphological and mechanical properties study
of [WO3/W]n nanoscale multilayers. Thin Solid Films, 479,
201–206,(2005).
[13]. A. Cavaleiro et.al, Tungsten oxide with different oxygen
contents: Sliding properties. Vacuum, 81, 1426–1429(2007).
[14]. N.M.G. Parreira et.al, Synthesis, structural and mechanical
characterization of sputtered tungsten oxide coatings. Thin
Solid Films, 510, 191–196, (2006).

REVIEW ARTICLE
[15]. T. Polcar et.al, Structure, mechanical properties and tribology
of W–N and W–O coatings. International Journal Refractory
Metals and Hard Materials, 28, 15–22, (2010).
[16]. A. Gorenstein et.al, Influence of the microstructure on the
electrochemical performance of thin film WO3 cathode.
Journal Power Sources, 162, 1351–1356 (2006).
[17]. AA Akl et.al, Characterization of tungsten oxide films of
different crystallinity prepared by RF sputtering. Physica B:
Condensed Matter, 325B, 65–75 (2003).
[18]. Huiyao Wang et.al, The preparation and properties study of
photocatalytic nanocrystalline/nanoporous WO3 thin films.
Materials Design, 23, 331–336 (2002).
[19]. Xilian Sun et.al, Influence of annealing temperature on
microstructure and optical properties of sol–gel derived
tungsten oxide films. Applied Surface Science, 255, 8629–
8633 (2009).
[20]. Caner Durucan et.al, Structural, electrochemical and optical
comparisons of tungsten oxide coatings derived from tungsten
powder-based sols. Thin Solid Films, 518, 104– 111 (2009).
[21]. Balaji S et.al Porous orthorhombic tungsten oxide thin films:
synthesis, characterization, and application in electrochromic
and photochromic devices. Journal of Material Chemistry, 21,
3940–3948 (2011).
[22]. Chao Zhang et.al, Sensing properties of atmospheric plasma-
sprayed WO3 coating for sub-ppm NO2 detection. Sensor and
ActuatorsB :Chemical, 144, 280–288 (2010).
[23]. Coloration and bleaching mechanism of tungsten oxide thin
films in different electrolytes. Surface Engineering, 23 (5),
373– 379 (2007).
[24]. R.J. Lad et.al, The influence of microstructure on tribological
properties of WO3 thin films. Wear, 232, 84–90 (1999).
[25]. M.F. Al-Kuhaili et.al, Transparent heat mirrors based on
tungsten oxide–silver multilayer structures. Solar Energy, 83,
1571–1577 (2009).
[26]. A. Cavaleiro et.al, Tungsten oxide with different oxygen
contents: Sliding properties. Vacuum, 81, 1426–1429 (2007).
[27]. J.P. Tu et.al, Electrochromic behavior of WO3 nanotree films
prepared by hydrothermal oxidation. Solar Energy Materials
and Solar Cells, 95, 2107–2112 (2011).
[28]. J. S. E. M. Svensson et.al, Electrochromic coatings for smart
windows: Crystalline and amorphous WO3 films” Thin Solid
Films 126, 31 (1985).
[29]. M. Jayachandran et.al, Review on WO3 Thin Films: Materials
Properties, Preparation Techniques and Electrochromic
Devices, Transactions of the SAEST , 40,42-61 (2005).
[30]. W.K. Zhang et.al, Electrochromic properties of porous NiO
thin film as a counter electrode for NiO/WO3 complementary
electrochromic window. Electrochimica Acta, 56(11) 4281-
4286 (2011).
[31]. K. Tajima et.al, All-solid-state switchable mirror on flexible
sheet” Surface Coating Technology, 202(22-23) 5633-5636
(2008).
[32]. M.Green, Electrochromic displays Displays, 9 ,166-200
(1988).
[33]. J. S. E. M. Svensson et.al, Electrochromic tungsten oxide
films for energy efficient windows. Solar Energy Materials,
11 , 29-34 (1984).
[34]. E.S. Lee et.al, End user impacts of automated electrochromic
windows in a pilot retrofit application. Energy and Buildings,
47 , 267-284 (2012).
[35]. C G Granqvist, Smart windows and intelligent glass façades.
Smart Materials Bulletin, 10, 9-10 (2002).
[36]. A. Azens et.al, Electrochromic devices on polyester foil.
Solid States Ionics,165(1-4),1-5 (2003).
[37]. M. Scholten et.al, On the Mechanism of ITO Etching: The
Specificity of Halogen Acids. Journal of Electrochemical
Society, 140(2), 471-475 (1993).
[38]. M.L.Perry et.al, Mass Transport in Gas‐Diffusion Electrodes:
A Diagnostic Tool for Fuel‐Cell Cathodes. Japan Journal
Electrochemical Society, 145(1) , 5-15 (1998).
[39]. D. Green, Properties of Tungsten oxide and trigonally bonded
compounds. Ph.D thesis, University of Sydney, Australia
(1991).
[40]. B. P. Hichwa et.al, Electrical and optical properties of thin
Ta and W oxide films produced by reactive direct current
magnetron sputtering. Journal Vacuum Science Technology,
A 5 , 1775(1987).
[41]. K. Kaneda et.al, Physical properties of tungsten oxide films
deposited by a reactive sputtering method. Japan Society of
Applied Physics, 30(1), 1841-1846(1991).
[42]. K.J.Patel, Studies on electrochromic thin film devices and
sensors” PhD Thesis, (2013).
[43]. Akram H et.al, Electrochromic properties of rf‐sputtered
tungstic oxide film prepared from a W metal target.” Journal
of Applied Physics., 66(9) , 4367-4367(1989).
[44]. L. Alexander et.al, Vapour density and vibrational spectra of
MoOF4 and WOF4. The structure of crystalline WOF4.
Journal of the Chemical Society Daltoon Trans., 81-84(1974).
[45]. Xilian Sun et.al, Effects of film density on electrochromic
tungsten oxide thin films deposited by reactive dc-pulsed
magnetron sputtering, Journal of Alloys and Compounds
504S , S418–S421(2010).
[46]. Chin-Guo Kuo et.al, Experimental Study of the
Electrochromic properties of WO3 thin films derived by
electrochemical method , Journal of Marine Science and
Technology, Vol. 20, No. 4, pp. 365-368 (2012).
[47]. Ya-Chi Chen et.al, Electrochromic Properties of Tungsten-
Titanium Oxide Films Journal of Nanoscience and
Nanotechnology Vol. 12, 1–5, (2012).
[48]. Jow-Lay Huang et.al, Characterization of electrochromic
tungsten oxide film from electrochemical anodized RF-
sputtered tungsten films, Ceramics International, 1-25(2012).
[49]. S.S. Kalagi et.al , Transmission attenuation and chromic
contrast characterization of R.F. sputtered WO3 thin films
for electrochromic device applications, Electrochimica Acta
85, 501– 508 (2012).
[50]. B. Munro et.al, Characterization of ElectrochromicWO3-
Layers Prepared by Sol-Gel Nanotechnology. Journal of Sol-
Gel Science and Technology, 13, 673–678(1998).
[51]. C.J. Brinker, et.al Fundamentals of sol-gel dip coating. Thin
Solid Films, 201(1),97-108 (1991).
[52]. C.J. Brinker, et.al Sol-gel thin film formation. Journal of
Non-Crystalline Solids, 121(1-3) , 294-302 (1990).
[53]. C.J. Brinker, et.al, Review of sol-gel thin film formation.
Journal of Non-Crystalline Solids, 147-148 ,424-436(1992).
[54]. C. Brinter et.al, The physics and chemistry of sol-gel
processing. Sol-Gel Science , Academic, Sandiego, 2pp
(1990).
[55]. K.Hara et.al, Optical Characterization of Tungstic Acid
around Gelation Time. Journal of Physics Society Japan, 61
, 2147-2153 (1992).
[56]. J. Livage et.al, Sol-gel Chemistry of Transition Metal Oxides.
Progress in Solid State Chemistry,18(4), 259-341(1988).

REVIEW ARTICLE
[57]. A. Chemseddine Sol-gel processing of an entirely new family
of mixed valence glasses. Journal of Non-Crystalline Solids,
147-148, 313-319 (1992).
[58]. A. Chemseddine et.al, Anisotropic WO3·nH2O layers
deposited from gels. Journal of Non-Crystalline Solids, ,
91(2), 271-278 (1987).
[59]. A. Chemseddine et.al, Handbook of Inorganic :
Electrochromic Materials. RexChim. Minerale, 21,
487(1984).
[60]. C.G. Granqvist et.al, Electrochromism of colloidal tungsten
oxide. Solid state Ionics, 9-10 , 357 (1983).
[61]. R. Morineau et.al, Handbook of inorganic : Electrochromic
Materials. Vide Couches Minces., 222 , 239pp (1984).
[62]. M. Habib et.al, Some Aspects Of Electrochromism of WO3
films Prepared By A Chemical Deposition Method Pmc. Soc.
Photo-Opt, Instrumentation. Energy, 1149, 46(1989).
[63]. D. Glueck et.al, The electrochromic properties of chemically
deposited tungsten oxide films. Solar Energy Materials, 18(3-
4), 127-141 (1989).
[64]. P. Judeinstein et.al, Role of the water content on the
electrochromic properties of WO3, nH2O thin films. Material
Science Energy., B , 3(1-2), 129-132 (1989).
[65]. P. Judeinstein et.al, Electrochromic properties of sol-gel
derived WO3 coatings. Proceedings of the SPIE, 1328, 344-
351 (1990).
[66]. T. Minami et.al, Heat treatment in hydrogen gas and plasma
for transparent conducting oxide films such as ZnO, SnO2 and
indium tin oxide. Thin Solid Films, 176(2),277-282 (1989).
[67]. T. Nanba et.al, Structural study of amorphous WO3 thin films
prepared by the ion exchange method. Journal of Material
Research, 6(6) ,1324-1333(1991).
[68]. Kil Dong Lee et.al, Preparation and electrochromic properties
of WO3 coating deposited by the sol–gel method. Solar
Energy Materials and Solar Cells, 57(1), 21-30(1999).
[69]. P.S.Patil et.al , Thickness-dependent electrochromic
properties of solution thermolyzed tungsten oxide thin films
Solar Energy Materials & Solar Cells 60 ,143-153(2000).
[70]. Wang W. et al, Synthesis and electrochromic properties of
mesoporous tungsten oxide J. Mater. Chem. 11, 92-97.(2001).
[71]. Y. Djaoued et.al Electrochromic Devices Based on Porous
Tungsten Oxide Thin Films Hindawi Publishing Corporation
Journal of Nanomaterials, Article ID 674168, 9 pages (2012)
[72]. P N. Bhosale et.al, Enhanced electrochromic coloration in
Ag nanoparticle decorated WO3 thin films Electrochimica
Acta 102, 358– 368, (2013).
[73]. R. Hurditch, et.al, Electrochromism in hydrated tungsten-
oxide films. Electronic Letters, 1975, 11, 142-144.
[74]. E. Kikuchi et.al, Photochromism and photoelectrochemistry
of amorphous and polycrystalline WO3 films. Journal of
Electrochemical. Society, 351(1-2) ,105-114 (1993).
[75]. C. Sanjeeviraja et.al, Preparation and characterization of
spray deposited n-type WO3 thin films for electrochromic
devices. Materials Research Bullietin, 39(10),1479-1489
(2004).
[76]. P. Schmuki et.al Thick porous tungsten trioxide films by
anodization of tungsten in fluoride containing phosphoric acid
electrolyte Electrochemistry Communications 11 ,1908–
1911(2009).
[77]. R.S.Patil et.al, Electrochromic properties of electrodeposited
tungsten oxide (WO3) thin film, Solid State Physics:
Proceedings of the 56th DAE Solid State Physics Symposium
(2011).
[78]. A. Duta et.al, Synthesis and characterization of WO3
pyrolysis for electrochromic applications thin films by
surfactant assisted spray Materials Chemistry and Physics 140
, 49-59(2013).
[79]. C. Henrist et.al, Improved coloration contrast and
electrochromic efficiency of tungsten oxide films thanks to a
surfactant-assisted ultrasonic spray pyrolysis process Solar
Energy Materials& Solar Cells130,623–628(2014).
[80]. G. Leftheriotis et.al, A simple method for the fabrication of
WO3 and photocatalytic properties films with electrochromic
Thin Solid Films 573 6–13(2014).
[81]. R. Sivakumar et.al, Inorganic Materials: Recent Advances,
Narosa Publishing House, New Delhi ,215pp(2004).
[82]. J. Pankove, Display devices, Applied Physics, 140
,181(1980).
[83]. C. Sanjeeviraja et.al, Studies on the effect of substrate
temperature on (VI–VI) textured tungsten oxide (WO3) thin
films on glass, SnO2:F substrates by PVD:EBE technique for
electrochromic devices. Materials Chemistry and Physics,
87, 439-445 (2004).
[84]. Ki-Tae Lee et.al, Characterization of electrochromic WO3
thin films fabricated by an RF sputtering method. Journal of
Ceramic Processing Research. 14(3),337-341(2013).
[85]. Chin-Guo Kuo et.al, Experimental study of the
electrochromic properties of WO3 thin films derived by
electrochemical method. Journal of Marine Science and
Technology, 20(4) ,365-368 (2012).
[86]. Ko-Wei Weng et.al, Electrochromic properties of tungsten-
titanium oxide films. Journal of Nanoscience and
Nanotechnology, 12, 1296–1300(2012).
[87]. J.T. Chang et.al, Influences of Plasma Parameters on the
Optical Properties of Tungsten Oxide Films Deposited by
Reactive DC Magnetron Sputtering. Surface and Coatings
Technolog ,200( 5–6), 1219-2048(2005).
[88]. M.C Rao et.al, Optical Properties of Vacuum Evaporated
WO3 Thin Films. Research Journal of Chemical Sciences
,2011, 1(7), 76-80.
[89]. H. Kawasaki et.al, Preparation of WO3 Thin Films for
Electrochromic Display by Plasma Process. Journal of Plasma
Fusion Research Series, 1431-1434(2009).
[90]. A. Rougier et.al, Electrochromic activity of template WO3
films tested in ionic liquid. Ionics, 14, 99-105(2008).
[91]. K. Muthu karuppasamy, Studies on the electrochromic and
photocatalytic properties of pure and vanadium doped
tungsten oxide thin films prepared by electron beam
evaporation and dc magnetron sputtering techniques Journal
of Physics D: Applied Physics , 41 035302 (2008).
[92]. J. Augustynski et.al,Electrochromic and
photoelectrochemical characteristics of nanostructured WO3
films prepared by a sol–gel method. Comptes Rendus Chimie
, 9(2), 301–306 (2006).
[93]. B. Almeida et.al, Structural and optical characterization of
WO3 deposited on glass and ITO. Vacuum 64(3–4), 287–
291(2002).
[94]. M. Hepel et.al, Electrochromism in electrodeposited
nanocrystalline WO3 films I. Electrochemical and optical
properties. Journal of New Materials for Electrochemical
Systems, 3, 241-247(2000).
[95]. P.S. Patil et.al,The electrochromic properties of tungsten
oxide thin films deposited by solution thermolysis. Solid State
Ionics, 136–137,.505–511(2000).

REVIEW ARTICLE
[96]. A. Pennisi et.al, Electrochromic properties of tungsten-
molybdenum oxide electrodes. Solar Energy Materials and
Solar Cells, 28(3), 233-247(1992).
[97]. S.Deb, Optical and photoelectric properties and colour centers
in thin films of tungsten oxide. Philosophical Magazine, 27 ,
801-807(1973).
[98]. M. Kaneko et.al, Physical and electrochromic properties of
the amorphous and crystalline tungsten oxide thick films
prepared under reducing atmosphere. Journal of Applied
Physics, 55 , 2747-2752(1984).
[99]. M. Kitao, et.al, Preparation conditions of sputtered
electrochromic WO3 films and their infrared absorption
spectra. Solar Energy Materials and Solar Cells, 25(3-4), 241-
256(1992).
[100]. H.Akram et.al, Preparation and aging of sputtered tungstic
oxide films. Journal of Applied Physics , 62, 2039-2042
(1987).
[101].M. Kitao, et.al, Preparation conditions of sputtered
electrochromic WO3 films and their infrared absorption
spectra. Solar Energy Materials and Solar Cells, 25(34),241-
255(1992).
[102].A. Donnadieu et.al, Structure, optical and electro-optical
properties of polycrystalline WO3 and MoO3 thin films
prepared by chemical vapour deposition. Thin Solid Films,
164, 333-338(1988).
[103].P. Delichere, et.al, Electrochromism in anodic WO3 films II:
Optical and electrochromic properties of coloured “distorted”
hexagonal films. Thin Solid Films, 161, 47-58(1988).
[104].D. V. Sviridov et.al, Electrochemical and Rutherford
backscattering study of thermally crystallized tungsten
trioxide anodic films. Thin Solid Films, 198(1-2), 191-
198(1991).
[105].A. Ogura et.al, Extension of Dose Window for Low‐Dose
Separation by Implanted Oxygen. Journal of the
Electrochemical Society, 145 (5), 1735-1737(1998).
[106].M. Green et.al, Optical properties of dilute hydrogen tungsten
bronze thin films. Journal of Applied Physics, 69 , 7788-
7792(1991).
[107].K. von Rottkay et.al, Analysis of binary electrochromic
tungsten oxides with effective medium theory. Thin Solid
Films, 308 -309, 50-55(1997).
[108].A Temmink, et.al , 4f level shifts of tungsten and colouration
state of a-WO3. Vacuum, 41(4-6) ,1144-1446(1990).
[109].C.G. Granqvista et.al, Electrochromism of W-oxide-based
thin films: Recent advances. Solid Stale Ionics, 86-88(2) ,
943-948 (1996).
[110].S. F. Cogan et.al, Free‐electron electrochromic modulation in
crystalline Li x WO3. Journal of Applied Physics, 60, 2735-
2739(1986).
[111].F. O. Arntz et.al, Near‐infrared reflectance modulation with
electrochromic crystalline WO3 films deposited on ambient
temperature glass substrates by an oxygen ion‐assisted
technique. Journal of Applied Physics, 67 , 3177-3182(1990).
[112]. S.J. GOLDEN et.al, Thin-film tin-doped indium oxide
counter-electrode for electrochromic applications. Solid State
Ionics, 28-30(2),1733-1737(1988).
[113].M. Hutchins et.al, Optimisation of Preparative and
Performance Parameters on Electrochromic Properties of
Electrochemically Deposited Tungsten Oxide Films.
Japanese Journal Applied Physics, 37(1-9A) 48l2, (l998)
[114]. P.V. Ashrit et.al, Electrochromic properties of
nanocrystalline tungsten oxide thin films. Thin Solid Films,
320, 324-328 (1998).
BIOGRAPHY
Vyomesh R Buch is working as an Assistant
Professor at Department of Mechanical
Engineering, Babaria Institute of
Engineering and Technology. Varanama. He
did his Masters in Metallurgy with
specialization in Materials Technology from
Faculty of Engineering & Technology,
Vadodara. His current research interests are
nanocomposites, nanostructures, synthesis and characterization of
thin films and coatings

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