We have prepared an all-solid-thin film electrochromic device (ECD), consisting of layers ITO / NiO / ZrO2 / WO3 / ITO using the PVD method. The WO3 is used as an electrochromic layer, NiO as an ion-storage layer, and ZrO2 as a solid electrolyte layer in the all-solid-thin film ECD. The optical transmittance varied between 3-59 %. The device shows the coloration and bleaching time of 120 s and 2 s, respectively, with a good memory effect and desirable cycle-life.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3101

Deota, H.N.

Desai, M.S.

Panchal, C.J.

Patel, K.J.

Trivedi, U.B.

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 5 No 2, 02023(3pp) (2013) Том 5 № 2, 02023(3cc) (2013) 
 
 
2077-6772/2013/5(2)02023(3) 02023-1  2013 Sumy State University 
All-Solid-Thin Film Electrochromic Devices Consisting of Layers ITO / NiO / ZrO2 / WO3 / ITO 
 
K.J. Patel1, M.S. Desai1, C.J. Panchal1,*, H.N. Deota1, U.B. Trivedi2 
 
1 Applied Physics Department, Faculty of Technology and Engineering, The M.S. University of Baroda,  
Vadodara-390001 Gujarat, India 
2 Department of Electronics, Sardar Patel University, Vallabh Vidhyanagar-380120, India 
 
(Received 15 February 2013; published online 04 May 2013) 
 
We have prepared an all-solid-thin film electrochromic device (ECD), consisting of layers 
ITO / NiO / ZrO2 / WO3 / ITO using the PVD method. The WO3 is used as an electrochromic layer, NiO as 
an ion-storage layer, and ZrO2 as a solid electrolyte layer in the all-solid-thin film ECD. The optical trans-
mittance varied between 3-59 %. The device shows the coloration and bleaching time of 120 s and 2 s, re-
spectively, with a good memory effect and desirable cycle-life. 
 
Keywords: Physical vapor deposition, Electrochromic device, Transmission modulation  
 
 PACS numbers: 81.15.Ef, 85.60.Pg, 78.20.Ci 
 
 
                                                          
* cjpanchal_msu@yahoo.com 
1. INTODUCTION 
 
Electrochromic devices (ECD) are of considerable in-
terest in many commercial applications due to their con-
trollable transmission, absorption, and/or reflectance [1, 
2]. The electrochromic (EC) phenomenon occurs due to 
the electrochemical redox reactions that take place in 
EC materials. There are many possible ECD structures 
reported in the literature [3, 4]. The ECD structure may 
have five layers (transparent conducting oxide (TCO) 
layer / ion-storage layer (IS) / solid electrolyte / EC lay-
er / TCO layer) superimposed on one substrate or may be 
positioned between two substrates in the laminate con-
figuration. On one side of the EC layer there is an ion-
conducting layer and on the other side of it there is an 
ion-storage layer. In the complementary ECD structure 
both EC and ion-storage electrode layer show EC proper-
ties, one of them colored anodically while the other is 
colored cathodically. In such a device structure both lay-
ers are colored and bleached simultaneously, thus the 
optical modulation increases. Tungsten oxide (WO3) is 
used as a cathodic coloration material [5] and Nickel 
oxide (NiO) is used as an anodic coloration material [6], 
because both materials show good EC properties [7, 8]. 
During the EC coloration and bleaching processes the 
following electrochemical reactions take place in WO3 
and NiO layers: 
 
 
1
3 3
( ) ( )
xWO xe xM M WO
Colorless Blue
 (1) 
 
 
2
( ) ( )
( )
( ) ( )
NiO OH NiOOH e
Bleached Colored
OR
Ni OH NiOOH H e
Bleached Colored
 (2) 
 
Zirconium oxide (ZrO2) thin film is used as a “pro-
ton conducting” solid electrolyte [9] and Indium tin 
oxide (ITO) is used as a transparent conducting elec-
trode [10]. A number of physical vapor deposition 
methods are reported for the deposition of the different 
thin film layers for the ECD structure. 
In the present paper, we have prepared all-solid-
thin film complimentary ECD structure consisting of 
layers ITO / NiO / ZrO2 / WO3 / ITO on a glass sub-
strate using physical vapor deposition. The characteris-
tic of the ECD devices like optical modulation, memory 
effect, switching time, and cycle-life are presented. 
 
2. ECD FABRICATION 
 
The different layers of all-solid-thin film ECD are 
deposited by different physical vapor deposition tech-
niques in a high vacuum coating unit. The Indium tin 
oxide (ITO) thin films, having a sheet resistance of 5-
10 Ω/□, are deposited at room temperature (RT) by RF 
magnetron sputtering on organically cleaned glass sub-
strate [11]. Subsequently, NiO (250 nm) and ZrO2 thin 
film (500 nm) are deposited by e-beam evaporation 
method on the ITO coated substrate held at 200 °C and 
RT, respectively. H+ ions are injected into the NiO film, 
via ZrO2 / NiO / ITO film structure by electrochemically 
cycling it in 0.1 M KOH electrolyte. After removing the 
film structure from the KOH electrolyte it is washed 
with distilled water to get rid of KOH and dried using 
dry air. Now the WO3 thin film (250 nm) is deposited 
by thermal evaporation method on the above structure 
at 200 °C temperature. Finally, the ITO thin film is 
deposited on top of the above device structure. 
The substrate was continuously rotated at 
40 revolutions per minute (rpm) during the deposition 
to improve the film’s uniformity. A frame-shaped shad-
ow mask having an area 2  2 cm2 is used to avoid 
short-circuiting between the different layers from the 
edge. The final configuration of the multilayered ECD 
structure is shown in Fig. 1. 
The ECD can be characterized by the following: 
transmittance modulation, open-circuit memory effect, 
switching time, and cycle-life. The transmittance modu-
lation of the ECD is measured by applying a constant 
voltage between both ITO electrodes to color and to  
 K.J. PATEL, M.S. DESAI, C.J. PANCHAL, ET AL. J. NANO- ELECTRON. PHYS. 5, 02023 (2013) 
 
 
02023-2 
WO3
NiO
ITO on glass
ZrO2
ITO
Top View
Glass Substrate
Side View  
 
Fig. 1 – A schematic diagram of the ECD’s structure with a 
frame-shaped shadow mask 
 
bleach the device and concomitantly measuring the 
transmission spectra in 450-1100 nm wavelength rang-
es for both fully colored and bleached states. For the 
open-circuit memory effect measurement, a voltage 
pulse was applied for the coloration of the device and at 
the same time measured the optical transmittance spec-
tra in an open-circuit condition. A square-wave pulse 
voltage was applied to the device for evaluating the 
switching time of the ECD and concurrently the optical 
measurements were performed using a laser diode 
(650 nm) and a Si photo-detector. For the cycle-life time 
measurement of the device, it was subjected to continu-
ally color-bleach cycling in the same way as for the 
switching time measurement. 
 
3. RESULTS AND DISCUSSIONS  
 
The transmittance modulation (i.e. change in the 
transmittance of bleached (Tb) and the colored (Tc) state 
of the ECD) is measured by applying a constant voltage 
(  5 V) for color and bleach states of the device. When a 
positive potential is applied to the bottom ITO film, the 
color changes to dark from transparent and when a neg-
ative potential is applied, the color changes to transpar-
ent reversibly. During coloration, H+ ions are intercalat-
ed electrochemically into the WO3 film from NiO film via 
ZrO2 electrolyte, while during the bleaching process H+ 
ions are de-intercalated from the WO3 thin film. The 
wavelength-dependence of the optical transmittance 
spectra in 400-1100 nm range for the as-deposited, col-
ored, and bleached states of devices are presented in 
Fig. 2. The ECD shows 56 % transmission modulation 
with 59 % transmittance in bleach state and 3 % in co-
lored state. 
The memory effect is one of the excellent benefits of 
ECD. Open-circuit memory effect is defined as the time 
duration in which the material remains in steady state 
even after switching off the applied voltage. In the 
bleached state, the WO3 and NiO thin film layers are 
electrochemically stable and thus no change is observed 
if ECD is initially in the bleached state. In this experi-
ment, we applied a voltage of + 5 V for the coloration of 
the device and then measured the optical behavior in an 
open-circuit condition. The transmittance of the device 
was monitored after various open-circuit times and is 
presented in Fig. 3. 
As shown in the Fig. 3, if the ECD is initially in the 
colored state, the transmittance of the device increases 
with time and reaches the bleach state. The ECD 
showed excellent long-term memory, with transmittance 
in colored state below 3 %, and the colored state re-
mained constant up to 20 % after 170 min. This open 
circuit memory loss of the ECD was observed due to 
short-circuiting between WO3 and NiO layer originating  
W a v e le n g th  (n m )
4 5 0 5 0 0 5 5 0 6 0 0 6 5 0 7 0 0 7 5 0 8 0 0 8 5 0 9 0 0 9 5 0 1 0 0 0 1 0 5 0 1 1 0 0
T
r
a
n
s
m
it
t
a
n
c
e
 (
%
)
0
2 0
4 0
6 0
8 0
1 0 0
A s -d e p o s ite d
C o lo r
B le a c h
 
 
Fig. 2 – The transmittance spectra in the as-deposited color 
and bleach states of ECD 
 
W a v e le n g th  (n m )
4 5 0 5 0 0 5 5 0 6 0 0 6 5 0 7 0 0 7 5 0 8 0 0 8 5 0 9 0 0 9 5 0 1 0 0 0 1 0 5 0 1 1 0 0
T
r
a
n
s
m
it
t
a
n
c
e
 (
%
)
0
2 0
4 0
6 0
8 0
1 0 0
A s  d e p o s ite d  
c o lo r  
0  s  
5  s  
1 0  s  
2 0  s  
3 0  s  
6 0  s  
2  m in  
3  m in
4  m in  
5  m in  
6  m in  
7  m in  
8  m in  
9  m in  
1 0  m in  
2 0  m in  
3 0  m in  
4 0  m in  
5 0  m in  
6 0  m in  
7 0  m in  
8 0  m in  
9 0  m in  
1 0 0  m in  
1 1 0  m in  
1 2 0  m in  
1 3 0  m in  
1 4 0  m in  
1 5 0  m in  
1 6 0  m in  
1 7 0 m in  
 
 
Fig. 3 – The change in the optical transmittance with time in 
open circuit conditions of ECD 
 
from “pin-holes”, which is produced during ZrO2 film 
depositions or oxidation and reduction (de-intercalation 
and intercalation) of WO3 and NiO, respectively [12]. 
The switching and stability of the devices were 
measured by applying a square-wave voltage to the de-
vice. In addition, concurrently, the variation in the opti-
cal transmittance with time was recorded. Fig. 4 shows 
the transmittance versus time, at 650 nm wavelength, 
subjected to different square-wave potentials at intervals 
of 60 s. The switching time, at 650 nm wavelength, is 
estimated from Fig. 4 for ECD under various applied 
voltages. The change in transmittance takes place with-
in a few tenths of a second after application of the volt-
age pulse but coloration does not reach saturation even 
after several minutes. 
The transmission modulation increases with increase 
in applied voltage. The maximum transmittance change 
was observed for an applied voltage of  5 V with colora-
tion and bleaching time of 120 and 2 s, respectively. The 
photographs of the corresponding colored and bleached 
state are presented in Fig. 5. The application of high 
voltage leads to fast coloration but also increases the 
possibility of side reaction, and thereby reducing the 
device’s performance and the life. Appling a low voltage 
makes switching safer, thereby increasing the life of the 
devices but the switching time increases and the optical  
 ALL-SOLID-THIN FILM ELECTROCHROMIC DEVICES … J. NANO- ELECTRON. PHYS. 5, 02023 (2013) 
 
 
02023-3 
Time (s)
0 60 120 180 240
T
ra
n
sm
it
ta
n
ce
 (
%
) 
0
20
40
60
80
100
1V 
2V 
3V 
4V 
5V 
 
 
Fig. 4 – The variation in the optical transmittance at 650 nm 
wavelength at various applied voltages 
 
 
a 
 
b 
 
Fig. 5 – The photographs of the bleached (a), and colored (b) 
state of ECD 
 
modulation is also less compared to that at a higher 
voltage. Thus, it is important to optimize the device’s 
operating voltage to achieve a reasonable switching time 
and an optical modulation with a better lifetime. 
For the cycle-life measurement of the device, the 
device was continually subjected to color-bleach cycles 
by application of  5 V at intervals of 60 s. Fig. 6 shows 
the color bleach cycle of transmittance modulation of 
ECD with time. One can see that there was no obvious  
Time (s)
0 5000 10000 15000 20000 25000
T
r
a
n
sm
it
ta
n
c
e
 (
%
)
0
10
20
30
40
50
60
70
80
90
100
 
 
Fig. 6 – The transmittance modulation of ECD with time 
 
decrease in transmittance modulation (60 %-20 %) even 
after 225 cycles or more, which indicates that this ECD 
has a good stability. Furthermore, the degradation of 
the device could not be observed until after a long time 
operation. 
 
4. CONCLUSIONS  
 
We have made an effort to fabricate all-solid-thin 
film ECD having a structure of 
ITO / NiO / ZrO2 / WO3 / ITO on a glass substrate. The 
ECD shows good transmittance modulation (56 %) in 
wavelength range of 450-1000 nm with good open-
circuit memory effect of 170 min. The ECD has colora-
tion and bleaching time of 120 s and 2 s, respectively, 
with a desirable cycle-life. 
 
AKNOWLEDGEMENTS 
 
Authors are thankful to UGC-DRS (file no. 
530/2/DRS/2007(SAP-1)) for providing an electrical 
measurement facility. 
 
 
REFERENCES 
 
1. K. Tajima, H. Hotta, Y. Yamada, M. Okada, 
K. Yoshimura, Appl. Phys. Lett. 100, 091906 (2012). 
2. P. Bonhote, E. Gogniat, F. Campus, L. Walder, M. Gratzel, 
Displays 20, 137 (1999). 
3. C.G. Granqvist, Handbook of Inorganic Electrochromic 
Materials (Amsterdam: Elsevier: 1995). 
4. J.P. Cronin, T.J. Gudgel, S.R. Kennedy, A. Agrawal, 
D.R. Uhlmann, Mater. Res. 2, 1 (1999). 
5. K.J. Patel, C.J. Panchal, M.S. Desai, P.K. Mehta, Mater. 
Chem. Phys. 124, 884 (2010). 
6. K.J. Patel, C.J. Panchal, M.S. Desai, P.K. Mehta, J. Nano- 
Electron. Phys. 3, 362 (2011). 
7. E. Avendano, L. Berggren, G.A. Niklasson, C.G. Granqvist, 
A. Azens, Thin Solid Films 496, 30 (2006). 
8. G.A. Niklasson, C.G. Granqvist, J. Mater. Chem. 17, 127 
(2007). 
9. H.N. Cui, Manuel F. Costa, V. Teixeira, I. Porqueras, 
E. Bertran, Surf. Sci. 532, 1127 (2003). 
10. C.G. Granqvist, A. Hultaker, Thin Solid Films 411, 1 
(2002). 
11. K.J. Patel, M.S. Desai, C.J. Panchal, J. Mater. Sci: Mater. 
Electron 22, 8, 959 (2011). 
12. A.-L. Larsson, G.A. Niklasson, Sol. Energ. Mat. Sol. C. 84, 
351 (2004). 
 


English

All-Solid-Thin Film Electrochromic Devices Consisting of Layers ITO / NiO / ZrO2 / WO3 / ITO

Electronic Sumy State University Institutional Repository

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ Vol. 5 No 2, 02023(3pp) (2013) Том 5 № 2, 02023(3cc) (2013)   2077-6772/2013/5(2)02023(3) 02023-1  2013 Sumy State University All-Solid-Thin Film Electrochromic Devices Consisting of Layers ITO / NiO / ZrO2 / WO3 / ITO  K.J. Patel1, M.S. Desai1, C.J. Panchal1,*, H.N. Deota1, U.B. Trivedi2  1 Applied Physics Department, Faculty of Technology and Engineering, The M.S. University of Baroda,  Vadodara-390001 Gujarat, India 2 Department of Electronics, Sardar Patel University, Vallabh Vidhyanagar-380120, India  (Received 15 February 2013; published online 04 May 2013)  We have prepared an all-solid-thin film electrochromic device (ECD), consisting of layers ITO / NiO / ZrO2 / WO3 / ITO using the PVD method. The WO3 is used as an electrochromic layer, NiO as an ion-storage layer, and ZrO2 as a solid electrolyte layer in the all-solid-thin film ECD. The optical trans-mittance varied between 3-59 %. The device shows the coloration and bleaching time of 120 s and 2 s, re-spectively, with a good memory effect and desirable cycle-life.  Keywords: Physical vapor deposition, Electrochromic device, Transmission modulation    PACS numbers: 81.15.Ef, 85.60.Pg, 78.20.Ci                                                             * cjpanchal_msu@yahoo.com 1. INTODUCTION  Electrochromic devices (ECD) are of considerable in-terest in many commercial applications due to their con-trollable transmission, absorption, and/or reflectance [1, 2]. The electrochromic (EC) phenomenon occurs due to the electrochemical redox reactions that take place in EC materials. There are many possible ECD structures reported in the literature [3, 4]. The ECD structure may have five layers (transparent conducting oxide (TCO) layer / ion-storage layer (IS) / solid electrolyte / EC lay-er / TCO layer) superimposed on one substrate or may be positioned between two substrates in the laminate con-figuration. On one side of the EC layer there is an ion-conducting layer and on the other side of it there is an ion-storage layer. In the complementary ECD structure both EC and ion-storage electrode layer show EC proper-ties, one of them colored anodically while the other is colored cathodically. In such a device structure both lay-ers are colored and bleached simultaneously, thus the optical modulation increases. Tungsten oxide (WO3) is used as a cathodic coloration material [5] and Nickel oxide (NiO) is used as an anodic coloration material [6], because both materials show good EC properties [7, 8]. During the EC coloration and bleaching processes the following electrochemical reactions take place in WO3 and NiO layers:   13 3( ) ( )xWO xe xM M WOColorless Blue (1)   2( ) ( )( )( ) ( )NiO OH NiOOH eBleached ColoredORNi OH NiOOH H eBleached Colored (2)  Zirconium oxide (ZrO2) thin film is used as a “pro-ton conducting” solid electrolyte [9] and Indium tin oxide (ITO) is used as a transparent conducting elec-trode [10]. A number of physical vapor deposition methods are reported for the deposition of the different thin film layers for the ECD structure. In the present paper, we have prepared all-solid-thin film complimentary ECD structure consisting of layers ITO / NiO / ZrO2 / WO3 / ITO on a glass sub-strate using physical vapor deposition. The characteris-tic of the ECD devices like optical modulation, memory effect, switching time, and cycle-life are presented.  2. ECD FABRICATION  The different layers of all-solid-thin film ECD are deposited by different physical vapor deposition tech-niques in a high vacuum coating unit. The Indium tin oxide (ITO) thin films, having a sheet resistance of 5-10 Ω/□, are deposited at room temperature (RT) by RF magnetron sputtering on organically cleaned glass sub-strate [11]. Subsequently, NiO (250 nm) and ZrO2 thin film (500 nm) are deposited by e-beam evaporation method on the ITO coated substrate held at 200 °C and RT, respectively. H+ ions are injected into the NiO film, via ZrO2 / NiO / ITO film structure by electrochemically cycling it in 0.1 M KOH electrolyte. After removing the film structure from the KOH electrolyte it is washed with distilled water to get rid of KOH and dried using dry air. Now the WO3 thin film (250 nm) is deposited by thermal evaporation method on the above structure at 200 °C temperature. Finally, the ITO thin film is deposited on top of the above device structure. The substrate was continuously rotated at 40 revolutions per minute (rpm) during the deposition to improve the film’s uniformity. A frame-shaped shad-ow mask having an area 2  2 cm2 is used to avoid short-circuiting between the different layers from the edge. The final configuration of the multilayered ECD structure is shown in Fig. 1. The ECD can be characterized by the following: transmittance modulation, open-circuit memory effect, switching time, and cycle-life. The transmittance modu-lation of the ECD is measured by applying a constant voltage between both ITO electrodes to color and to   K.J. PATEL, M.S. DESAI, C.J. PANCHAL, ET AL. J. NANO- ELECTRON. PHYS. 5, 02023 (2013)   02023-2 WO3NiOITO on glassZrO2ITOTop ViewGlass SubstrateSide View   Fig. 1 – A schematic diagram of the ECD’s structure with a frame-shaped shadow mask  bleach the device and concomitantly measuring the transmission spectra in 450-1100 nm wavelength rang-es for both fully colored and bleached states. For the open-circuit memory effect measurement, a voltage pulse was applied for the coloration of the device and at the same time measured the optical transmittance spec-tra in an open-circuit condition. A square-wave pulse voltage was applied to the device for evaluating the switching time of the ECD and concurrently the optical measurements were performed using a laser diode (650 nm) and a Si photo-detector. For the cycle-life time measurement of the device, it was subjected to continu-ally color-bleach cycling in the same way as for the switching time measurement.  3. RESULTS AND DISCUSSIONS   The transmittance modulation (i.e. change in the transmittance of bleached (Tb) and the colored (Tc) state of the ECD) is measured by applying a constant voltage (  5 V) for color and bleach states of the device. When a positive potential is applied to the bottom ITO film, the color changes to dark from transparent and when a neg-ative potential is applied, the color changes to transpar-ent reversibly. During coloration, H+ ions are intercalat-ed electrochemically into the WO3 film from NiO film via ZrO2 electrolyte, while during the bleaching process H+ ions are de-intercalated from the WO3 thin film. The wavelength-dependence of the optical transmittance spectra in 400-1100 nm range for the as-deposited, col-ored, and bleached states of devices are presented in Fig. 2. The ECD shows 56 % transmission modulation with 59 % transmittance in bleach state and 3 % in co-lored state. The memory effect is one of the excellent benefits of ECD. Open-circuit memory effect is defined as the time duration in which the material remains in steady state even after switching off the applied voltage. In the bleached state, the WO3 and NiO thin film layers are electrochemically stable and thus no change is observed if ECD is initially in the bleached state. In this experi-ment, we applied a voltage of + 5 V for the coloration of the device and then measured the optical behavior in an open-circuit condition. The transmittance of the device was monitored after various open-circuit times and is presented in Fig. 3. As shown in the Fig. 3, if the ECD is initially in the colored state, the transmittance of the device increases with time and reaches the bleach state. The ECD showed excellent long-term memory, with transmittance in colored state below 3 %, and the colored state re-mained constant up to 20 % after 170 min. This open circuit memory loss of the ECD was observed due to short-circuiting between WO3 and NiO layer originating  W a v e le n g th  (n m )4 5 0 5 0 0 5 5 0 6 0 0 6 5 0 7 0 0 7 5 0 8 0 0 8 5 0 9 0 0 9 5 0 1 0 0 0 1 0 5 0 1 1 0 0Transmittance (%)02 04 06 08 01 0 0A s -d e p o s ite dC o lo rB le a c h  Fig. 2 – The transmittance spectra in the as-deposited color and bleach states of ECD  W a v e le n g th  (n m )4 5 0 5 0 0 5 5 0 6 0 0 6 5 0 7 0 0 7 5 0 8 0 0 8 5 0 9 0 0 9 5 0 1 0 0 0 1 0 5 0 1 1 0 0Transmittance (%)02 04 06 08 01 0 0A s  d e p o s ite d  c o lo r  0  s  5  s  1 0  s  2 0  s  3 0  s  6 0  s  2  m in  3  m in4  m in  5  m in  6  m in  7  m in  8  m in  9  m in  1 0  m in  2 0  m in  3 0  m in  4 0  m in  5 0  m in  6 0  m in  7 0  m in  8 0  m in  9 0  m in  1 0 0  m in  1 1 0  m in  1 2 0  m in  1 3 0  m in  1 4 0  m in  1 5 0  m in  1 6 0  m in  1 7 0 m in    Fig. 3 – The change in the optical transmittance with time in open circuit conditions of ECD  from “pin-holes”, which is produced during ZrO2 film depositions or oxidation and reduction (de-intercalation and intercalation) of WO3 and NiO, respectively [12]. The switching and stability of the devices were measured by applying a square-wave voltage to the de-vice. In addition, concurrently, the variation in the opti-cal transmittance with time was recorded. Fig. 4 shows the transmittance versus time, at 650 nm wavelength, subjected to different square-wave potentials at intervals of 60 s. The switching time, at 650 nm wavelength, is estimated from Fig. 4 for ECD under various applied voltages. The change in transmittance takes place with-in a few tenths of a second after application of the volt-age pulse but coloration does not reach saturation even after several minutes. The transmission modulation increases with increase in applied voltage. The maximum transmittance change was observed for an applied voltage of  5 V with colora-tion and bleaching time of 120 and 2 s, respectively. The photographs of the corresponding colored and bleached state are presented in Fig. 5. The application of high voltage leads to fast coloration but also increases the possibility of side reaction, and thereby reducing the device’s performance and the life. Appling a low voltage makes switching safer, thereby increasing the life of the devices but the switching time increases and the optical   ALL-SOLID-THIN FILM ELECTROCHROMIC DEVICES … J. NANO- ELECTRON. PHYS. 5, 02023 (2013)   02023-3 Time (s)0 60 120 180 240Transmittance (%) 0204060801001V 2V 3V 4V 5V   Fig. 4 – The variation in the optical transmittance at 650 nm wavelength at various applied voltages   a  b  Fig. 5 – The photographs of the bleached (a), and colored (b) state of ECD  modulation is also less compared to that at a higher voltage. Thus, it is important to optimize the device’s operating voltage to achieve a reasonable switching time and an optical modulation with a better lifetime. For the cycle-life measurement of the device, the device was continually subjected to color-bleach cycles by application of  5 V at intervals of 60 s. Fig. 6 shows the color bleach cycle of transmittance modulation of ECD with time. One can see that there was no obvious  Time (s)0 5000 10000 15000 20000 25000Transmittance (%)0102030405060708090100  Fig. 6 – The transmittance modulation of ECD with time  decrease in transmittance modulation (60 %-20 %) even after 225 cycles or more, which indicates that this ECD has a good stability. Furthermore, the degradation of the device could not be observed until after a long time operation.  4. CONCLUSIONS   We have made an effort to fabricate all-solid-thin film ECD having a structure of ITO / NiO / ZrO2 / WO3 / ITO on a glass substrate. The ECD shows good transmittance modulation (56 %) in wavelength range of 450-1000 nm with good open-circuit memory effect of 170 min. The ECD has colora-tion and bleaching time of 120 s and 2 s, respectively, with a desirable cycle-life.  AKNOWLEDGEMENTS  Authors are thankful to UGC-DRS (file no. 530/2/DRS/2007(SAP-1)) for providing an electrical measurement facility.   REFERENCES  1. K. Tajima, H. Hotta, Y. Yamada, M. Okada, K. Yoshimura, Appl. Phys. Lett. 100, 091906 (2012). 2. P. Bonhote, E. Gogniat, F. Campus, L. Walder, M. Gratzel, Displays 20, 137 (1999). 3. C.G. Granqvist, Handbook of Inorganic Electrochromic Materials (Amsterdam: Elsevier: 1995). 4. J.P. Cronin, T.J. Gudgel, S.R. Kennedy, A. Agrawal, D.R. Uhlmann, Mater. Res. 2, 1 (1999). 5. K.J. Patel, C.J. Panchal, M.S. Desai, P.K. Mehta, Mater. Chem. Phys. 124, 884 (2010). 6. K.J. Patel, C.J. Panchal, M.S. Desai, P.K. Mehta, J. Nano- Electron. Phys. 3, 362 (2011). 7. E. Avendano, L. Berggren, G.A. Niklasson, C.G. Granqvist, A. Azens, Thin Solid Films 496, 30 (2006). 8. G.A. Niklasson, C.G. Granqvist, J. Mater. Chem. 17, 127 (2007). 9. H.N. Cui, Manuel F. 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All-Solid-Thin Film Electrochromic Devices Consisting of Layers ITO / NiO / ZrO2 / WO3 / ITO

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