ARTICLE IN PRESS

Physica B 404 (2009) 1359–1361

Contents lists available at ScienceDirect

Physica B

0921-45

doi:10.1

� Corr

E-m

journal homepage: www.elsevier.com/locate/physb

Preparation and characterization of PAN based solid polymeric electrolyte fordye-sensitized solar cells

Rika b, A. Ahmad a, M.Y.A. Rahman b,�, M.M. Salleh a

a Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysiab College of Engineering, Universiti Tenaga Nasional, 43009 Kajang, Selangor, Malaysia

a r t i c l e i n f o

Article history:

Received 30 October 2008

Received in revised form

5 December 2008

Accepted 18 December 2008

PACS:

61.82.Pv

64.70.Pf

67.80.Gb

68.60.Dv

Keywords:

PAN–PC–LiClO4

Glass transition temperature

Ionic conductivity

Solution casting

26/$ - see front matter & 2008 Elsevier B.V. A

016/j.physb.2008.12.023

esponding author. Tel.: +60 3 89287262; fax:

ail address: yusri@uniten.edu.my (M.Y.A. Rah

a b s t r a c t

Ionic conductivity of PAN–PC–LiClO4 with propylene carbonate filler as a function of LiClO4

concentration and temperature has been studied. The electrolyte samples were prepared by solution

casting technique. The ionic conductivity was measured using impedance spectroscopy technique. The

electrolyte conductivity increases with LiClO4 concentration and temperature. The conductivity

temperature behavior of the electrolyte is Arrhennian. The highest room temperature conductivity of

the electrolyte of 4.2�10�4 Scm�1 was obtained at 10% by weight of LiClO4. The electrolyte conductivity

has been improved by 60 times by replacing PVC by PAN. The activation energy, Ea and pre-exponential

factor, so are 0.46 eV and 2.0�10�4 Scm�1, respectively. The glass transition temperature of the

electrolyte with 10% and 15% by weight of LiClO4 are 83.7 and 78.8 1C, respectively.

& 2008 Elsevier B.V. All rights reserved.

1. Introduction

In an earlier work, a solid polymeric electrolyte of PVC–LiClO4

with the organic molecules filler of propylene carbonate (PC) hasbeen studied in Ref. [1]. It was then utilized in photoelectro-chemical cells of ITO/TiO2/PVC–LiClO4/graphite. However, theionic conductivity of the electrolyte at the operating temperatureof the device was low. The highest conductivity of the electrolytewas in the order of 10�5 Scm�1. The small cells performance wasdue to the low conductivity of the electrolyte [2]. One way ofimproving the conductivity of the electrolyte is to replace thepolymeric material which serves as a host material for the chargeto move. PAN based solid polymeric electrolyte has been studiedby a lot of groups [3–5]. In this work, we prepared a solidpolymeric electrolyte of PAN–PC–LiClO4 with poly(acronitrile) as ahost material, PC as an organic filler and lithium perchlorate(LiClO4) as an ion source, respectively. As such, it is very useful tostudy the effect of LiClO4 concentration and temperature on theionic conductivity of PAN–PC–LiClO4 electrolyte.

ll rights reserved.

+60 3 89212065.

man).

2. Experimental

2.1. Sample preparation

Two grams of PAN powder was added into 20 ml dimethylfor-mide (DMF) and stirred using a magnetic stirrer. 0.1 g (5% wt)LiClO4 powder was then added into 6.6 ml PC. The two separatesolutions were mixed and heated at 70 1C in atmosphere in orderto fully dissolve PAN and further stirred for 24 hours. Thehomogeneous solution was then poured onto a glass petri-dishand left for slow drying to room temperature to form theelectrolyte film. The electrolyte film was dried in vacuum ovenat 60 1C for 24 hours to remove the residual solvent. The dried filmwas obtained after DMF solvent has completely evaporated. Thefilm was then peeled off from the dish. These steps were repeatedfor preparing PAN–PC–LiClO4 electrolyte with 10% wt, 15% wt, and20% wt LiClO4. The films with thickness of 0.2–0.4 mm were keptin a desiccator for further use. Conductivity measurements wereperformed by sandwiching the electrolyte films between twostainless steel electrodes and mounted onto holder. The scanningfrequencies range from 1 Hz to 1 MHz using high frequencyresonance analyzer (HFRA) model 1255. Initially, the film sampleswere cut into a shaped disk with diameter of 16 mm. The twosamples showing the highest room temperature conductivity

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Rika et al. / Physica B 404 (2009) 1359–13611360

were chosen for the temperature dependence on the conductivitystudy. The impedance measurements were conducted at tem-perature range from 30 to 90 1C at 10 1C intervals. The sampleswere heated in thermostatic oven model ANDO TO 19. Theconductivity, s dependence on temperature, T is given byArrhennius equation for which

s ¼ so expð�Ea=KTÞ

where so, Ea and K are pre-exponential factor, activation energyand Boltzmann, respectively. The values of so and Ea can becomputed from y-axis intersection and the slope of the plot logsversus 1/T, respectively. The conductivity, s dependence ontemperature, T is given by Vogel–Tammann–Fulcher (VTF)equation for which

sðTÞ ¼ AT�1=2 exp½�B=ðT � ToÞ�

where A and B are constants and can be related to the chargecarrier density and the activation energy, respectively. T isabsolute temperature and To is regarded as 50 K below themeasured glass transition temperature, Tg [6]. It was measured bydifferential scanning calorimeter (DSC).

σ (S

cm-1

)

-4.6

-4.4

-4.2

-4.0

-3.8

-3.610 %wt. LiClO415 %wt. LiClO4

3. Results and discussion

Fig. 1 shows the relationship between the conductivity ofPAN–PC–LiClO4 electrolyte and LiClO4 concentrations at roomtemperature. As the concentration of the salt increases, thenumber of charge carrier of Li+ from LiClO4 salt will also increaseand thus improving the conductivity of the electrolyte ofPAN–PC–LiClO4 up to a certain level and then decreases as shownin Fig. 1. The monotically increase in conductivity on LiClO4

doping is due to the increase in the availability of mobile ionswhich is Li+ [7]. From Fig. 1, the lowest conductivity of 3.4�10�6

Scm�1 is obtained at 0% by weight of LiClO4 and the highest valueof 4.2�10�4 Scm�1 is obtained at 10% by weight of LiClO4. It wasfound that this conductivity has been improved by 60 times ifcompared with that of PVC–PC–LiClO4 that was previouslyreported in [1]. Whereas for 15% by weight of LiClO4, theconductivity decreases to 2.3�10�4 Scm�1. This can be due tothe formation of non-conducting ion pairs within the concentra-tion range of the LiClO4 salt. This cause constraint in the polymersegmental motion and might also increase the crystallinity natureof the electrolyte, leading to the decrease in the charge carriermobility [8]. When the salt content in the electrolyte is furtherincreased, the distance between ions will decrease and it willresult in the interaction between ion Li+ and ClO4

� become more

% wt. LiCO4

0

cond

uctiv

ity (S

cm-1

)

0.0000

0.0001

0.0002

0.0003

0.0004

0.0005

5 10 15 20

Fig. 1. Variation of conductivity of PAN–PC–LiClO4 with LiClO4 content.

apparent and the formation of ion pairs eventually occur in theelectrolyte. The formation of complex of PAN–PC–LiClO4 isdescribed by [9] for which,

LiClO4 þ PC! Liþ½PC�ClO4�

Liþ½PC�ClO4� þ2ðCH2CHCNÞn� ! 2ðCH2CHCNÞn�2Liþ½PC�ClO4

�

Fig. 2 shows the results of conductivity dependence on tempera-ture of PAN–PC–LiClO4 with the LiClO4 weight ratio of 10% and15%. In general, the conductivity within the temperature range30–100 1C was high (10�5 Scm�1). The electrolyte conductivitydata can be fitted well in Arrhennius model. These results agreewell with the results reported in Refs. [7,10,11]. The values of so

and Ea can be found from y-axis intersection and the slope of thegraph logs versus 1/T, respectively. The data for activation energy,Ea and pre-exponential factor, so are summarized in Table 1. Bycomparison, these values are not much different. The highest Ea

and so with PVC based electrolyte reported in Ref. [1] are 0.39 eVand 3.5�10�5 Scm�1, respectively. As the temperature increases,the mobility and the dissociation rate of Li+ ion also increase, thusimproving the conductivity of the electrolyte [7,10].

Fig. 3 shows the conductivity dependence on temperature ofPAN–PC–LiClO4 with the LiClO4 weight ratio of 10% and 15% byVTF model. The electrolyte conductivity does not fit well in VTFmodel. Thus, the constant related to the charge carrier density,A and that of the activation energy, B of the electrolyte cannot beestimated from the graph. Fig. 4 show DSC thermograph forPAN–PC–LiClO4 electrolyte with 10% wt and 15% wt LiClO4. Theglass transition temperatures for these two samples wereobserved at the midpoint of the endothermic peak of thethermographs. The glass transition temperature of the electrolytewith 10% and 15% by weight of LiClO4 are 83.7 and 78.8 1C,respectively. These values were then used to fit in VTF model forthe electrolyte conductivity as shown in Fig. 3.

1000/T (K-1)2.6

log

-5.4

-5.2

-5.0

-4.8

2.8 3.0 3.2 3.4 3.6

Fig. 2. Arrhennius plot for variation of conductivity of PAN–PC–LiClO4.

Table 1Activation energy, Ea and pre-exponential factor, so for the electrolyte.

% weight of LiClO4 Ea (eV) so (Scm�1)

10 0.46 2.0�10�4

15 0.34 1.4�10�4

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0

log(

σT1/

2 ) (S

cm-1

K1/

2 )

-4.0

-3.8

-3.6

-3.4

-3.2

-3.0

-2.8

-2.6

-2.4

10 % wt. LiClO415 % wt. LiClO4

1000/(T-To) (K-1)

20 40 60 80 100 120 140 160

Fig. 3. VTF plot for variation of conductivity of PAN–PC–LiClO4 with temperature.

Temperature (°C)

10 % wt. LiClO4

15 % wt. LiClO4 Tg

0 °C20 10 30 40 50 60 70 80 90 100 110

Fig. 4. DSC thermograph for the electrolyte with 10% wt and 15% wt LiClO4.

Rika et al. / Physica B 404 (2009) 1359–1361 1361

4. Conclusions

We have successfully prepared a solid polymeric electrolyteof PAN–PC–LiClO4 with PAN as a host material of the electrolyte.

The electrolyte conductivity has been improved by about 102

order by replacing PVC by PAN and has potential application indye-sensitized solar cell. The electrolyte conductivity varies withLiClO4 concentration. The results show that the electrolyteconductivity may be explained by Arrhennius model not Vogel–Tammann–Fulcher (VTF) model. Thus, the conductivity tempera-ture behavior of the electrolyte is Arrhennian. The highest roomtemperature conductivity of the electrolyte of 4.2�10�4 Scm�1 isobtained for 10% by weight of LiClO4. The activation energy, Ea andpre-exponential factor, so are 0.46 eV and 2.0�10�4 Scm�1,respectively.

Acknowledgments

The authors are very thankful to School of Food Technologyand Chemical Sciences, Faculty of Science and Technology, UKMfor sample preparation and characterization. This work wasfunded by MOSTI under the eScience Grant no. 03-02-03-SF0080.

References

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