Study of the electrical characteristics of polyaniline ... - CyberLeninka

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Energy Procedia 19 (2012) 71 – 79

Study of the electrical characteristics of polyaniline prepeared by electrochemical polymerization Kareema. M. Ziadan a, Wjood T.Saadonb

a* a

Department of physics,College of Science University of Basra, Iraq

b

Ministry of oil Petroleum Company, Southern Area, Basrah – Iraq

Abstract

Polyaniline (PAni) is one of imported polymer for synthesis solar cells .The quality of film depended on the method of polymerization. In this research PAni have been prepared by the electrochemical polymerization of aniline on stainless steel electrode. The electrical conductivity of these films was measured by two–probe method .The electrical conductivity is influenced by preparation conduction such as concentration of H2SO4 and current density .The conductivity between (0.1 - 10-10) S/cm depends on PH and current density . The best electrical conductivity about (0.1) S/cm was found PH at (4.2) and current density 0.3mA/cm2. . © Elsevier Ltd.Ltd. Selection and/or peer review under responsibility of The MEDGREEN Society. © 2012 2010Published Publishedbyby Elsevier Selection and/or peer-review under responsibility of [name organizer]

Keywords: Solar cells, polyaniline,electrochemical polymerization, electrical characterisation,. 1.Introduction Organic semiconductors have attracted great attention in the field of active materials for solar cell applications such as in organic light emitting diodes (OLEDs)1 , field-effect transistors

* Corresponding author. Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 . E-mail address: [email protected].

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K.M. Ziadan and W.T.Saadon / Energy Procedia 19 (2012) 71 – 79

(OFETs) 2 and solar cells3-7 . Polyaniline (PAni) is one of the most promising conducting polymers8-10 . The most important feature that makes PAni so interesting as sensitive p-n junction layer for the solar cell is the variation of its electrical and optical properties at room temperature 11,12 Polyaniline (PAni) is one of (ICP) and an attractive due to its considerable conductivity, easy synthesis route and good thermal stability. The .conductivity could be increased by more than ten orders of magnitude by doping with protonic acids13. Depending on the oxidation level, PAni can be synthesized in various insulating forms such as the fully reduced leucoemeraldine base (LEB), the half oxidized emeraldine base (PAni EB)] and the fully oxidized pernigraniline base (PNB) 14,-16. Of these three forms PAni EB is the most stable and widely investigated polymer in this family. PAni EB differs substantially from LEB and PNB in the sense that its conductivity can be tuned via doping from 10-10 S/cm up to 100 S/cm and more where as the LEB and PNB forms can not be made conducting9. The insulating emeraldine base form of polyaniline (PAni EB) consists of equal numbers of reduced [-(C6H4)-N(H)-(C6H4)-N(H)-] and oxidized [-(C6H4)-N=(C6H4)=N-] as show in figure (1). In the present study polyaniline films have been Prepared by electrochemical polymerization of aniline monomer and electrolyte containing different concentration ratios (PH) of H2So4. The polymer films have been characterizers by Infra-red IR spectrophotometer . The conductivity measured by two probe method16.

Figure 1 (a) Insulating emeraldine base form of PANi, (b) conducting emeraldine salt form of PANi

2. Experimental 2.1 Films preparation polyaniline PAni prepared by electrochemical polymerization of aniline on stainless steel . The electrochemical cell consisting of working and counter electrodes of stainless steel and electrolyte solution. The aniline was distilled under reduced pressure and stored in darkness before use, H2SO4 and purified double distilled water were used in preparing the electrolyte solution. The Polymerization was carried out at different current densities from (0.001 to 1) mA/cm2. The best condition for the preparing film was at current density 0.3mA/cm2, and Polymerization time about 25 min. The electrical conductivity influenced by ( concentration ) PH of H2SO4 . So the films were prepared at different PH (from 2.5 to 6.5) in order to have doped and undoped PAni .The electrochemical polymerization method and preparation techniques have been described by 16 .

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2.2The electrical measurement The electrical conductivity measurement for the conducting polymers films were calculated by two- probe method, The two-probe method was explained by wejood15. The thickness of the films was measured by using Faradays law 16. 3.Results and Discussion The characterization of undoped (PAni) films have been curried out using IR analyzing technique as shown figure (2) and for doped PAni in figure(3).Table(1) tabulated the wave vector of functional groups of PAni. That have the same groups of other 16-20

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Table (1) The functional groups of PAni

N-H

C=N

C=C

C-N

SO4

C-H

C-S

functional groups of PAni

‫ـــــــ‬

functionagroups of undPAni cm-1

425

functionagroups of undPAni cm-1 cm-

780

‫ــــــــ‬

Ref.18

‫ــــــــــ‬

820

496

Ref.19

‫ـــــــــــ‬

780

‫ـــــــــ‬

Ref.20 ◌ٍ

3300

1720 1630

1450 1610

1390

‫ــــــ‬

780 3200

3300

1630

1450 1605

1390

1100 1160

780

3200

1625

‫ــــــــ‬

1310

1120

‫ـــــــــــ‬

1705

1491 1558

1294

3200

1720

1490 1610

1390

The quality of the film was examined by the measurement of conductivity as a function of current density as shown in Figure(4).The best conductivity about (0.1) S/cm2 at current density 0.3 mA/cm2,this was carried out at PH( 4 - 4.5 ) . At values of current density higher than the characterized, the conductivity have lower values as indicated in figure (4).This coued be attributed to the low value of current density which is not sufficient to give high doped (PAni- H2SO4 ),while high values of current density lead to low conductivity because the high values of current density make the polymerization too fast so that some polymer fragments fall in solution .

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1.00E+00

1.00E-01

1.00E-02

1.00E-03

1.00E-04

1.00E-05 1.00E-03

1.00E-02

1.00E-01

1.00E+00

1.00E+01

Figure(4) conductivity as a function of current density

Figure (5) show the conductivity as a function of PH degree (concentration of H2SO4) .The electrical conductivity increase as PH increased ,when reached to( 4.2) the conductivity became (0.1)S/cm ,then decreased to (1.5x10 -10) S/cm at PH ( 6) the curve can be divided in to three regions one region when PH less than 4 the conductivity is low because small PH gives (reduced stat) PAni can not doped with H2SO4 (low doping) 8,10 .The second region at ( 4 - 4.2) PH, the electrical conductivity is large , i.e. PAni doped with H2SO4 (high oxidation),while third region at PH higher than 4.5 the conductivity decrease because PAni can not doped with (H2SO4) 16.


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1 .0 0 E + 0 0

1 .0 0 E - 0 1

1 .0 0 E - 0 2

1 .0 0 E - 0 3

σ(S/cm

1 .0 0 E - 0 4

1 .0 0 E - 0 5

1 .0 0 E - 0 6

1 .0 0 E - 0 7

1 .0 0 E - 0 8

1 .0 0 E - 0 9

1 .0 0 E - 1 0

0

1

2

3

4

5

6

7

8

pH Figure (5) conductivity as a function of PH

Figure (6) shows the electrical conductivity as a function of polymerization time for PAni prepared at 4 PH. The electrical conductivity increases as polymerization time increases until reach to 25 min the conductivity became constant at 0.1 S/cm ,thiscan be explain ,this time is enough to complete 16 polymerization i.e to reach the maximum value for doping .

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4. Conclusion The electrical conductivity of PAin is influenced by the synthesis conditions such as current density ,PH degree and polymerization time. The best electrical conductivity was found at PH degree ( 44.5)corresponding to current density 0.3 mA/cm2and polymerization time 25 min

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