Effect of addition of poly(ethylene glycol) on electrical conductivity of poly(3,4-ethylenedioxythio

REPORTSChinese Science Bulletin2003 Vol. 48 No. 22 2444 " -2445These investigations were not reported before.Effect of addition of poly-1 Experiment(_ i) Reagents and instruments. PEDOT-PSS aque-(ethylene glycol) on electricalous dispersion (rade name: Baytron P) was purchasedconductivity of poly(3,4-from Bayer AG. Poly(ethylene glycol)s (MW= 400, 800,2000, A.R.) were received from Merck Schuchardt. Elc-ethylenedioxythiophene)-trical conductivity of thin films was measured by Advan-test R6142 program-mable DC potential gavanostaticpoly(styrenesulfonate) hybridgenerator and Keithley 196 multimeter. Films thicknesswas measured by thickness indicator No.2 optics instru-WANG Tiejun, QI Yingqun, XU Jingkun, HU Xiujiement company of Shanghai).& CHEN Ping(- i) Preparation of hybrid films. PEDOT-PSS dis-persions were mixed by desired amount of PEG with dif-Technical Isitute of Physics and Chemist, Chine Academy of ferent MW (i.e. Mn = 400, 800 and 2000). The mixturesSciences, Beijing 100101, ChinaCorrespondence should be addressed to Chen Ping (e-mail:chenlab@were stirred continuously for 24 h at RT. The hybrid filmsmail.ipc. ac .cn)were then prepared by casting those dispersions on freshlyAbstract By mixing various concentrations of poly (eth-cleaned glass substrates. The coated samples were dried atylene glycol), a series of poly(3,4-ethylenedioxythiophene)-70.( for 24 h. Films thickness was 30 - -50 μum.poly(styrenesulfonate) composite thin films were prepared.(1i) Measurements of electrical conductivity. TheThe electrical conductivity of the PEDOT-PSS/PEG thinelectrical conductivity of the films was measured by thefilmms was measured bv the four-pr:obe method. ExperimentalIfour-probe method at various temperatures.results showed that the inclusion of poly(ethylene glycol)influenced the electrical conductivity of PEDOT-PSS film 2 Results and discussionsignificantly. With the increase of PEG concentrations, theelectrical conductivity sharply increased to reach a maxi-(- i) Effect of concentration and molecular weight ofmum and then slowly decreased down. Furthermore, the PEG on PEDOT-PSS. The mixed dispersions of PE-PEG molecular weight and environment temperature also DOT-PSS and PEG (Mn = 400, 800, 2000) of variousplayed important roles on the electrical conductivity of PE-concentrations were cast on glass substrates. ElectricalDOT-PSS/PEG thin films. A good linear relationship wasconductivity of the films was measured by the four-probefound between In σ nc and T -I/2 within the entire temperaturemethod. Fig. 1 presents the curve of electrical conductiv-range detected.Keywords: PEDOT-PSS, poly(ethylene glycol), electrical conductiv-ity of the above-mentioned hybrid films as a function ofthe concentration of PEG of various molecular weights.ity, hybrid film, four-probe method.The electrical conductivity of PEDOT-PSS thin film in the .DOI: 10.1360/03wb0134absence of PEG was 0.1 S/cm. As shown in Fig. 1, theelectrical conductivity changed significantly after thConducting polymer has been very interestingl.21 af-addition of PEG. Mixed by PEG400, the lowest MW one,ter being discovered due to its potential applications. Poly-where the concentration was below 1.>10-2 mol/L, the(3,4-ethylenedioxythiophene)(PEDOT) has attracted muchelectrical conductivity increased only from 0.1 to 0.24attention in the field of conducting polymer because of itsS/cm. However, with a further increase of the PEG400' shigh electrical conductivity, structural stability and otherconcentration, the electrical conductivity increased shar-predominant property of its doped state. But the intrinsicalply and reached a maximum of 17.7 S/cm, which was twostate of PEDOT has a low extremely electrical conductiv-orders of magnitude higher than the negative sample, at aity and is neither soluble nor fused. Hybrid ofPEG concentration of 4.06. >10-2 mol/L, and then slowlypoly(styrenesulfonate) (PSS) and PEDOT can form aque-decreased down. Similarly， the electrical conductivityous dispersion, and their coated films are highly stable inchanged much for the PEDOT-PSS films after addingair. Meanwhile, the aqueous dispersion is processable, andPEG800, from 0.1 S/cm to 1.7 S/cm when the concentra-the producing material keeps a high electrical conductivityresuting in the promotion of the aplication of PEDOT. tion of PEG was below 1.x10 2mol/L. Whereas, it sharplyBesides the favors described above, researches on theincreased, up to two orders of magnitude higher comparedfactors infecting PEDOT-PSS film electrical conductivityto the film without PEG, i.e. 14.2 S/cm, with the increasecan also help us to solve some of the basic problems and of PEG conc中国煤化工mol/L, and againfactors on the conducting mechanism of conducting poly- fllwed by|YHs noted that finemers. In the present work, PEDOT-PSS/PEG hybrid filmsfilms were ndCN M H Grion of PECG2000were prepared by the mixing method and their elctrical higher than 3.33..- 10-2 mol/L because the molecularconductivity was measured by the four-probe method. weight of PEG2000 was relatively large. Nevertheless, the24月方数据Chinese Science Bulletin Vol. 48 No. 22 November 2003REPORTSelectrical conductivity of the PEDOT-PSS/ PEG2000 energy separation of charge carrier hopping, which result-films increased to 6.5 S/cm within a PEG concentration ed in the increase of the electrical conductivity.interval of (0 - -1.25)- >10-2 mol/L, still being enhanced byone order of magnitude and then rapidly decreased. Fur-thermore, the molecular weight affected distinctly the2.8electrical conductivity. At lower PEG concentration, mix-ing PEG of higher molecular weight resulted in a higher2.66electrical conductivity of the hybrid film while it wasopposite in the higher concentration range. In addition, thePEG concentration needed for the films to get the max2 2.4-electrical conductivity became lower when the molecularweight of PEG increased. And the film mixed by PEG of2.2lower molecular weight had a higher maximum electricalconductivity value.2.0。PEG4000.060.07008I0.0916●PFG800T-1/K-▲PEG2000Fig. 2. Effect of temperature on PEDOT-PSS/PEG conductivity. Con-PEG400 is 7.18 - >10-2 mol/L.3 ConclusionThe addition of PEG affected significantly the elec-trical conductivity of PEDOT-PSS film. And the effect ofmolecular weight of PEG on electrical conductivity pre-sented a regular variation. The electrical conductivity ofPEDOT-PSS/PEG hybrid films reached a maximum with°0.0 2.4.0 6.0 8.0 10.0 12.0the increase of PEG concentration. The environment tem-Concentration/mol:L(X 10~2)perature also played an important role in the electricalFig 1. Effect of PEG concentration, molecular weight on PEDOT-PSSconductivity of PEDOT- PSS/PEG thin films. A goodlinear relationship was found between ln- qc and TI/2conductivity.within the entire temperature range detected. By analysis,(_ i) The relationship of elecrical conductivity ofinclusion of PEG may result in the decrease of effectivePEDOT-PSS/PEG hybrid films and the temperature.energy separation of charge carrier hopping, giving rise toThe electrical conductivity of PEDOT- PSS/PEG hybrid the increase of the electrical conductivity.films was affected greatly by the environment temperature.Acknowledgements The authors gratefully acknowledge the astanceTheir relationship follows a quasi one-dimension variable from Doctor Long Yunze of Institute of Physics, CAS and Doctor Qurange hopping model (1D-VRH)5, which is described asXiaozhong of Institute of Chemistry, CAS.σ Dc(T)=σ sexp[-(TJT)'"],(1ReferencesTo= 8o/ZN(Ep),1. Skotheim, T A. (ed.), Handbook of Conducting Polymers, Newwhere σ pc (T) is electrical conductivity, T is temperatureYork: Marcel Dekker, 1986.and σo is a constant. To can be interpreted as an effctive2. Skotheim, T A.. Elsembaumer, R. L.. Reynolds, J. R. (eds), Hand-book of Conducting Polymer, New York: 2nd edition Marcel Dek-energy separation of charge carrier. Relationship of To andker, 1998 .the localized length, the density of states is shown in (2),3. Francois Tran-Van, Sebastien Garreau,Guy Louarn et al., Fully un-where a is the localized length, and Eris the density ofdoped and soluble oligo(3,4-ethylenedioxythiophene)s: spectro-states at the Fermi level. k, Z are boltzmann' s constant andscopic study and electrochemical characterization, Journal of Mate-the number of the neighboringest respectively. It is ob-rial Chemistry, 2001, 11: 1378 - -1382.tained by eq. (1):4. Lefebvre, M, Qi, Z, Rana, D. et al, Chemical synthesis, charac-lnσ Dc(T)=- (T/T)'2 + lnσ o(3terization and electrochemical studies of poly(3,4- ethylenedi-oxythiophene)/poly(styrene-4-sulfonate) composites， ChemicalTo, an effective energy separation of charge carrier, can bMaterialscalculated by the slope of Inσ Dc(T). The value of To of the5. Kim,J. Y,中国煤化工EIncement of electricalPEDOT-PSS/PEG hybrid film was calculated as ~745 KconductivitYHC N M H Gene/polystyene- 4-from Fig. 2, which was much lower compared to that ofsulfonate) by a change ot solvents, synthetc Metals, 2002, 126:PEDOT-PSS film (Tr=~1700 K!). The results inferred311 ~ 316.that the inclusion of PEG could decrease the effective(Received July 24, 2003; accepted September 9, 2003)Ch月9数ience Bu/etin Vol. 48 No. 22 November 20032445 .