Enhancement of electrical conductivity of poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) by a change of solvents
Introduction
Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(4-styrenesulfonate) (PSS) has attracted much attention during the last decade [1], [2]. PEDOT/PSS with H2O as a pristine solvent is optically transparent, well spin-coated, and a hole transport material [3], [4], [5]. The PEDOT/PSS has been widely used as an antistatic coating material, as electrodes for capacitors or photodiodes, and as a hole transport layer of organic LED [6], [7]. The increase of conductivity of the PEDOT/PSS sample provides various uses of the systems such as an electromagnetic radiation shielding and a better electrical transport layer. Yamato et al. [8] reported the effect of various electrolyte anions on physical and chemical properties of electrochemically synthesized PEDOT films. Cao et al. [9] studied that DC conductivity (σDC) of polyaniline (PAN) films was dependent on the chemical nature of both counter-ions and solvents. MacDiarmid and Epstein [10] reported that a change of solvent for doped PAN samples induced the change of σDC and the molecular conformation from ‘compact coil’ to ‘expanded coil’, so-called the ‘secondary doping effect’.
In this study, we report the effects of organic solvents on charge transport properties for the PEDOT/PSS systems. We observe the increase of room temperature DC conductivity [σDC(RT)] of the systems from ∼0.8 to ∼80 S/cm by the change of solvent. The results of thermoelectric power, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) experiments are presented.
Section snippets
Experiment
The PEDOT/PSS (Baytron P) was purchased from Bayer AG. Baytron P was an aqueous dispersion of the conductive polymer, PEDOT/PSS. The weight ratio of PEDOT to PSS was 1:1.6, and the mixture was diluted with H2O. Baytron P (PEDOT/PSS) and the organic solvent were mixed by the volume ratio of 3:1 (PEDOT/PSS:organic solvent). The solvents used were dimethyl sulfoxide (DMSO), N,N-dimethyl formamide (DMF), tetrahydrofuran (THF), H2O (as pristine solvent). The mixed solution of PEDOT/PSS and organic
Results and discussion
Table 1 shows σDC(RT) of the PEDOT/PSS films with various solvents (H2O, THF, DMF, and DMSO). The σDC(RT) of the PEDOT/PSS films prepared from H2O, THF, DMF, and DMSO solvents is ∼0.8, ∼4.0, ∼30, and ∼80 S/cm, respectively. PEDOT/PSS with DMSO exhibits the highest σDC(RT). We control σDC through the solvent.
Fig. 1 compares σDC(T) of the PEDOT/PSS samples. The σDC(T) of the PEDOT/PSS with H2O sample follows a quasi one-dimensional (1D) variable range hopping (VRH) model [12] as shown in the inset
Conclusion
We observe the increase of σDC in the PEDOT/PSS systems through the change of solvent from ∼0.8 to ∼80 S/cm. The temperature dependence of W(T) shows that the PEDOT/PSS system approaches the critical regime when organic solvents (THF, DMF, and DMSO) are used. From XRD and the absorbance experiments, the polymer chain conformation of the samples does not changed by the solvent used. The doping concentration of the systems with various solvents is almost the same, which is observed by EPR and XPS
Acknowledgements
This work was supported in part by a Korea University Grant, 2001.
References (19)
- et al.
Polymer
(1994) - et al.
Synth. Met.
(1999) - et al.
Synth. Met.
(1997) - et al.
Synth. Met.
(1999) - et al.
Synth. Met.
(1999) - et al.
Synth. Met.
(1996) - et al.
Synth. Met.
(1995) - et al.
Synth. Met.
(1994) - et al.
Synth. Met.
(1997)