Enhancement of electrical conductivity of poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) by a change of solvents

The DC conductivity (σDC) of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(4-styrenesulfonate) (PSS) with various organic solvents was measured. The solvents used were dimethyl sulfoxide (DMSO), N,N-dimethyl formamide (DMF), tetrahydrofuran (THF), and H2O (as pristine solvent). Room temperature DC conductivity [σDC(RT)] of a free standing film of PEDOT/PSS with H2O was measured to be ∼0.8 S/cm. Through a change of solvents used, σDC(RT) of the samples increases from ∼0.8 to ∼80 S/cm. The temperature dependence of DC conductivity [σDC(T)] of PEDOT/PSS with H2O followed a quasi one-dimensional variable range hopping model, while that of PEDOT/PSS prepared from DMSO, DMF, and THF followed a power law (σDC ∝ Tβ). From X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) experiments, the doping concentration of the systems with different solvents was approximately the same. We analyzed that the screening effect of the solvent plays an important role for the variation of σDC of the PEDOT/PSS systems.