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

The DC conductivity (σ_DC) 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 [σ_DC(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, σ_DC(RT) of the samples increases from ∼0.8 to ∼80 S/cm. The temperature dependence of DC conductivity [σ_DC(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 (σ_DC ∝ T^β). 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 σ_DC of the PEDOT/PSS systems.