Percolation dependent conducting behavior of poly (3,4-ethylenedioxythiophene): Poly (styrenesulfonate) in the presence of cationic polyelectrolyte

Conductivity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films is highly modified in the presence of cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC). In-plane electrical conductivity of the thin films of PEDOT:PSS and PDADMAC complex (designated as PED*PDA) are measured for one to five layers, i.e., (PED*PDA)₁ to (PED*PDA)₅ films prepared by spin-coating method and compared with the pristine PEDOT:PSS films. In addition, PDADMAC and PEDOT:PSS is spin coated on each other to form a bilayer unit (designated as PDA/PED) and one to five layers of such PDA/PED unit, i.e., (PDA/PED)₁ to (PDA/PED)₅ films are formed by alternate deposition and the conductivity is compared with the complex films. In-plane conductivity of PED*PDA is drastically higher than the pristine PEDOT:PSS and is nearly independent of the layer number, i.e., thickness of the film. However, for PDA/PED films, behavior of conductivity is different in comparison with that of the complex films as the conductivity is found to increase for (PDA/PED)₁ to (PDA/PED)₂ and then decreases from (PDA/PED)₃ to (PDA/PED)₅ respectively. With the increase of the applying voltage, the linear nature of I-V curves remain unchanged. The structure, morphology and mechanism of conductivity enhancement are investigated through various characterization techniques. The strong electrostatic attachment between anionic PSS part of PEDOT:PSS and cationic PDADMAC is responsible for the drastic enhancement of conductivity as the percolation pathway enhances.