Electrical conductivity enhancement of spin‐coated PEDOT:PSS thin film via dipping method in low concentration aqueous DMSO

Abstract

The electrical conductivity of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was enhanced by dipping the thin films prepared by spin coating technique in an aqueous DMSO solution. The low concentration range of DMSO in water between 0-5 vol % was studied in comparison with pure water and pure DMSO. It was found that the electrical conductivity dramatically increased as increasing the concentration of DMSO and reached the constant value of 350 S cm-1 at 2 vol % of aqueous DMSO solution. This could be explained by the conformational change of PEDOT chains from the coil structure to the linear or expanded coil structure as confirmed by Raman spectra. Further, white patches were obviously noticed on the surface of the films dipped in pure DMSO, indicating the phase separation of conductive PEDOT grains and associated PSS. The sulfur element of the dipped film surface was investigated by XPS. The XPS S2p core-level spectra displayed that the unassociated PSS was considerably removed from the surface of PEDOT:PSS films dipped in pure water and 2 vol % of aqueous DMSO solution, indicating that the presence of water in the solvents is important to prominently promote the washing effect. Finally, UV-Vis spectra revealed the improved transparency of the films probably owing to the decreased film thickness

Electrical properties of nitric acid and DMSO treated PEDOT:PSS/n‐Si hybrid heterostructures for optoelectronic applications

“…Thicknesses of PEDOT:PSS layers are found to be 200 nm for S1, 130 nm for S2, 150 nm for S3, 185 nm for S4, and 95 nm for S5, respectively. The reduced thickness of sample (S2) is attributed to the washing‐away of unassociated PSS–rich layer on the film surface upon dipping . For samples S3 and S5, PSS‐rich domains disappear post HNO 3 vapor treatment which accounts for the reduced thickness.…”

“…The increase of PEDOT limits the amount of PSS on the surface. Here the addition of co‐solvent leads to rearrangement of PSS chains and also stabilizes them, resulting in reduced defect density at the interface and hence better device performance . In the absence of any co‐solvent, PSS matrix chains tend to surround PEDOT nanocrystals and a high content of PSS chains provide poor Ohmic contact between the top electrode and grain boundaries reducing the carrier collection and hence can reduce the efficiency of the device.…”

“…Surface morphology and root mean square (RMS) roughness were recorded by noncontact mode AFM (as shown in Figure ) and tabulated in Table . The roughness of PEDOT:PSS layers in both S2 and S4 are high as compared to sample S1, as a result of an increase in the PEDOT content and phase separation upon DMSO addition . The appearance of such a surface morphology could be explained as follows: the spin‐coated PEDOT:PSS film is generally composed of PEDOT:PSS grains, with a hydrophobic and highly conductive PEDOT‐rich core and a hydrophilic insulating PSS‐rich shell.…”

“…The percentage transmittance observed were 85 (S2), 83 (S3), 87 (S4), and 90 (S5), respectively. The percentage of transmittance increases nominally for treated PEDOT:PSS because the PSS top layer is washed away in the PEDOT:PSS film dipped with DMSO and PEDOT:PSS layer treated with HNO 3 vapor . A slightly higher transmittance was observed with lower thickness of HNO 3 treated PEDOT:PSS mixed with DMSO (S5).…”

“…In most of these applications, ITO (indium doped tin oxide) is used as the transparent material. However, new transparent materials such as conducting polymer, graphene, and carbon nanotubes have been introduced recently for replacing ITO and to overcome its drawbacks such as high mechanical brittleness, poor adhesion to organic and polymeric materials, and so forth . Organic/inorganic hybrid heterostructures have gained good popularity among materials for photovoltaic device fabrication.…”