Prof. Hyung-Ho Park, Department of Materials Science and Engineering, Yonsei University, Korea

Speech Title:Nanoparticles incorporation effect on PEDOT: PSS polymer films

. Abstract:In this work, PEDOT:PSS was incorporated with various inorganic nanoparticles such as insulating oxide, semiconducting oxide, and metal nanoparticles. Change of bonding states, valence band structure, surface morphology, and so on of inorganic NPs-PEDOT:PSS hybrid films by the incorporation with nanoparticleswere investigated by AFM, XPS, anlysis tools in Pohang acceleration laboratory. Comparative study with the properties of pristine PEDOT:PSS enabled us to confirm the effect of nanoparticles on the properties of PEDOT:PSS and resultant properties of PEDOT:PSS hybrid material.

SiO2 is insulating oxide with little surface defect. Steric effect, dielectric constant, and surface -OH bonds must be considered. Weak Coulombic bond and increase doping level can be obtained by surface -OH and steric effect. Difference between HOMO edge and fermi level also inferred doping of PEDOT ring by surface -OH. The increased conductivity after annealing of SiO2-PEDOT:PSS is accompanied by a lowering of the work function. Precise control of properties of PEDOT:PSS, such as conductivity, work function, and IP, is possible by SiO2 nanoparticle incorporation of its surface -OH and steric effect.

SnO2 nanoparticle with 3.5 - 4 nm size was synthesized and refluxed in PEDOT:PSS. Fermi level of n-type SnO2 is located upper side of conductiong band. SnO2 nanopartices is high dielectric material and its oxygen deficient surface was surrounded by -OH radicals. On the refluxing solution, SnO2 nanoparticle give physical energy to PEDOT:PSS and hindered bonding between PEDOT:PSS similar to dielectric DMSO solvent, which induced segregation of PEDOT and PSS and resulting rearrangement of PEDOT and PSS chains during annealing. Packing density increassed by coil to linear or extended coil conformation by steric effect. Conductivity was enhanced by compaction of PEDOT chain and conductive SnO2. Bond formation between PEDOT and SnO2 nanoparticles by weak Coulomic force between surface OH- and PEDOT ring. Increase of workfunction and HOMO energy level from secondary electron emission spectra and valence band spectra. Hole in VBm of SnO2 nanoparticles migrate to the PEDOT:PSS and electron of PEDOT can hop to the CBM of SnO2 nanoparticles.

In the synthesis of Ag nanoparticles, sodium ions are abundant in the nanoparticle solution because of using reducing agent and surface capping molecules, such as NaBH4, sodium dodecyl sulfonate, and sodiym citrate. Sodium ion induced PSS:Na bond with anionic dopant PSS and decrease electrostatic bonding site of PEDOT and PSS. In case of lower content Ag nanoparticle, effects of sodium ion were pronounced, decreased workfunction of PEDOT:PSS, and changed metallic band structure to semiconducting state. However, with increasing Ag nanoparticle content, metallic state of PEDOT:PSS was recovered even if high content of sodium from XPS measurement. After the synthesis of metal nanoparticle, elimination of alkali metal ion is indispensible for compostie formation with conjugate polymers.

Various inorganic nanoparticles were used to form PEDOT:PSS hybrid films. Inorganic nanoparticles can modify the properties of PEDOT:PSS, such as surface morphology, workfunction, HOMO level, and so on. These results can be adopted in the region of electronic application and applied to other kinds of polymeric nanocomposite materials for modification of electronic properties.