In this work, PEDOT:PSS used as hole transport layer of electorde in OLED, OTFT, OSC, Fuel Cell application, was incorporated with various inorganic nanoparticles for tuning its properties. For this purpose, insulating oxide, semiconducting oxide, sem...
In this work, PEDOT:PSS used as hole transport layer of electorde in OLED, OTFT, OSC, Fuel Cell application, was incorporated with various inorganic nanoparticles for tuning its properties. For this purpose, insulating oxide, semiconducting oxide, semiconducting compound, and metal nanoparticles were adopted and rexfluxed with PEDOT:PSS solution. Change of Bonding states, valence band structure, surface morphology, and so on of inorganic NPs-PEDOT:PSS hybrid films were 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.
Formation of good interface with active layes enable superior electrical properties in organic devices although it show lower conductivity of 0.5 - 500 s/cm than ITO anode material. PEDOT has excellent transparency in the visible region, good electrical conductivity, and environmental stability. Unfortunately PEDOT, like most conducting polymers, is infusible and insoluble and therefore difficult to process in a thin-film form or in other shapes. Lack of processability has been a major impediment to the commercial acceptance of this polymer. A water dispersion of PEDOT doped with poly(styrenesulfonate) (PSS) is available. Properties of PEDOT:PSS, such as conductivity and work function, can be modified by the incorporation with nanoparticles. Tuning of electrostatic force, doping level, and properties of nanoparticle itself. are possible.
First, 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.
SiO2 is insulating oxide with little surface defect unlike with SnO2 nanoparticle. 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. Moreover, co-doping with other nanoparticles is also preferable.
With high dielectric constant and dipole moment of CdSe nanocrystal induced segregation of PEDOT and PSS during solution refluxing. Workfunction of CdSe-PEDOT:PSS similar with undoped PEDOT and semiconducting state with higher band gap than pristine PEDOT:PSS were observed. Metallic properties of CdSe-PEDOT:PSS were recovered with increase annealing temperature. Strong steric effect by surface pyridine affect the resulting poor packing density at low annealing temperature and vice versa at high annealing temperature of 230℃. Value of IP calculated was 0.3 eV higher that of pristine PEDOT:PSS and suggesting localization of electron on the surface of CdSe nanocrystal.
In the synthesis of metallic 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.
One pot synthesis of metal nanoparticles-PEDOT:PSS hybrid films was conducted to remove the effect of alkali metal ion, sodium. AgNO3 and H2PtCl6 were directly added in the PEDOT:PSS water solution. Ag nanoparticles with 10- 30 nm size were synthesized in PEDOT:PSS and showed bulk metallic effects. Lowered workfunction was measured by the bond formation with PSS instead of doping PEDOT. In the valence band spectra, difference between HOMO edge and Fermi energy level increased and the reason why is the electron-donation from Ag nanopartricles to PEDOT chain.
With high workfunction metal, Pt, characteristic of M- δ+ lead to doping of PEDOT. During formation of Pt nanoparticles from Pt salt ion, Pt ions, and PtOH, PEDOT:PSS and metallic ions coagulated to form large agglomeration. The size of synthesized Pt nanoparticles is in the range of 3 - 5nm. Control of refluxing time and temperatre enabled us to obtain monodispersed or fractal structure of Pt nanoparticles and prevent bing agglomerated metal nanoparticles. Work function of Pt-PEDOT:PSS hybrid films were increased to 5.45 ev, in that case, work function of pristine PEDOT:PSS was calculated to 4.95 eV. Pt nanoparticles played a role of PSS dopant and increased dopinf level of PEDOT:PSS. HOMO edge energy was also shift to fermil energy level.
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