Work function modification of PEDOT:PSS by mixing with barium acetylacetonate

Area of Science:

• Materials Science
• Organic Electronics
• Surface Chemistry

Background:

• Poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT:PSS) is a widely used hole injection/extraction material in organic electronics.
• Modifying the work function of PEDOT:PSS is crucial for optimizing electron injection/extraction capabilities.

Purpose of the Study:

• To investigate the n-doping of PEDOT:PSS using barium acetylacetonate (Ba(acac)2).
• To determine if Ba(acac)2 can alter the work function of PEDOT:PSS for improved electron transport.
• To explore the potential of modified PEDOT:PSS as an electron injection/extraction layer.

Main Methods:

• Molecular dynamics simulations to predict interactions between barium cations and PEDOT:PSS.
• Chemical treatment with Ba(acac)2 followed by filtration.
• X-ray photoelectron spectroscopy (XPS) to analyze chemical state changes.
• Work function measurements of spin-coated films on indium tin oxide (ITO).
• Device testing using an electron transporting layer.

Main Results:

• Molecular dynamics simulations indicated favorable interactions between barium and PEDOT:PSS components.
• High doping concentrations led to PEDOT precipitation and a clear solution after filtration.
• XPS confirmed the ionization of polystyrene sulfonic acid to barium polystyrene sulfonate (Ba-PSS).
• Spin-coating resulted in a significantly lowered work function, down to 3.6 eV.
• An interfacial dipole of 1.37 eV was observed at the ITO/Ba-PSS interface.

Conclusions:

• Barium acetylacetonate effectively n-dopes PEDOT:PSS, leading to barium polystyrene sulfonate.
• The modified material exhibits a substantially reduced work function suitable for electron injection.
• The formation of an interfacial dipole at the ITO interface is responsible for the work function modulation.