Grain Boundary-Induced Work Function Heterogeneity in Yb₂O₃ Thin Films on ITO.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Surface Science

Background:

• Ytterbium oxide (Yb2O3) enhances electron injection in organic light-emitting diodes and photovoltaics.
• The work function tuning and heterogeneity of Yb2O3 remain poorly understood.
• Understanding these properties is crucial for optimizing device performance.

Purpose of the Study:

• To systematically investigate the thickness-dependent work function of Yb2O3.
• To explore the heterogeneity of the work function at the nanoscale.
• To elucidate the role of Yb2O3 in electron injection mechanisms.

Main Methods:

• Thermal evaporation of Yb2O3 films on indium tin oxide (ITO).
• Pulsed Force Kelvin Probe Force Microscopy (PF-KPFM) for work function measurements.
• High-resolution PF-KPFM mapping to analyze surface heterogeneity.

Main Results:

• Work function of Yb2O3 decreases with increasing film thickness.
• An interfacial dipole formation at the Yb2O3/ITO interface is responsible for the work function reduction.
• PF-KPFM revealed significant work function heterogeneity, particularly at grain boundaries.

Conclusions:

• The work function of Yb2O3 is tunable via film thickness.
• Interfacial dipole formation plays a key role in modifying the work function.
• Lateral variations in work function may facilitate a cascade mechanism for electron transport.
• Electron transport in electron injection layers might involve multistep pathways.