Microscopic Origin of Charge Transfer at the Organic Semiconductor/MoO₃ Hybrid Interface

Area of Science:

• Materials Science
• Surface Science
• Organic Electronics

Background:

• Molybdenum trioxide (MoO3) is crucial for organic electronic devices, improving hole injection.
• The precise mechanisms of charge transfer at MoO3/organic interfaces are not fully understood.
• Understanding these mechanisms is key to optimizing device performance.

Purpose of the Study:

• To investigate the microscopic origins of charge transfer between 2H-phthalocyanine (2H-Pc) and ultrathin MoO3 films.
• To explore how adsorption geometry influences charge transfer and electronic structure.
• To provide atomically resolved insights into hybrid organic-inorganic interfaces.

Main Methods:

• Utilized scanning tunneling microscopy/spectroscopy (STM/STS).
• Employed X-ray photoemission spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS).
• Combined experimental data with density functional theory (DFT) calculations.

Main Results:

• Observed clear evidence of integer charge transfer from 2H-Pc molecules to the MoO3 substrate.
• Found that both upright and flat adsorption geometries lead to positively charged molecules.
• Identified distinct SOMO-SUMO gaps (0.4 eV for upright, 1.5 eV for flat) dependent on molecular orientation and screening.

Conclusions:

• Adsorption geometry and local dielectric environment significantly impact charge transfer and electronic structure at hybrid interfaces.
• Atomically resolved insights into charge transfer mechanisms were achieved.
• Findings contribute to the fundamental understanding of MoO3/organic semiconductor interactions for device engineering.