Quantifying the Extent of Contact Doping at the Interface between High Work Function Electrical Contacts and...

Area of Science:

• Materials Science
• Organic Electronics
• Surface Science

Background:

• Regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) is a key organic semiconductor.
• Understanding charge transfer at interfaces is crucial for device performance.
• Oxidation of P3HT by high work function contacts affects electronic properties.

Purpose of the Study:

• To characterize oxidized P3HT resulting from electronic equilibration with electrical contacts.
• To quantify the extent of charge transfer and oxidation at the P3HT/contact interface.
• To develop advanced spectroscopic methods for interface analysis in organic electronic devices.

Main Methods:

• High-resolution X-ray (XPS) and ultraviolet (UPS) photoelectron spectroscopy (PES).
• Analysis of thiophene sulfur 2p core-level spectra.
• Comparison with electrochemically oxidized P3HT standards.
• Angle-resolved XPS (ARXPS) for depth profiling.

Main Results:

• Photoemission signals from sulfur atoms elucidate charge transfer products.
• Quantified oxidation: ~20% of thiophene units in the first monolayer are oxidized.
• Oxidized P3HT species are confirmed near contacts with work functions > 4 eV.
• ARXPS distinguishes interface and bulk regions in P3HT/PCBM blends.

Conclusions:

• PES provides a unique method to characterize P3HT oxidation due to Fermi-level equilibration.
• The extent of contact doping reaction is quantifiable.
• Spectroscopic methods can characterize both the interface and bulk of organic semiconductors in situ.