Understanding the Microscopic Origin of the Contact Resistance at the Polymer-Electrode Interface

Area of Science:

• Organic electronics
• Materials science
• Solid-state physics

Background:

• Contact resistance (RC) in organic devices arises from energy level mismatches between electrodes and organic semiconductors (OSCs).
• Microscopic factors influencing charge transfer at these interfaces remain incompletely understood.

Purpose of the Study:

• To investigate the microscopic origins of contact resistance in organic field-effect transistors (OFETs).
• To correlate charge transfer rates with measured contact resistance across various OSCs and electrode materials.

Main Methods:

• Fabrication of OFETs using diverse OSCs (PTB7, PCDTBT, PTB7-Th) and electrodes (MoO3, Au, Ag).
• Measurement of contact resistance (RC) for fabricated devices.
• First-principles computations using the projector operator diabatization method to analyze interface electronic structure and couplings.

Main Results:

• PTB7-Th based devices consistently showed the lowest contact resistance, irrespective of the electrode material.
• First-principles calculations identified energy level alignment and electronic coupling between OSC highest occupied molecular orbitals (HOMOs) and electrode states as key factors influencing RC.
• Calculated charge transfer rates demonstrated a strong correlation with observed contact resistance trends.

Conclusions:

• Device contact resistance is fundamentally governed by the feasibility of charge transfer at the OSC-electrode interface.
• Optimizing energy levels and electronic coupling between OSCs and electrodes is crucial for minimizing contact resistance in organic electronic devices.