Dopant Induced Interchain Interactions Enhance Polythiophene Electrical Conductivity at Low Dopant Concentrations

Area of Science:

• Materials Science
• Organic Electronics
• Semiconductor Physics

Background:

• Achieving high electrical conductivity in organic semiconductors at low dopant levels is crucial for solution-processed optoelectronics.
• Maintaining film morphology during doping is a significant challenge for device performance.

Purpose of the Study:

• To investigate the effect of tetracyanoquinodimethane (TCNQ)-based dopants on the electrical conductivity and morphology of poly(3-hexylthiophene) (P3HT) films.
• To understand the factors influencing charge transport beyond dopant electron affinity.

Main Methods:

• Solution processing of poly(3-hexylthiophene) (P3HT) films.
• Doping with tetracyanoquinodimethane (TCNQ) and F4TCNQ.
• Electrical conductivity measurements.
• Two-dimensional electronic spectroscopy.
• Pump-probe spectroscopy.

Main Results:

• TCNQ dopants increased P3HT conductivity to over 0.01 S/cm at 3 wt % concentration, a two-order-of-magnitude improvement.
• Dopant performance was comparable to F4TCNQ, indicating transport is influenced by structural disorder and Coulomb interactions, not just electron affinity.
• Spectroscopic analysis revealed uniform morphology, no preferential doping in crystalline domains, and rapid polaron pair formation.
• Evidence of polaron-induced backbone planarization enhancing charge delocalization and coupling.

Conclusions:

• TCNQ-based dopants effectively enhance conductivity in P3HT films at low concentrations while preserving morphology.
• Charge transport is a complex interplay of dopant properties, structural disorder, and electronic interactions.
• The findings provide insights into optimizing organic semiconductor performance for optoelectronic applications.