Morphology Determines Conductivity and Seebeck Coefficient in Conjugated Polymer Blends

Area of Science:

• Materials Science
• Organic Electronics
• Solid-State Physics

Background:

• All-polymer blend systems are crucial for organic electronics.
• Understanding nanoscale morphology's impact on thermoelectric properties is key for device optimization.

Purpose of the Study:

• Investigate the influence of nanoscale morphology on conductivity and Seebeck coefficient in p-type doped all-polymer blends.
• Correlate morphological differences with charge transport mechanisms.

Main Methods:

• Fabrication and characterization of P3HT:PTB7 and P3HT:PCPDTBT polymer blends with varying morphologies.
• Measurement of Seebeck coefficient (S) and conductivity (σ).
• Analysis using the variable range hopping (VRH) model and atomistic kinetic Monte Carlo simulations.

Main Results:

• Phase-separated P3HT:PTB7 blends achieved a peak Seebeck coefficient (S ∼ 1100 μV/K) and lower conductivity (σ ∼ 3 × 10⁻³ S/cm).
• Well-mixed blends (P3HT:PTB7 with DIO, P3HT:PCPDTBT) exhibited constant S (∼ 140 μV/K) and higher conductivity (σ ∼ 1 S/cm).
• VRH model successfully explained the observed trends, attributing differences to percolation pathways involving host and guest sites.

Conclusions:

• Nanoscale morphology dictates charge transport pathways and thermoelectric performance in polymer blends.
• Energetic traps within the percolation pathway significantly influence the Seebeck coefficient.
• Controlled phase separation is a viable strategy to enhance the Seebeck coefficient in p-type all-polymer thermoelectric materials.