Solution-processed organic thermoelectric materials exhibiting doping-concentration-dependent polarity.

Area of Science:

• Materials Science
• Organic Electronics
• Thermoelectrics

Background:

• Conducting polymer-based organic thermoelectric generators (OTEGs) show promise for high performance via controlled redox levels.
• Solution processing is crucial for OTEG module fabrication, but limited soluble n-type materials hinder complementary p- and n-type structures.
• Low electrical conductivity (σ) in n-type materials is a significant challenge for OTEG performance.

Purpose of the Study:

• To investigate poly(pyridinium phenylene) (P(PymPh)) as a soluble n-type semiconductor for solution-processed OTEGs.
• To explore the carrier density control and doping mechanism of P(PymPh) using a solution-based chemical doping process.
• To demonstrate the potential for polarity switching in organic thermoelectric materials.

Main Methods:

• Chemical doping of P(PymPh) using sodium naphthalenide as a reductant.
• Characterization of electronic structures and doping mechanisms via UV-Vis-IR absorption, ultraviolet photoelectron spectroscopy, and X-ray photoelectron spectroscopy.
• Fabrication and performance evaluation of OTEG modules with varying dopant concentrations.

Main Results:

• Achieved a maximum n-type power factor of 0.81 μW m⁻¹ K⁻² with high electrical conductivity (σ).
• Demonstrated a switch from n-type to p-type thermoelectric operation by increasing reductant (dopant) concentration.
• Explored the electronic structures and doping mechanism of P(PymPh) through spectroscopic analysis.

Conclusions:

• P(PymPh) shows potential as a versatile n-type semiconductor for organic thermoelectric generators.
• The ability to switch polarity by adjusting dopant concentration offers a novel route for simplified fabrication of complementary organic layers.
• This study addresses the scarcity of soluble n-type materials and the challenge of low σ in organic thermoelectrics.