Conductivity and Thermoelectric Properties of Doped Polymers

Conducting polymers combine the mechanical flexibility and processability of plastics with electronic transport characteristics more typical of inorganic semiconductors. Through the introduction of dopants—small redox‐active molecules or ion pairs—it is possible to tune carrier concentration and thereby electrical conductivity by several orders of magnitude. Doped polymers exhibit a balance of ionic and electronic conduction, enabling mixed‐conduction phenomena that underpin applications in bioelectronics, neuromorphic devices and flexible thermoelectrics. Thermoelectric performance is gauged by the Seebeck coefficient, electrical conductivity and thermal conductivity, which together define the power factor and the dimensionless figure of merit ZT. Progress in this field hinges on controlling dopant chemistry, counterion interactions and polymer morphology to minimise energetic and structural disorder, enhance carrier mobility and maintain thermal stability. Recent advances have revealed non‐equilibrium transport regimes, the critical role of non‐covalent counterion docking and the selective formation of charge species in ordered versus disordered domains. These insights offer pathways to optimise both conductivity and thermoelectric output in next‐generation organic materials.

Research from Nature Portfolio

Recent studies have shown that in mixed ionic–electronic conductors it is possible to access non‐equilibrium transport regimes by combining electrochemical gating with field‐effect control. By tuning the injection of electrons or holes at fixed doping levels, researchers have observed the emergence of a frozen, soft Coulomb gap and correlated transport signatures reflecting strong electron–ion coupling. These findings suggest new strategies for enhancing conductivity by exploiting trapped charge states and slow counterion equilibration. In parallel, computational screening of counterions has identified optimal species whose non‐covalent interactions with the polymer backbone dramatically reduce counterion‐induced energetic disorder. By docking selected ionic species at specific binding sites, it has been possible to lower energetic disorder below that of the pristine polymer, achieve n‐doped conductivities exceeding 200 S cm⁻¹ and boost the thermoelectric power factor by eight‐fold. This work underscores the importance of tailoring counterion chemistry to attain both high carrier mobility and thermoelectric efficiency.

Conductivity and Thermoelectric Properties of Doped Polymers publication trend

The graph below shows the total number of articles in conductivity and thermoelectric properties of doped polymers across all publications each year (not limited to Nature Index journals).

Technical terms

Electrical conductivity: A measure of a material’s ability to transport electrical charge per unit length and cross‐section under an applied potential.

Seebeck coefficient: The voltage generated per unit temperature difference across a material, indicative of its thermoelectric voltage response.

Power factor: The product of the square of the Seebeck coefficient and the electrical conductivity, reflecting the electrical contribution to thermoelectric efficiency.

Polaron and bipolaron: Quasi‐particles formed by a charge carrier (polaron) or two carriers (bipolaron) coupled to local polymer chain distortions.

Energetic disorder: Variations in the local energy landscape of a semiconductor that hinder uniform charge transport and reduce mobility.

Ion‐exchange doping: A technique that separates redox and compensating‐ion steps by exchanging ions between a dopant solution and the polymer matrix to achieve high carrier densities.

References

1. Non-equilibrium transport in polymer mixed ionic–electronic conductors at ultrahigh charge densities. Nature Materials (2024).
2. Counterion docking: a general approach to reducing energetic disorder in doped polymeric semiconductors. Nature Communications (2024).
3. Electrochemical Doping in Ordered and Disordered Domains of Organic Mixed Ionic–Electronic Conductors. Advanced Materials (2023).
4. Observation of Weak Counterion Size Dependence of Thermoelectric Transport in Ion Exchange Doped Conducting Polymers Across a Wide Range of Conductivities. Advanced Energy Materials (2023).
5. A Universal, Highly Stable Dopant System for Organic Semiconductors Based on Lewis-Paired Dopant Complexes. ACS Energy Letters (2024).