Counterion

Electrical resistivity and conductivity

Engineering

Chemical physics

Materials science

Thermal conductivity

Dopant

Organic semiconductor

Thermoelectric effect

Semiconductor

Chemical engineering

Seebeck coefficient

Thermoelectric materials

Thermodynamics

Physics

Nanotechnology

Organic chemistry

Doping

Composite material

Chemistry

Optoelectronics

Electrical engineering

Engineering physics

Advanced Energy Materials

Molecular doping is a powerful method to fine‐tune the thermoelectric properties of organic semiconductors, in particular to impart the requisite electrical conductivity. The incorporation of molecular dopants can, however, perturb the microstructure of semicrystalline organic semiconductors, which complicates the development of a detailed understanding of structure–property relationships. To better understand how the doping pathway and the resulting dopant counterion influence the thermoelectric performance and transport properties, a new dimer dopant, (N‐DMBI) 2 , is developed. Subsequently, FBDPPV is then n‐doped with dimer dopants (N‐DMBI) 2 , (RuCp*mes) 2 , and the hydride‐donor dopant N‐DMBI‐H. By comparing the UV–vis–NIR absorption spectra and morphological characteristics of the doped polymers, it is found that not only the doping mechanism, but also the shape of the counterion strongly influence the thermoelectric properties and transport characteristics. (N‐DMBI) 2 , which is a direct electron‐donating dopant with a comparatively small, relatively planar counterion, gives the best power factor among the three systems studied here. Additionally, temperature‐dependent conductivity and Seebeck coefficient measurements differ between the three dopants with (N‐DMBI) 2 yielding the best thermoelectric properties. The results of this study of dopant effects on thermoelectric properties provide insight into guidelines for future organic thermoelectrics.

Understanding the Effects of Molecular Dopant on n‐Type Organic Thermoelectric Properties