Effect of Regiochemistry on Doping and Thermoelectric Properties of n-Doped Fullerene Derivatives

In recent years, fullerene derivatives have been shown to be a promising candidate for n-type organic thermoelectrics. Adequate tailoring of the solubilizing side chains has proven to be a successful strategy to enhance the performance of these materials. In this work, three different regioisomers of a fullerene derivative are synthesized with two polar diethylene glycol chains. It is shown how small changes in the chemical design alter the assembly properties of the materials, affecting the electronic transport, miscibility with the dopant, and the dielectric properties. It is found that an intermediate crystallinity enables good miscibility, high dielectric constant, and moderate electronic mobility, resulting in a conductivity of 7.7 S cm⁻¹ and a power factor of 35 µW m⁻¹ K⁻², among the highest reported for n-doped molecular semiconductors.