Effective decoupling of seebeck coefficient and the electrical conductivity through isovalent substitution of erbium in bismuth selenide thermoelectric material

Recognizing high thermoelectric performance in semiconducting materials is a challenging task. This is because the Seebeck coefficient and electrical conductivity which constitute the thermoelectric power factor are unfavourably coupled. This means decoupling the transport properties of thermoelectric materials to enhance the power factor without compromising the thermal conductivity is essential. Herein we report that the substitution of erbium (Er) within bismuth selenide (Bi₂Se₃) results in a simultaneous enhancement in Seebeck coefficient and electrical conductivity via effective mass and Fermi energy optimization. The Er-Substitution in Bi₂Se₃ does not only promote a simultaneous increase in Seebeck coefficient and electrical conductivity but also decreases the thermal conductivity through an enhancement in phonon scattering. Consequently, the optimum composition is found for the Bi_1·85Er_0·15Se₃ sample instigating that, minimal substitution amount is required to optimize the thermoelectric performance. Our numerical calculation also shows that Er substitution alters the Fermi energy of the Bi₂Se₃ TE materials, thereby enhancing the effective mass. Through Raman and XPS characterization, we also elucidate that Er substitution does not change the chemical structure and chemical bonding of the pristine material appreciably. It thus leads to improvement in the Seebeck coefficient and electrical conductivity via effective mass optimization. This unique work presents a facile, scalable, cost-effective, and controllable synthesis of nanostructured Bi₂Se₃ toward realizing high-performance thermoelectric devices.