AbstractThe single crystals of the ternary system based on Bi2‐xTlxSe3 (nominaly x = 0.0‐0.1) were prepared using the Bridgman technique. Samples with varying content of Tl were characterized by the measurement of lattice parameters, electrical conductivity σ⊥c , Hall coefficient RH (B∥c), and Seebeck coefficient S (ΔT ⊥c). The measurements indicate that by incorporating Tl in Bi2Se3 one lowers the concentration of free electrons and enhances their mobility. This effect is explained in terms of the point defects in the crystal lattice – formation of substitutional defects thallium on the site of bismuth TlBi and the decrease of concentration of selenium vacancies VSe+2. We also discuss the temperature dependence of the power factor σS2 of the samples. Upon the thallium doping we observe a significant increase of the power factor compare to the parental Bi2Se3. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)