The variations of the Hall constantRH, Seebeck coefficient α, reflectance spectra in the plasma-resonance frequency range and shift of the absorption edge due to the incorporation of Pb atoms into the crystal lattice of Bi2Se3single crystals, show that Pb impurities at low concentrations lead to an increase of the free charge carrier (electron) concentrationnin the crystals; at higher concentrations a decrease ofnvalues is observed. The anomaly in then=f(cPb) dependence is accounted for by a model based on the assumption that the arising Pb'Bisubstitution defects interact with native defects in the crystal lattice of undoped Bi2Se3; i.e. with antisite Bi'Sedefects and V−Sevacancies in the selenium sublattice. Fitting then=f(cPb) dependence allows us to conclude that the formation energy of Bi'Sedefects increases with increasing content of Pb content in the crystal lattice. It is shown that simultaneous changes of the concentration of the considered defects, Pb'Bi, Bi'Seand V−Se, are responsible for the maximum observed on then = f(cPb) dependence in the range of low Pb concentrations.