Our recent studies of In2O3:Sn (ITO) thin films, obtained by spray pyrolysis method, have revealed the unexpected abnormally high values of the power factor (PF) at certain composition and nanostructure of material [1]. PF, which is a product of electrical conductivity and Seebeck coefficient squared, is commonly used as a parameter that characterizes the electric power part during the thermal power conversion. It was found that in our films in temperature range of 300- 500oC PF (~4.5 mW/m·K2) exceeded more than 5-7 times PF values (~0.6-0.7 mW/m·K2) reported earlier in experimental studies and theoretical predictions for ITO bulk material. Such an effect in ITO films was observed at concentrations of tin close to the solubility limit of Sn in In2O3. In addition, these films were characterized by formation of cubic-like crystallites with {100} faceting and average size about 30-40 nm. These film parameters were obtained after optimization of both the temperature of pyrolysis and the rate of film deposition and the content of Sn. Studied films demonstrated the high temporal stability of the thermoelectric parameters during measurements. To explain the observed effect we proposed the model that taken into account the effect of the potential barrier at the crystallites’ interface on the electrical and thermoelectric properties of the films. It is based on an effect of high surface tension of (100) In2O3 surface which facilitates the extraction and segregation of Sn atoms onto grain surface during the growth of the ITO film. This in turn forms the potential barriers at the grain boundaries despite the degeneracy of electron gas in conduction band. Upward band bending arises also as a result of oxygen adsorption on the crystallite surface. In above-mentioned temperature range chemisorbed oxygen is a most reactive with the ITO surface and creates acceptor-like states which are responsible for band bending. In the conditions of highly doped semiconductor the potential barrier exceeds the Fermi energy ~kBT only. Such potential relief provides most favorable conditions for the energy filtering effect for the charge carriers. Potential barrier separates the electrons in such way when low energy electrons do not pass across the grain boundaries and this considerably increases the Seebeck coefficient without the visible drop in electrical conductivity. Numerical simulation was done using so-called modified integrals of differential conductivity based on Boltzmann approximation of relaxation time by electron scattering on polar optical phonons and ionized impurity. These mechanisms of electron scattering are dominating in the total scattering process and the best agreement with experiment was observed in this case. The report contains the experimental and simulated dependences of main thermoelectric parameters vs. Sn content, temperature and electrophysical parameters of ITO films. In fact, we are dealing with a new type of thermoelectric generators, where potential barriers at the grain boundaries are appeared due to a certain self-organized distribution of impurity, i.e. tin atoms, and co-existing oxygen chemisorption. The estimation of so-called figure of merit of thermal conversion ZT allowed concluding that such nanostructures are really promising for practical applications.