We present a study of the temperature-dependent electrical conductivity in Sn-doped ZnO polycrystalline thin films with different Sn contents (0, 1, 3, 5, and 7 at.%). The electrical conductivities show unusual temperature dependence in a temperature range of 110-400 K, where electronic spatial potential fluctuations at the grain boundaries are observed. By applying a model supposing potential fluctuations at the grain boundaries we find that the potential barrier height decreases from 0.269 eV down to 0.112 eV and the homogeneity coefficient, which describes the homogeneity of films, decreases from 4.41 to 2.91 with increases in Sn content from 1 at.% up to 7 at.%. From these results, we see that the electron transport is essentially controlled by potential fluctuations at the grain boundaries for Sn-doped ZnO polycrystalline thin films. Our findings could be important for the design of high efficiency solar cell based on ZnO thin films. (C) 2012 Elsevier B. V. All rights reserved.