The resistivity of SnO2 films fabricated by spray pyrolysis of SnCl4 methanolic solutions can vary over nearly six orders of magnitude depending on the conditions of preparation [substrate temperature, concentration of SnCl4 and nature of the dopant (Cl, F, Sb)]. At low carrier density, the resistivity is determined by charge trapping at grain boundaries. In the case of highly degenerated materials, grain boundaries do not play a role anymore. The film resistivity is fully controlled by the bulk grain electrical properties, which are found to be dependent on the defect structure generated by the dopant. Thanks to Transmission Electron Microscopy, it is shown that chlorine or fluorine incorporation promotes the formation of the same neutral defects, which are {011} cassiterite twins. On the other hand, antimony gives rise to specific charged structural defects which strongly lower the carrier mobility. The electrical transport properties of F-doped SnO2 films are better than those of Sb-doped materials. Considering the interfacial electron transfer with a redox system. Sb-doped electrodes are the most efficient because they achieve the highest carrier density, with performances approaching those of massive metal electrodes.