The pristine TiOx and Zn-doped TiOx films with the different Zn/Ti doping ratios were prepared by a sol-gel method on ITO substrates, and used as electron transfer layers in inverted organic solar cells based on P3HT:PCBM. The highest electron mobility was achieved in the film with a Zn/Ti atomic ratio of 0.8%. The photovoltaic device based on the 0.8% Zn-doped TiOx film had a power conversion efficiency of 3.39%, increased by similar to 35%, compared with 2.51% of the reference device based on the pristine TiOx film. The electrochemical impedance analysis revealed that the optimal device based on the 0.8% Zn-doped TiOx had the smallest charge transport resistance and the smallest charge transport time constant in all devices. The fast electron transport on the interface between the organic active layer and ITO cathode increased the open circuit voltage and short-circuit current density of inverted organic solar cells. (C) 2013 Elsevier Ltd. All rights reserved.