Perovskite solar cells (PSCs) with a composite mesoporous TiO2-In2O3 electron transport layer were constructed and tested. For the formation of the In2O3 overlayer three different molar concentrations of the precursor indium(III) acetylacetonate were investigated (TiO2-In2O3 (1) 46 mM, TiO2-In2O3 (2) 50 mM and TiO2-In2O3 (3) 56 mM). In2O3 was chosen because of its slightly higher conduction band placement compared with TiO2 which could facilitate the charge transport of the photogenerated electrons from the conduction band edge of the perovskite to the TiO2, reducing the recombination rate. The electron transport films were characterized structurally and morphologically, while the electrical properties of the PSCs with the TiO2-In2O3 bilayer were examined in detail and compared against cells with pristine TiO2. All layers were deposited by the spin coating method and at ambient conditions of temperature and humidity. The structure that was used for the mesostructured PSCs was FTO/c-TiO2/mp-TiO2/(111203)/CH3NH3I3-Cl-x(x)/P3HT/Au. The optimum device performance was observed for PSCs with the TiO2-In2O3 (2) electron layer, having an improved short-circuit current density and open-circuit voltage, with an overall power conversion efficiency of almost 12.9%.