Perovskite solar cells (PSCs) with a composite mesoporous TiO 2 –In 2 O 3 electron transport layer were constructed and tested. For the formation of the In 2 O 3 overlayer three different molar concentrations of the precursor indium(III) acetylacetonate were investigated (TiO 2 –In 2 O 3 (1) 46 mM, TiO 2 –In 2 O 3 (2) 50 mM and TiO 2 –In 2 O 3 (3) 56 mM). In 2 O 3 was chosen because of its slightly higher conduction band placement compared with TiO 2 which could facilitate the charge transport of the photogenerated electrons from the conduction band edge of the perovskite to the TiO 2 , reducing the recombination rate. The electron transport films were characterized structurally and morphologically, while the electrical properties of the PSCs with the TiO 2 –In 2 O 3 bilayer were examined in detail and compared against cells with pristine TiO 2 . 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-TiO 2 /mp-TiO 2 /(In 2 O 3 )/CH 3 NH 3 I 3−x Cl x /P3HT/Au. The optimum device performance was observed for PSCs with the TiO 2 –In 2 O 3 (2) electron layer, having an improved short–circuit current density and open–circuit voltage, with an overall power conversion efficiency of almost 12.9%. [ABSTRACT FROM AUTHOR]