The influence of the concentration of a TiCl4 aqueous solution used for post-treatment on the device performance of MAPbI(3-x)Cl(x) perovskite solar cells is investigated. All cell parameters increase after treatment by TiCl4 up to the concentration of 100 mM. The enhancement in the fill factor is mainly attributed to the decrease in the series resistance of the treated cells, which is verified via photovoltaic and electrochemical impedance spectroscopy (EIS) measurements. Moreover, more efficient transport and suppressed recombination of charges in the treated cells are observed via EIS and photoluminescence quenching experiments, leading to an increase in the short circuit current density of the treated cells. As a result, a maximum efficiency of 15.6% is achieved for the cell post-treated with 100 mM TiCl4 solution, which is 1.25 times greater than that of the untreated cell, 12.4%. (C) 2017 Elsevier Ltd. All rights reserved.