A smooth perovskite film fully covering the substrate is of importance for flexible perovskite solar cells (PSCs). In this study, efficient flexible PSCs are fabricated onto conductive plastic substrate by a two-step coating method under ambient condition. By adjusting the concentration of precursor CH3NH3I (MAI), the morphology and thickness of perovskite layer is effectively tailored, according to SEM and AFM analysis, which consequently gives rise to a thin perovskite layer with smooth surface and smaller grain size. As a result, flexible PSCs with efficiency of 12.7% are prepared under ambient condition, and the excellent mechanical stability of flexible PSCs is also demonstrated with bending test under severe conditions. (C) 2017 Elsevier Ltd. All rights reserved.