Preparation of high-quality and pure phase mixed-organic-cation FA(1-x)MA(x)PbI(3) perovskite film is a big challenge, especially on a porous oxide scaffold for mesoscopic perovskite solar cells. In this study, we fabricated a pure phase of mixed-organic-cation perovskite FA(1-x)MA(x)PbI(3) simply using a conventional two-step method. Effect of chemical composition and morphology on the photovoltaic performance and stability of the mixed-organic-cation perovskite has been studied in details. Results show that the FA(1-x)MA(x)PbI(3) perovskite thin films with a FA(+): MA(+) molar ratio of 0.7:0.3 demonstrate the best photovoltaic performance. Mesoscopic perovskite solar cells fabricated using these FA(0.7)MA(0.3)PbI(3) thin films yield a power conversion efficiency (PCE) up to 16.0%. Moreover, the devices present a superior stability and the unsealed devices exposed in ambient condition (25 degrees C, 50%-60% relative humidity) can maintain their photoelectric performance without apparent PCE loss for up to 20 days. (C) 2017 Elsevier Ltd. All rights reserved.