© 2020 Elsevier B.V.Hybrid perovskite solar cells (PSCs) have introduced as a good revolution photovoltaic to meet the green world energy demands. The crystallinity improvement of PSCs is a practical approach to improve the efficacy of PSCs. Double cation formamidinium (FA)/methylammonium (MA) PSCs were fabricated by using a simple sequential deposition process. The mesoporous titanium dioxide (TiO2) layers with 200 nm thickness were used as the electron transport layer (ETL). It was observed that with changing the FA/MA precursor temperature could achieve more desirable perovskite films for photovoltaic applications. Our measurements show that with pre-heating of FA/MA solution at 55 °C the defects on the perovskite layer are well passivated. Besides, the perovskite with better crystallinity and smooth morphology, and the defect-free surface was achieved. It is delightful that perovskite with 55 °C reveals stronger photon absorption and better charge collection. Using the pre-heating approach, a redshift in edge absorption of the perovskite films was observed, indicating a better light-harvesting phenomenon in the corresponding perovskite films. Through optimization of the pre-heating temperature of FA/MA solution, a champion PCE of 13.77% was yielded for PSCs higher than of 10.05% one for pre-heating. Also, modified mixed cation devices revealed higher stability behavior in atmospheric conditions than the reference devices.