Perovskite solar cells (PSCs) have attracted much attention in recent years. Their metal halide composition holds the promise of achieving highly efficient and cost effective devices due to high quality crystalline perovskite thin films with tunable absorption edge and high extinction coefficient. Fully solution processed devices are advantageous for future large-scale industrial applications. Methylammonium lead iodide (MAPbI3) with a bandgap of 1.55 eV and an absorption onset in the near infra-red (800 nm) is mostly investigated for PSCs since it can absorb photons in both visible and near-infrared solar spectrum. Furthermore, its capability of acting simultaneously as a hole conductor and electron transporter makes it suitable for planar heterojuntion PSCs. Recently, it was observed that replacing the methylammonium cation (CH3NH3+) by a formamidinium cation (CH(NH2)2+) in the lead iodide perovskite lead to a decreased band gap value (1.47 eV) and a shift in the absorption edge to 850 nm of the perovskite thin film. In this research, we report the fabrication of a high efficiency planar heterojuction formamidinium PSCs. The device architecture is defined by a fluorine-doped tin oxide glass substrate coated with a titanium dioxide (TiO2) thin film, a FAPbI3 absorber layer, a 2,2,7,7-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene (spiro-OMeTAD) hole transporting layer and silver electrodes. The purity and quality of the perovskite thin film were determined by UV-vis spectroscopy, X-rays diffraction (XRD) and energy diffraction spectroscopy (EDS). Field emission scanning electron microscopy (FE-SEM) was used to characterize the morphology of the absorber layer. Furthermore, the device performances were studied as a function of the relative humidity (RH) (%).The impact of RH content on the device characteristics and charge carrier dynamics will be discussed. The stability of FAPbI3 based films and devices will be compared to those based on MAPbI3.