This work report results concerning the effect that the substitution of the methylammonium cation by the formamidinium cation causes on the properties of FAx(MA1-x)PbI3films synthesized by spin coating in one step. For that, it was conducted a study to establish the influence of the composition of the FAx(MA1-x)PbI3films on their optical, structural and morphological properties, determined through spectral transmittance, atomic force microscopy and X-ray diffraction measurements. Correlating parameters of synthesis with results of the study of properties performed, we were able to get conditions to grow FAx(MA1-x)PbI3films with improved optical gap, microstructure and morphology, what allows to think that this compound is suitable to be used as the active layer in hybrid solar cells.