The absorption layer is a crucial factor for high-performance perovskite solar cells. In this work, the influence of the two components, methylammonium iodide (MAI) and formamidinium iodide (FAI) on the morphology, optical absorption and photovoltaic performances was systematically investigated. The results revealed that the surface morphologies of MAI/FAI based perovskite films were rougher, and the grain sizes became larger with increasing the FAI concentration. UV-Vis and photoluminescence spectra showed that there was a red shift with enhancing the FAI concentration. By the effective doping of FAI into the pristine MAI based perovskite film, the formation of a delta-FAPbI(3) was successfully inhibited. As a result, the power conversion efficiency (PCE) of the perovskite solar cells based on mixed absorption layers was improved by about 27% compared to the pristine MAI based perovskite device. (C) 2020 Elsevier Inc. All rights reserved.