The stability issue has become one of the main challenges for the commercialization of perovskite solar cells (PSCs).Formamidinium (FA)-based perovskites have shown great promise owing to their improved thermal and moisture stability.However,these perovskites are suffering from phase transition and sep-aration.Here,a method of incorporating of γ-aminobutyric acid (GABA) and cesium cations into FAPbI3 is developed to improve the phase stability.It is demonstrated that the crystallinity of α-FAPbI3 phase is greatly improved and the phase transition temperature is significantly dropped.The resultant solar cell therefore obtains a champion power conversion efficiency (PCE) of 23.71％,which is one of the highest efficiencies for methylammonium-free PSCs.Furthermore,it shows an impressively enhanced stability under illumination,exhibiting the great potential of FA-based perovskites for efficient and stable solar cells.