The　additive　engineering　to　hybrid　organic-inorganic　perovskite　precursors　is　an　effective　technique　toward　highly　efficient　stable　photovoltaic　devices,　however,　there　is　still　a　deficiency　in　fundamental　understanding　on　how　these　additives　affect　the　perovskite　film　and　device　performance　as　well.　Herein　is　introduced　a　small　organic　molecule,　DRCN5T,　into　a　double-cation　perovskite　precursor　and　the　function　on　device　performance　is　systematically　investigated.　An　appropriate　amount　of　DRCN5T　into　the　precursor　can　promote　the　crystallization　of　film　with　successful　suppression　of　delta-FAPbI(3)　phase,　reduce　grain　boundaries　and　adequately　passivate　the　native　defect　sites.　In　addition,　the　incorporation　of　DRCN5T　also　regulates　the　energy　level　alignment　of　the　perovskite　to　charge　transport　layer　suitably.　This　leads　to　the　promotion　of　charge　transport,　reduction　in　non-radiative　recombination,　and　boosts　the　efficiency　to　a　value　of　20.60%　with　greatly　reduced　hysteresis　in　the　device.　Moreover,　the　treatment　by　DRCN5T　also　significantly　increases　the　stability　of　the　devices　in　ambient　environment.　These　findings　open　the　gate　to　produce　highly　crystallized　perovskite/organic-molecule　active　layers　toward　commercialization　of　perovskite　solar　cells.