The diverse defects within perovskite film, electron transport layer (ETL) and their interface greatly impair the power conversion efficiency (PCE), hysteresis and stability of perovskite solar cells (PSCs). Herein, we propose a synchronous defect passivation strategy by introducing chelating agent containing movable alkali metal cations, i.e. sodium tartrate (STA)/potassium sodium tartrate (PSTA) into SnO₂ aqueous colloidal dispersions to realize the efficient regulation of ETL, perovskite layer and their interface properties. That is, the chelating function and existence of alkali metal ions in additives leads to uniform, less defective and highly conductive SnO₂ ETLs, which provides outstanding platforms for depositing perovskite films with high-quality crystallinity to improve the interfacial charge transfer. In particular, a part of Na⁺ and K⁺ ions of additives can enter into perovskite film through thermal diffusion and passivate the defects by coordinating with under-coordinated halides via ionic interactions or electrostatic adsorption on the negative charged defects at surface and grain boundaries. Such synchronous optimization for ETLs, perovskite and their interface enables the realization of high power conversion efficiencies (PCEs) of 20.38% and 21.14% with reduced hysteresis and improved stability for STA-SnO₂ and PSTA-SnO₂ based PSCs, respectively. This work greatly simplifies the defect passivation process and provides a promising low-cost technique for large-scale manufacturing efficient and stable planar PSCs.