Abstract This work demonstrates the effectiveness of interfacial engineering and defect passivation in the bulk of mixed perovskite absorber to achieve high performance perovskite solar cells (PSCs). It is found that the extent of I–V hysteresis is most significant in PSCs with a single-layer electron transport layer (ETL) composed of SnO2 quantum dots (QD-SnO2) or SnO2 nanoparticles (NP–SnO2). The hysteresis of the PSCs can be effectively suppressed by adopting a multilayer structure for the ETL to optimize the ETL/perovskite interface. Furthermore, the performance of the PSCs can be enhanced by incorporating a controlled amount of an organic cross linker, 2,2′-(ethylenedioxy)bis (ethylammonium iodide) (EDAI), in the mixed perovskite absorber layers. The experimental results consistently show that incorporation of an optimal amount of EDAI is effective in passivating defect states in the bulk of mixed perovskite as well as the grain boundaries and film surface, while excessive EDAI significantly degrades the photovoltaic (PV) performance of PSCs due to generation of defects and electrically insulating properties of EDAI itself. Owing to the synergistic effect contributed from optimized ETL/perovskite interface and the mixed perovskite thin film, the PSC with an active area of 0.06 cm2 exhibits a champion power conversion efficiency (PCE) of ~19.0% with negligible hysteresis and improved stability. The proposed strategies were also applied to fabricate larger area devices from 0.15 cm2 to 0.85 cm2, exhibiting the PCEs of ~12%–18% with negligible hysteresis.