Abstract Formamidinium lead iodide (FAPbI 3 ) and SnO 2 are a promising pair of halide perovskite and electron transport layer (ETL). However, FAPbI 3 and SnO 2 have inherent problems such as high crystallization temperature of FAPbI 3 and surface defects of SnO 2 like oxygen vacancies. They cause low crystallinity, non‐uniform grain growth, and more interface defects, leading to carrier recombination and leakage current. The passivation of the interface between FAPbI 3 and SnO 2 is an effective process to address these materials issues. Herein, a dual role of lead sulfide (PbS) quantum dots (QDs) in the interface passivation is explored. PbS QDs which are introduced to the interface between FAPbI 3 and ETL, link to Sn‐dangling bonds of SnO 2 ETLs and anchor the iodine atoms of FAPbI 3 . This changes considerably lower nonradiative recombination, achieve a better energetic alignment between ETL and PbI 3 , and facilitate electron extraction, leading to a power conversion efficiency of 21.66%. image