Abstract The defects of grain boundaries and film surface are harmful to the efficiency and stability of perovskite solar cells (PSCs). Defect passivation is an effective strategy to improve the performance of PSCs. In this work, a silane coupling agent 3-aminopropyltrimethoxysilane (APMS) was used as an additive of perovskite light-absorbing layer to passivate defects, thereby significantly improving charge transport, reducing charge recombination and improving device performance. The amino group in APMS can not only form a coordinate bond with the uncoordinated Pb in the perovskite, but also form a hydrogen bond with I (N-H⋯I). The crystallinity and uniformity of perovskite grains were improved obviously. Therefore, the addition of APMS greatly reduces the defects of perovskite and the power conversion efficiency (PCE) increased from 18.85% to 20.72% with less hysteresis. Furthermore, a proper carbon chain can be hydrophobic to improve the moisture stability of the perovskite. The PCE of the device remains 60% of the initial device after being placed at a humidity of 50–60% for 400 h. Therefore, this work proves that the use of silane coupling agents as additives is a promising strategy to achieve efficiency and stable PSCs.