Perovskite solar cells (PSCs) may offer huge potential in photovoltaic conversion, yet their practical applications face one major obstacle: their low stability, or quick degradation of their initial efficiencies. Here, a new design scheme is presented to enhance the PSC stability by using low-temperature hydrothermally grown hierarchical nano-SnO2 electron transport layers (ETLs). The ETL contains a thin compact SnO2 layer underneath a mesoporous layer of SnO2 nanosheets. The mesoporous layer plays multiple roles of enhancing photon collection, preventing moisture penetration and improving the long-term stability. Through such simple approaches, PSCs with power conversion efficiencies of approximate to 13% can be readily obtained, with the highest efficiency to be 16.17%. A prototypical PSC preserves 90% of its initial efficiency even after storage in air at room temperature for 130 d without encapsulation. This study demonstrates that hierarchical SnO2 is a potential ETL for fabricating low-cost and efficient PSCs with long-term stability.