Tin oxide is an excellent candidate to replace mesoporous TiO2 electron transport layers (ETLs) in perovskite solar cells. Here, we introduced a SnO2 layer by a low-temperature solution process, and investigated its morphology, opto-physical and electrical properties affecting the device performance. We reveal that low-temperature processed SnO2 is self-passivating in nature, which leads to a high efficiency. To further enhance the blocking effect, we combined a compact TiO2 underlayer with the SnO2 contact layer, and found that the bi-layered ETL is superior compared to single layers. The best device shows photovoltaic values in a planar structure with a short-circuit current density (Jsc) of 22.58 mA cm-2, an open-circuit voltage (Voc) of 1.13 V, a fill factor (FF) of 0.78, and a power conversion efficiency (PCE) of 19.80% under 1 sunlight illumination.