Halide perovskite solar cells designed using planar architectures are rapidly becoming of high interest due to their low-temperature fabrication process. As the Electron Selective Layer, SnO2 can enhance charge transfer from perovskite to electron transport layers leading to the reduction of charge accumulation at the interface exploiting the larger band offset with perovskite and a higher electron mobility compared with traditional TiO2. Herein, we developed a method for the fabrication of low-temperature planar PSCs under ambient conditions. The scalable Crystal Engineering approach was successfully applied to fabricate the CH3NH3PbI3 absorbing layer on low-temperature planar SnO2 under atmospheric conditions (fully out of glove-box). Photovoltaic characterization showed high-reproducible hysteresis-free planar perovskite solar cells with a maximum power conversion efficiency of 17.6%. The photophysical properties of the PSCs, evaluated by transient photovoltage and photocurrent analysis, showed the excellent capability of SnO2 to extract charge for perovskite. Non-encapsulated n-i-p planar solar cells indicated promising stability under atmospheric conditions, maintaining 90% of the initial efficiency for more than 1000 h. We demonstrate that the scalable air insensitive crystal engineering method is a promising approach for industrialization and fabrication of high efficiency, air-stable, and low-temperature planar perovskite solar cells with high reproducibility fabrication.