The development of efficient perovskite solar devices fully fabricated in air conditions at low temperature is investigated. A 10.0% average efficiency was achieved for a CH3NH3PbI3 p-i-n planar perovskite solar cell with null hysteresis processed in an environment with relative humidity as high as 70%. This result was enabled by a fine control over the perovskite precursor composition, adapting the solvent engineering process to ambient air conditions and implementing nickel oxide as hole-transporting layer. The presented strategy contributes towards the establishment of processing methodologies leading to scale up high performance perovskite solar cells where processing in ambient air at low temperature is highly desirable.