Mesoscopic perovskite solar cells (PSCs) have captured intensive attention in the field of energy conversion due to the advantages of low material cost, simple fabrication process and high power conversion efficiency. Benefiting from the optimization of perovskite absorber deposition approaches, the design of new material systems, and the diversity of device concepts, the efficiency of PSCs have increased from 2.19% in 2006 to a certified 22.1% in 2016. Such extremely fast increasing efficiency enables this photovoltaic technology challenge the current commercialized solar cells. However, typical perovskites of methylammonium lead halides (CH3NH3PbX3, X = Cl, Br, I) are usually sensitive to moisture in ambient air, and thus require an inert atmosphere to process. We demonstrate a moisture-induced transformation of perovskite crystals in a triple-layer scaffold of TiO2/ZrO2/Carbon to fabricate printable PSCs. An additive of ammonium chloride (NH4Cl) is employed to assist the crystallization of perovskite, wherein the formation and transition of intermediate CH3NH3X-NH4PbX3(H2O)2 (X = I or Cl) enables high-quality perovskite CH3NH3PbI3 crystals with preferential growth orientation. Correspondingly, the intrinsic perovskite devices based on CH3NH3PbI3 achieve an efficiency of 15.6% and a lifetime of over 130 days in ambient condition with 30% relative humidity. This ambient-processed printable perovskite solar cell provides a promising prospect for mass-production, and will promote the development of perovskite-based photovoltaics.