Synergy of ammonium chloride and moisture on perovskite crystallization for efficient printable mesoscopic solar cells.

Organometal lead halide perovskites have been widely used as the light harvester for high-performance solar cells. However, typical perovskites of methylammonium lead halides (CHNHPbX, X=Cl, Br, I) are usually sensitive to moisture in ambient air, and thus require an inert atmosphere to process. Here we demonstrate a moisture-induced transformation of perovskite crystals in a triple-layer scaffold of TiO/ZrO/Carbon to fabricate printable mesoscopic solar cells. An additive of ammonium chloride (NHCl) is employed to assist the crystallization of perovskite, wherein the formation and transition of intermediate CHNHX·NHPbX(HO) (X=I or Cl) enables high-quality perovskite CHNHPbI crystals with preferential growth orientation. Correspondingly, the intrinsic perovskite devices based on CHNHPbI 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.