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 (CH 3 NH 3 PbX 3 , 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 2 /ZrO 2 /Carbon to fabricate printable mesoscopic solar cells. An additive of ammonium chloride (NH 4 Cl) is employed to assist the crystallization of perovskite, wherein the formation and transition of intermediate CH 3 NH 3 X·NH 4 PbX 3 (H 2 O) 2 (X=I or Cl) enables high-quality perovskite CH 3 NH 3 PbI 3 crystals with preferential growth orientation. Correspondingly, the intrinsic perovskite devices based on CH 3 NH 3 PbI 3 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.