Organic salt mediated growth of phase pure and stable all-inorganic CsPbX (X = I, Br) perovskites for efficient photovoltaics.

All-inorganic CsPbX (X = I, Br) perovskites without organic component are promising for long-term stability but face main challenges of facile fabrication and phase stability. Here we discover a general organic methylamine acetate salt mediated growth method to deposit high quality phase pure and stable CsPbX (X = I, Br) perovskite films via a novel precursor consisting of stoichiometric cesium acetate (CsAc), methylamine halide (MAX) and lead halide (PbX). Interestingly, these organic salts of CsAc and MAX could efficiently promote the crystallization process especially lower the crystallization temperature, but do not introduce the incorporation of organic MA cation into all-inorganic CsPbX perovskites. These phase pure and stable CsPbX perovskites with tunable band gaps can be fabricated into high efficiency photovoltaics. Our organic salt mediated growth of all-inorganic perovskite not only reveals the all-inorganic CsPbX perovskite's unique crystal growth mechanism but also demonstrates their promising application for photovoltaics.