Dominating (111) facets with ordered stacking in perovskite films

Abstract

While (100) facet-dominated FAPbI₃ perovskite films have been readily obtained, (111) facet-dominated ones with higher potential for preventing moisture-induced δ-phase transition are hardly achieved. Particularly, growth kinetics of the (111) facet remains elusive. We herein report (111) facet-dominated perovskite films fabricated via a two-step method by incorporating organic ammonium salts (OASs) into the PbI₂ precursor solution and reveal the underlying facet growth mechanism. The cation of the OAS with a larger size than FA⁺, intercalated into interlayers of PbI₂ in the first step, hinders the insertion of FA⁺ into (100) facet-exposed crystals in the second step, thus inhibiting the growth of (100) facets. In contrast, (111) facets can grow without interference because FA⁺ is located on the external layer, enabling their more favorable growth than that of (100) facets. Moreover, the anion of the OAS retarding perovskite growth prolongs the inhibition of (100) facets, continuously increasing the fraction of (111) facets. The resultant perovskite films dominated by (111) facets with ordered stacking along the out-of-plane direction offer a solar-cell efficiency of 25.23% with improved stability compared to those with mixed (111) and (100) facets. This work provides an effective strategy to obtain highly (111) facet-oriented perovskite films and elucidates additive-engineered growth kinetics.