Dominating (111) Facets with ordered stacking in Perovskite Films

Abstract

While (100) facet-dominated FAPbI3 perovskite films have been readily obtained, another top-performing (111) facet-dominated ones with higher potential in 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 by the two-step method with an organic ammonium salt (OAS) incorporated into PbI2 precursor solution, and reveal the underlying facet growth mechanism. The cation of OAS with a larger size than FA+, intercalated into interlayers of PbI2 in the first step, hinders insertion of FA+ into (100) facet-exposed crystals in the second step, inhibiting growth of (100) facets. In contrast, (111) facets can grow without interference because FA+ locates on the external layer, enabling their more favorable growth than that of (100) facets. Moreover, the anion of OAS retarding perovskite growth prolongs the inhibition of (100) facets, continuously promoting 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 elucidate additive-engineered growth kinetics.