Role of Chloride in the Morphological Evolution of Organo-Lead Halide Perovskite Thin Films

Abstract

A comprehensive morphological study was used to elucidate chloride’s role in CH₃NH₃PbI_3–xCl_x film evolution on a conducting polymer, PEDOT:PSS. Complex ion equilibria and aggregation in solution, as well as the role they play in nucleation, are found to ultimately be responsible for the unique morphological diversity observed in perovskite films grown in the presence of the chloride ion. An intermediate phase that is generated upon deposition and initial annealing templates continued self-assembly in the case of CH₃NH₃PbI_3–xCl_x. In the absence of chloride, the film growth of CH₃NH₃PbI₃ is directed by substrate interfacial energy. By employing the through-plane TEM analysis, we gain detailed insight into the unique crystallographic textures, grain structures, and elemental distributions across the breadth of films grown from precursor solutions with different chemistries. The lattice coherence seen in morphologies generated under the influence of chloride provides a physical rational for the enhancement in carrier diffusion length and lifetime.