Scalable fabrication of high-quality crystalline and stable FAPbI3 thin films by combining doctor-blade coating and the cation exchange reaction

Abstract

Formamidinium lead iodide (FAPbI₃) is one of the most extensively studied perovskite materials due to its narrow band gap and high absorption coefficient, which makes it highly suitable for optoelectronic applications. Deposition of a solution containing lead iodide (PbI₂) and formamidinium iodide (FAI) or sequential deposition of PbI₂ and FAI usually leads to the formation of films with a poor morphology and an unstable crystal structure that readily crystallize into two different polymorphs: the photoinactive yellow phase and the photoactive black phase. In this work, 2D 2-phenylethylammonium lead iodide (PEA₂PbI₄) thin films are deposited by a scalable doctor-blade coating technique and used as a growth template for the high-quality 3D FAPbI₃ perovskite thin films which are obtained by organic cation exchange. We report the structural, morphological and optical properties of these converted 3D FAPbI₃ perovskite films which we compare to the directly deposited 3D FAPbI₃ films. The converted FAPbI₃ thin films are compact, smooth, and highly oriented and exhibit better structural stability in comparison with the directly deposited 3D films. These results not only underscore the importance of the employed deposition techniques in fabricating highly crystalline and stable perovskite thin films but also provide a strategy to easily obtain very compact perovskite layers using doctor-blade coating.