New synthesis of 2D halide perovskites assisted by the Langmuir-Schaefer methodology

Abstract

[EN]Perovskites have emerged as a promising component of photovoltaic cells due to their high efficiency and compatibility with various fabrication processes. In the last years, many efforts have been made to eliminate the structural defects which reduce their quantum efficiency. Surface passivation by organic molecules, twodimensional (2D) halide perovskites, has provided the best results. However, the development of synthesis to obtain high quality materials and the design of solid transfer processes that lead to highly ordered layered films, necessary for the preparation of devices, remains a challenge. Therefore, we report for the first time a new synthesis at the interface assisted by the Langmuir-Schaefer methodology (LS) to obtain 2D lead perovskites passivated with the surfactant octadecylammonium bromide (ODAB). In our synthesis, the ammonium salt was spread on a subphase containing lead and potassium bromides, and then, the monolayer was compressed until achieve a dense monolayer of ODAB and layered perovskite. The monolayer was then transferred to solids using the Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) methodologies. The structural characterization of the films was conducted by absorption UV–vis and Raman spectroscopies, X-Ray diffraction (XRD) and scanning electronic (SEM) and atomic force (AFM) microscopies. Our results demonstrate that the highest coverage was achieved by the LS method. Extensive structural analysis has shown that perovskites contain only a layer of inorganic material between bilayers of the organic material. 2D perovskites prepared by this methodology show higher crystallinity than those prepared by other syntheses.