Unraveling the Microstructure of Layered Metal Halide Perovskite Films

Abstract

Layered metal halide perovskites are attractive semiconductors for different optoelectronic applications owing to their large structural versatility and rich photophysics. As is the case for the more conventional 3D perovskites, thin films of these materials can be deposited directly from solution. While much attention is focused on thin film microstructure and its relation to device performance for 3D perovskites, relatively little is known about the microstructure of layered perovskites. Herein, a combination of polarized Raman spectroscopy, electron backscatter diffraction (EBSD), and grazing-incidence wide-angle X-ray scattering (GIWAXS) is used to unravel the microstructure of blade-coated films of phenylethylammonium lead iodide ((PEA)2PbI4). For the first time, the feasibility of constructing absolute orientation maps of layered organic–inorganic perovskites using EBSD is demonstrated. Blade-coated films of (PEA)2PbI4 are shown to possess a strong texture, in which the inorganic planes are oriented parallel to the substrate with only minor variations from perfect [001]-alignment. Both EBSD and Raman spectroscopy show that there is no preferred orientation of grains in the in-plane direction. Using GIWAXS, this texture is found to extend throughout the bulk of the film. Understanding and optimizing the texture of thin films is crucial for the further development of layered perovskite devices.