Organic-inorganic lead halide perovskites (LHP) are promising materials for photovoltaic applications. The focus has been on compositional optimization of the LHP layer, without much understanding of the effects of the compositional mixing on structure, in particular, on texture. For this reason, it is important to understand the mechanisms that drive textured LHP. This work examines the effect of stoichiometry, composition, and moisture on the structure of LHP by grazing-incidence wide-angle scattering (GIWAXS). In addition, we analyze the effect of texturing on the optoelectronic properties of the material. First, it is shown that for CsMAFAPb(IBr)<sub>3</sub> films with an excess organic halide, the exposure to moisture induces a crystallographic re-orientation into the texture in the (001) plane. The re-crystallization enhances the photocurrents and long-term stability. Second, to examine the individual effect of the A-site cation and X-site halide in these materials, pure and mixed compositions were analyzed. This work shows the importance of understanding what triggers orientation in the structure of LHPs to enhance the electronic properties of the material, especially, charge carrier extraction.

Understanding the effects of moisture, stoichiometry, and composition on the texture of lead halide perovskites

ACS Fall 2021

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