The Effect of Short Chain Carboxylic Acids as Additives on the Crystallization of Methylammonium Lead Triiodide (MAPI)

Due to their exceptional properties, the study of hybrid perovskite (HyP) structures andapplications dominate current photovoltaic prospects. Methylammonium lead tri-iodide perovskite(MAPI) is the model compound of the HyP class of materials that, in a few years, achieved, inphotovoltaics, a power conversion efficiency of 25%. The attention on HyP has recently moved tolarge single crystals as emerging candidates for photovoltaic application because of their improvedstability and optoelectronic properties compared to polycrystalline films. To control the qualityand symmetry of the large MAPI single crystals, we proposed an original method that consistedof adding short-chain carboxylic acids to the inverse temperature crystallization (ICT) of MAPI in-butyrolactone (GBL). The crystals were characterized by single-crystal X-ray diffraction (SC-XRD),X-ray powder diffraction (XRPD) and Raman spectroscopy. Based on SC-XRD analysis, MAPI crystalsgrown using acetic and trifluoroacetic acids adopt a tetragonal symmetry "I4cm". MAPI grownin the presence of formic acid turned out to crystallize in the orthorhombic "Fmmm" space groupdemonstrating the acid's effect on the crystallization of MAPI.