Structures and Properties of Methylammonium Iodide Precursors of Halide Perovskites and Implications for Solar Cells: an Ab-Initio Investigation

Halide perovskite materials based on the prototypical CH 3 NH 3 PbI 3 received much attention in recent years, with applications ranging from solar cells to light-emitting diodes. However, many fundamental aspects of the halide perovskite materials remain elusive at the moment, such as the structures and impacts of the methyl ammonium precursors on the halide perovskite properties. In this manuscript, we take one step back to theoretically investigate the monomer and dimer structures of methylammonium iodide, a precursor for the synthesis of the halide perovskite CH 3 NH 3 PbI 3 via the first principles calculations, in order to provide a more complete view of the halide perovskite structures. The calculations show that the hydrogen bonds are found to be the major factor that stabilizes the methylammonium iodide monomers and dimers, while the dimeric structure exhibits geometry with each iodine atom shared by two neighbouring hydrogen atoms in the methylammonium cation molecules. The hydrogen bonds in the methylammonium iodide are proposed to be correlated with the three-dimensional halide perovskite buildup, and the formation of the hydrogen bond that is available in the halide perovskite framework could be “historically” traced back as early as the precursor preparation. The manuscript addresses the importance of the hydrogen bonds in the synthesis and the crystal formation of halide perovskite materials, and anticipates the necessity of the fundamental theoretical understanding of the structures from the halide perovskite precursors to the halide perovskite frameworks.