The Role of Specific Interactions in the Formation of Perovskite Structures

Using methylammonium lead iodide (MAPbI3) as an example, the process of complexation of molecular particles from solution at the initial stage of crystallization was studied using calculations based on the density functional theory (DFT). The calculations were carried out taking into account solvents widely used in experiments: dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF) and N-methyl-2-pyrrolidone (N-MP) to analyze the structure and energy of iodoplumbate complexes in the form of simple complex [PbI_mX_n]^{2 – m} and polymeric iodoplumbates ([PbI_mX_n]^{2 – m})_x. Reaction schemes for the formation of MAPbI₃ in DMSO and DMF solvents, as well as in DMF–DMSO and DMF–N–MP binary solvents, are proposed based on the calculated energies. Calculations showed the important role of NH–O hydrogen bonds in the formation of iodoplumbate monomers, as well as the imbalance of the energies of the complexes at several elementary stages of the reaction in various solvents (the formation of [PbI₄X_n]^2– is favorable; the formation of [PbI₅X_n]^3– is slowed down. Mixing a small amount of DMSO with DMF results in a better energy balance and, therefore, potentially better equilibrium in the overall crystallization process, and thus a better quality of the perovskite crystal structure.