Understanding the Solution Chemistry of Lead Halide Perovskites Precursors

Identifying the composition of the solvated iodoplumbate complexes that are involved in the synthesis of perovskites in different solution environments is of great relevance in order to link the type and quantity of precursors to the final optoelectronic properties of the material. In this paper we clarify the nature of these species and the involved solution equilibria by combining experimental analysis and high-level theoretical calculations, focusing in particular on the DMSO and DMF solvents, largely employed in the perovskites synthesis. The specific molecular interactions between the iodoplumbate complexes, PbIm2-m, and the solvent molecules, X, were analyzed by identifying the most thermodynamically stable structures in various solvent solutions and characterizing their optical properties trough DFT and TD-DFT calculations. A comparison with the experimental UV-Vis absorption spectra allows for the first time the definition of the number of iodide and solvent ligands bonded to the Pb2+ ion and of the complex formation constants of the involved species.