Solution speciation in lead iodide-based perovskite precursor inks

Solution species govern crystallization pathways that define the morphology of metal halide perovskite thin films, making understanding their behavior essential for predicting film formation. Despite this importance, the structures of iodoplumbate species in widely used solvents, including N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), remain undetermined. Here, we combine optical absorption spectroscopy, X-ray scattering and spectroscopy, and atomistic simulations to demonstrate solvent coordination strength regulates iodide ligand sharing between Pb centers, thereby shaping iodoplumbate structure in lead iodide (PbI 2 ) and methylammonium lead iodide (MAPbI 3 ) inks. Weakly coordinating DMF promotes iodo(poly)plumbate formation (> 1 Pb 2+ per species), whereas DMSO stabilizes localized iodo(mono)plumbates. Molecular dynamics and computed absorption spectra attribute ~415 nm absorption in MAPbI 3 –DMF to the formation of short-lived polyplumbate structures. In situ GIWAXS connects these solvent-dependent solution populations to solvate intermediate formation during drying, establishing mechanistic insights for predicting and controlling perovskite crystallization through ink formulation.