Optical Fingerprints of Polynuclear Complexes in Lead Halide Perovskite Precursor Solutions

Solvent-solute interactions in precursor solutions of lead halide perovskites (LHPs) critically impact the quality of solution-processed materials, as they lead to the formation of a variety of poly-iodoplumbates that act as building blocks for LHPs. The formation of [PbI₂₊] complexes is often expected in diluted solutions, while coordination occurring at high concentrations is not yet well understood. In a combined ab initio and experimental work, we demonstrate that the optical spectra of the quasi-one-dimensional iodoplumbate complexes PbI₂(DMSO)₄, Pb₂I₄(DMSO)₆, and Pb₃I₆(DMSO)₈ formed in dimethyl sulfoxide solutions are compatible with the spectral fingerprints measured at high lead iodide concentrations. This finding suggests that the interpretation of optical spectra of LHP precursor solutions should account for the formation of polynuclear lead halide complexes.