Optical Fingerprints of Polynuclear Complexes in Lead-Halide Perovskite Precursor Solutions

Solvent-solute interactions in precursor solutions of lead halide perovskites (LHP) 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 LHP. The formation of [PbI${}_{2+n}$]${}^{n-}$ complexes is often expected in diluted solutions while coordination occurring at high concentrations is not well understood yet. In a combined $\mathit{\text{ab}}\mathit{\text{initio}}$ and experimental work, we demonstrate that the optical spectra of the quasi-one-dimensional iodoplumbate complexes PbI${}_2$(DMSO)${}_4$, Pb${}_2$I${}_4$(DMSO)${}_6$, and Pb${}_3$I${}_6$(DMSO)${}_8$ formed in dimethyl sulfoxide solutions are compatible with the spectral fingerprints measured at high concentrations of lead iodide. This finding suggests that the formation of polynuclear lead-halide complexes should be accounted for in the interpretation of optical spectra of LHP precursor solutions.