Controlled
perovskite growth from solution is crucial for efficient
optoelectronic applications and requires a deep understanding of the
perovskite precursor chemistry. The so-called “chlorine route”
to lead–iodide perovskite, using PbCl2 or MACl additive
as a precursor, is frequently employed to form homogeneous perovskite
layers by retarding perovskite crystallization. To understand the
role of chlorine-containing lead precursors in solution, we analyze
the chemical interaction of PbCl2 and PbI2 precursors
with commonly employed solvents (γ-butyrolactone (GBL), N,N-dimethylformamide (DMF), and dimethyl
sulfoxide (DMSO)) by combining first-principles simulations and experimental
UV–vis spectroscopy in diluted precursor solutions. Ab initio molecular dynamics simulations reveal reduced
solvation and an increased free energy barrier of lead-halide bond
dissociation of PbCl2 compared to PbI2 with
chlorine acting as a stronger ligand, which, in turn, limits the solvent
coordination. In contrast to PbI2, PbCl2 absorption
spectra lack signatures of high-valent [PbCl
n
]2–n
complexes and show low sensitivity
on the employed solvent, as confirmed by combined UV–vis and
excited-state time-dependent density functional theory (TD-DFT) analysis.
Altogether, our data suggest the presence of residual chlorine coordinated
to Pb even in the presence of high iodine excess, which may retard
the perovskite growth and could also lead to chlorine incorporation
within the lead–iodide perovskite crystal.