The emerging interest in tin halide perovskites demands
a robust
understanding of the fundamental properties of these materials starting
from the earliest steps of their synthesis. In a first-principles
work based on time dependent density functional theory, we investigate
the structural, energetic, electronic, and optical properties of 14
tin iodide solution complexes formed by the SnI2unit tetracoordinated
with molecules of common solvents, which we classify according to
their Gutmann’s donor number. We find that all considered complexes
are energetically stable and their formation energy expectedly increases
with the donating ability of the solvent. The energies of the frontier
states are affected by the choice of solvent, with their absolute
values decreasing with the donor number. The occupied orbitals are
predominantly localized on the tin iodide unit, while the unoccupied
ones are distributed also on the solvent molecules. Owing to this
partial wave function overlap, the first optical excitation is generally
weak, although the spectral weight is red-shifted by the solvent molecules
being coordinated to SnI2in comparison to the reference
obtained for this molecule alone. Comparisons with results obtained
on the same level of theory on Pb-based counterparts corroborate our
analysis. The outcomes of this study provide quantum-mechanical insight
into the fundamental properties of tin iodide solution complexes.
This knowledge is valuable in the research on lead-free halide perovskites
and their precursors.