Work

The Chemistry From Tin Iodide Molecular Inks to FASnI 3 Nanocrystals

Year: 2026

Type: article

Abstract: ABSTRACT The controlled synthesis of high‐performance tin halide perovskite nanostructures hinges on the coordination chemistry that governs precursor speciation within molecular inks. Here, we elucidate the complexation dynamics of SnI 2 with two benchmark Lewis bases widely used in nanocrystal syntheses: a strong primary amine (R–NH 2 ) and a weaker substituted phosphine (R’ 3 –P). Correlated in situ 1 1 9 Sn NMR and UV–Vis absorption spectroscopy, supported by density functional theory calculations, reveal that both ligands (L) form monomeric SnI 2 –L adducts, with R–NH 2 consistently exhibiting stronger coordination than R 3 ′–P, as quantified by the intrinsic bond strength index and interaction energies. Higher ligand loadings destabilize SnI 2 –L x complexes, particularly for phosphines, whereas we show that amine‐bound multimeric (SnI 2 ) x (R–NH 2 ) x (x = 2−3) species can be present at low ligand concentrations. These molecular‐level insights directly correlate with nanocrystal formation pathways. Stronger Sn─N coordination drives the emergence of 2D Ruddlesden–Popper phases, while weaker Sn–P interactions favor bulk‐like 3D FASnI 3 nanocrystals due to insufficient stabilization of early‐stage intermediates. Guided by this understanding, an amine‐free, three‐precursor strategy employing a strong zwitterionic ligand enables phase‐pure 3D FASnI 3 nanocrystals with improved optical and colloidal stability. This work establishes a predictive framework for designing robust molecular inks for tin halide perovskites and perovskitoid nanostructures.

Source: Small

DOI: 10.1002/smll.202511842