Diiodine-Induced Dimensionality Evolution in Two Antimony(III) Halides for Optimal-Bandgap Photovoltaics

HighlightsDiiodine-induced host-guest assembly drives a 1D-to-0D evolution in antimony(III) halides.This structural transformation narrows the optical bandgap to an optimal 1.46 eV, approaching the Shockley-Queisser limit.Strong sp-orbital hybridization ensures robust visible-light harvesting, with absorption coefficients exceeding 104cm−1.The resulting 0D complex exhibits high intrinsic thermal stability and remains structurally intact after a 6-month ambient exposure.Developing lead-free organic-inorganic hybrid metal halides with strong light-harvesting capabilities and superior stability, while precisely tuning their crystalline phases and electronic structures, remains a key challenge in optoelectronics. Herein, we report a neutral iodine-induced structural transition from a 1D chain-like (C6H11NH3)2SbI5architecture to a 0D dimeric (C6H11NH3)3[Sb2I9]·I2supramolecular host-guest complex. This transformation is achieved via a controlled solution-cooling crystallization process, yielding high-quality bulk single crystals. Crystallographic analysis reveals that N–H···I hydrogen-bonding networks stabilize the organic cations, while halogen bonding interactions anchor the I2guests within the lattice cavities of the [Sb2I9]3−dimeric host. Experimental characterizations, including XRD, TGA, and XPS, confirm the high phase purity and thermal stability of the (C6H11NH3)3[Sb2I9]·I2hybrid and determine its electronic band structure. To further elucidate the underlying mechanisms, theoretical calculations were performed, revealing that strong sp-orbital hybridization yields a high absorption coefficient. The associated dimensional transition narrows the direct optical bandgap to 1.46 eV, approaching the Shockley-Queisser limit and demonstrating strong potential for visible-light harvesting. This work elucidates the role of supramolecular host-guest interactions in modulating the lattice evolution of lead-free antimony-based materials, presenting halogen guest engineering as an effective approach for optoelectronic material design.