Synthesis of zero-dimensional octahedral metal halides through solvent incorporation and their photophysical properties.

Zero-dimensional (0D) metal halides, which feature discrete metal halide octahedra interspersed with large organoammonium cations, are the building blocks of halide perovskites. The optical properties of these materials make them promising candidates in light-emitting devices. However, developing their general design principles remains challenging. Here we report an antisolvent incorporation approach that transforms a broad range of two-dimensional tin iodide perovskites into 0D structures. This approach accommodates diverse organic cations and antisolvent molecules and is extendable to germanium and lead analogues. We show that enhancing the structural rigidity in Sn-based octahedra-modulated by organic packing-increases the radiative recombination rate while decreasing the non-radiative recombination rate, achieving near-unity photoluminescence quantum yield. Ge- and Sn-based structures exhibit large Stokes shifts and microsecond-scale triplet lifetimes due to localized excited states, while their Pb-based counterpart shows faster recombination via triplet-singlet mixing, supported by theoretical calculations. This work offers a versatile synthetic platform for 0D metal halides and deepens our current understanding of excited-state dynamics in halide perovskites.