Phase‐Pure and Size‐Tunable Tin Halide Perovskite Quantum Dots

QDs, finely tunable between 4 and 22 nm, providing access to size-dependent optical bandgap energies across the strong-to-weak confinement regimes. Increasing the availability of Sn(II) through an additional tin carboxylate source reduces defect densities and leads to the emergence of pronounced and spectrally well-resolved excitonic absorption in strongly confined QDs. Variation of the tin halide and A-cation yields formamidinium, methylammonium, and cesium tin bromide and iodide, all with narrow size distributions. This synthetic route sets the stage for further defect engineering to yield bright tin halide perovskite emitters.