Single-Photon Superradiance in Giant Rhombicuboctahedral CsPbI₃ Nanocrystals

Increasing the volume of halide perovskite nanocrystals (NCs) is generally accompanied by lower photoluminescence quantum yield (PLQY). Here, we overcame this trade-off with giant (25 nm) rhombicuboctahedral CsPbI₃ NCs that retain an exceptional PLQY of 87%. Their distinct size and morphology were induced by using phenacyl iodide as a novel precursor and subsequently characterized by x-ray diffraction and transmission electron microscopy. In these giant NCs, the non-radiative Auger process is suppressed, giving rise to a high biexciton PLQY of 55%, while a high single-photon purity up to 95% was achieved using a time-gating method. Benefiting from their enlarged volume, these NCs achieve one of the largest reported absorption cross-sections of 5.3 × 10^-13 cm², along with emission tunable to the near-infrared region (>700 nm) and a prolonged room-temperature lifetime of 465 ns-nearly an order of magnitude longer than conventional NCs. In contrast, at cryogenic temperatures, these enlarged NCs exhibit narrow and ultrafast emission (τ = 467 ps) arising from the coherent coupling of dipoles within a single NC, which induces a giant oscillator strength and leads to single-photon superradiance. These results position the unique rhombicuboctahedral, giant CsPbI₃ NCs as novel near-infrared emitters and promising candidates for high-speed quantum photon sources.