Single‐Photon Superradiance in Giant Rhombicuboctahedral CsPbI ₃ Nanocrystals

Abstract

ABSTRACT 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 CsPbI 3 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 cm 2 , 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 CsPbI 3 NCs as novel near‐infrared emitters and promising candidates for high‐speed quantum photon sources.