Low-Threshold Superfluorescence in Lead Halide Perovskite Nanocrystal Films

Superfluorescence (SF) in a perovskite nanocrystal (NC) system is highly promising for generating coherent and intense light sources, making it valuable for emerging quantum applications. However, achieving low-threshold superfluorescence in an NC system has been hampered by factors such as high nonradiative recombination rate and low packing factor, which restrict further development. Herein, we employed 10-undecynoic acid (UDA) as a protecting ligand for NCs, replacing the traditional oleic acid (OA), and utilized spin coating to form NC films. Ultraviolet (UV) irradiation was employed to catalyze the homocoupling reaction of the alkynyl groups, facilitating the formation of a compact and ordered NC film through an enhanced molecular alignment. Meanwhile, the generation of conjugated ligands from the homocoupling reaction contributes to the excitonic delocalization, which in turn reduces exciton–phonon (EP) scattering and Auger recombination. By a combination of transient absorption (TA) and temperature-dependent photoluminescence (PL) measurements, the lower nonradiative recombination rate of UDA-modified NC films compared to that of conventional OA-modified NC films is confirmed. Based on the UDA-capped NC film, a low-threshold SF of 8.3 μJ cm^–2 is demonstrated at 77 K.