Suppressed Biexciton Auger Recombination in Core/Shell FAPbI 3 /NdF 3 Perovskite Nanocrystals With Low‐Threshold Amplified Spontaneous Emission

ABSTRACT The core/shell structures have been widely adopted in traditional semiconductor nanocrystals (NCs) to suppress nonradiative Auger recombination of the biexcitons; however, the functionality of this strategy is still elusive in the emerging perovskite NCs owing to the difficulty of screening out the proper shell materials. Here we have coated the perovskite FAPbI 3 core with the NdF 3 shell to form a quasi‐type‐II energy level alignment, so that the spatial electron‐hole separation can be effectively increased with the further assistance of a built‐in electric field across the core/shell interface. As such, the exciton‐exciton repulsion is significantly enhanced to yield a negative binding energy for the biexcitons, whose suppressed Auger recombination is reflected in the high photoluminescence quantum yield of ∼22% and the long photoluminescence lifetime of ∼2.8 ns. The long biexciton optical‐gain time enables amplified spontaneous emission from the core/shell FAPbI 3 /NdF 3 NCs with a femtosecond‐pumped fluence threshold of ∼5.2 µJ/cm 2 , which is among the lowest values ever reported for the organic‐inorganic perovskite materials. The above findings demonstrate that the biexciton Auger recombination can be effectively controlled in the perovskite NCs with a suitable core/shell structure, thus paving the way toward their prospective applications in both classical optoelectronic devices and quantum information technologies.