Low‐Threshold Superfluorescence and Phase Dynamics in Quasi‐2D Metal Halide Perovskite Thin Films

Abstract Superfluorescence (SF) is a cooperative quantum emission process characterized by intense, ultrafast bursts of light, with promising applications in quantum photonics. In solid‐state systems, SF typically requires cryogenic conditions, with quasi‐2D hybrid metal halide perovskites being a notable exception where room‐temperature SF has been reported. However, the mechanisms enabling high‐temperature SF in these materials remain poorly understood, and the distinction between SF and amplified spontaneous emission (ASE) is often overlooked. Here, SF in hybrid quasi‐2D perovskite phenylbutylammonium cesium lead bromide (PBA:CsPbBr 3 ) is reported with the lowest threshold fluence recorded to date in perovskites, observed across 78–180 K. The phase behavior of emission under varying temperature and excitation fluence is mapped, identifying transitions between SF, ASE, and spontaneous emission regimes. A simple ab‐initio model has been developed to predict the emission density, correlation, and trace distance for understanding the cooperative phenomena and the unified theory of SF and ASE. The analysis reveals the underlying dynamics that differentiate cooperative from non‐cooperative emission, offering new insight into light–matter interactions in perovskites. These findings deepen the understanding of SF in solid‐state systems and inform the design of quantum optical materials operable at elevated temperatures.