LAUSR

Green and amplified spontaneous emissions with low thresholds are crucial for the development of solution‐processable perovskite light sources. Although mixed‐cation CsPbBr3 perovskites are highly promising, pinholes are inevitably formed during the spin‐coating process, which results in considerable optical losses. This study proposes a solvent recrystallization strategy to reduce the number of pinholes and enhance the crystallinity of (Cs, FA, MA)PbBr3/NMA (FA = CH(NH2)2, MA = CH3NH3, and NMA = C11H9NH3) films in a dimethyl sulfoxide gas environment. Amplified spontaneous green emissions are produced with a low threshold of 1.44 μJ cm−2 and a high net modal gain of 1176 cm−1. The reduced threshold is attributed to the relatively low propagation loss and suppressed Auger recombination, which results from the formation of a pinhole‐free surface and enlarged grain size. These results can be utilized in the development of high‐performance perovskite laser devices.