Ligand Engineering and Recrystallization of Perovskite Quantum‐Dot Thin Film for Low‐Threshold Plasmonic Lattice Laser

Abstract Solution‐process perovskite quantum dots (QDs) are promising materials to be utilized in photovoltaics and photonics with their superior optical properties. Advancements in top‐down nanofabrication for perovskite are thus important for practical photonic and plasmonic devices. However, different from the chemically synthesized nano/micro‐structures that show high quality and low surface roughness, the perovskite QD thin film prepared by spin‐coating or the drop‐casting process shows a large roughness and inhomogeneity. Low‐roughness and low‐optical loss perovskite QD thin film is highly desired for photonic and optoelectronic devices. Here, this work presents a pressure‐assisted ligand engineering/recrystallization process for high‐quality and well‐thickness controlled CsPbBr₃ QD film and demonstrates a low‐threshold and single‐mode plasmonic lattice laser. A recrystallization process is proposed to prepare the QD film with a low roughness (RMS = 1.3 nm) and small thickness (100 nm). Due to the low scattering loss and strong interaction between gain media and plasmonic nanoparticles, a low lasing threshold of 16.9 µJ cm⁻² is achieved. It is believed that this work is not only important to the plasmonic laser field but also provides a promising and general nanofabrication method of solution‐processed QDs for various photonic and plasmonic devices.