CsPbBr3 nanocrystals experience step temperature variation in flow: Morphology evolution and optical properties

Due to their remarkable suitability for mass production, micro-scale flow strategies for inorganic perovskite nanocrystals (NCs) are rapidly developed. However, the existing microfluidic systems belong to single-stage thermal reactors and cannot achieve temperature adjustment during NC preparation like the hot-injection method to attain beneficial crystallization and growth temperatures. In this work, we designed two-stage microfluidic system with two heating reaction modules to carry out the growth of CsPbBr₃ NCs experiencing dual reaction temperatures in flow. The nanoplatelets formed due to lower precursor combination temperatures in the first stage are mostly transformed into cuboidal NCs by a second heating reaction, improving the stability of the CsPbBr₃ NCs. Furthermore, the mixed morphology probably impedes the amplified spontaneous emission (ASE) performance, so uniform cuboidal NCs (average size of 18.3 nm) have a lower ASE threshold of 4.6 μJ cm⁻² at room temperature. Additionally, this system effectively avoids the precipitation of PbBr₂ precursor at elevated temperatures, thus enabling the successful fabrication of larger-sized NCs (28.2 nm) upon raising the preparation temperature to 250 °C.