Room-Temperature Large-Scale Synthesis of Black-Phase CsPbI₃ Nanocrystals for Red Light-Emitting Diodes

Inorganic perovskite nanocrystals (IPNCs) are gaining attention as next-generation luminescent materials due to their excellent optoelectronic properties and thermal stability. However, current challenges in achieving large-scale synthesis hinder quality improvement and their commercialization. In particular, CsPbI3, which exhibits red emission, stabilizes in a nonradiative yellow phase at room temperature, making it difficult to synthesize the radiative black phase under ambient conditions. Currently, the synthesis of IPNCs is limited to small-scale laboratory procedures. In response to the demand for stable room-temperature synthesis methods of CsPbI3 and the need for large-scale synthesis of IPNCs, we present large-scale synthesis of black-phase CsPbI3 nanocrystals at room temperature by starting from nanostructures and adjusting the Cs-to-Pb ratio to prevent the formation of yellow-phase CsPbI3. The probability of cesium occupying the A site in the perovskite structure (ABX3) varies with the Cs-to-Pb ratio, leading to differences in the growth rate of the nanocrystals. By adjusting the amount of oleylammonium on the surface of the CsPbI3 nanocrystals, we controlled the synthesis process. As a result, we achieved a photoluminescence quantum yield (PLQY) of 72% at 670 nm by synthesizing CsPbI3 nanocrystals in a 1 L bottle, utilizing more than 800 times the compound quantity compared to laboratory-scale methods. Furthermore, we fabricated red light-emitting diodes (LEDs) with an external quantum efficiency of 6.4% and a full width at half-maximum (fwhm) of 33 nm. This room-temperature large-scale synthesis method for CsPbI3 nanocrystals holds significant promise for the future commercialization of inorganic perovskite LEDs.