Room-Temperature Synthesis of Highly Emissive Copper Halide Nanocrystals

Efficient lead-free and cadmium-free emissive semiconductors are essential for next-generation lighting and display technologies. Copper halides, such as Cs3Cu2I5, have attracted extensive attention in the past few years for their extraordinary optoelectronic properties, excellent environmental stability, and easy solution processability. Copper halide nanocrystals (NCs) can be fabricated using the hot injection approach; however, this approach usually requires sophisticated conditions, such as high temperature and vacuum, which hinder scalability and broader applications. In this work, we report a room-temperature ligand-exchange strategy for fabricating highly emissive Cs3Cu2I5 NCs. Through in situ photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM), we elucidate the critical role of the Cs/Cu ratio in governing the optical and structural properties of the NCs. We also highlight the importance of ligand exchange in terminating crystal growth and achieving colloidally stable NCs, supported by density functional theory (DFT) calculations and Fourier-transform infrared (FTIR) spectroscopy. Guided by these insights, we successfully synthesize highly emissive Cs3Cu2I5 NCs with a narrow size distribution (31.5 ± 2.9 nm) and a superior PLQY of 94.3%, which is comparable to the best results via hot injection. Notably, the PLQY retains 95% of its initial value after 40 days of storage in ambient air. Our approach is also readily extendable to Cs3Cu2Br5 and Cs3Cu2Cl5 NCs, which exhibit promising PLQYs. This work provides a scalable and cost-effective route for synthesizing high-quality copper halide nanomaterials, advancing their potential for integration into next-generation optoelectronic devices.