Ultrasonic-Assisted Synthesis of Lead-Free Cs₂AgBiBr₆ Double Perovskite Nanocrystals for Efficient Photovoltaic and Visible-Light Photocatalytic Applications

Lead halide perovskite nanocrystals (NCs) have demonstrated exceptional optoelectronic properties, making them promising candidates for applications in photovoltaics and photocatalysis. However, their inherent toxicity and instability pose significant environmental and operational challenges. To address these limitations, this study presents a facile, scalable, and environmentally benign ultrasonic-assisted one-pot colloidal synthesis of lead-free Cs 2 AgBiBr 6 double perovskite nanocrystals (DPNCs). The synthesized NCs exhibit a narrow bandgap of 1.92 eV, making them highly suitable for visible-light absorption. Structural characterization via X-ray diffraction (XRD) confirms a cubic crystal structure with lattice parameters of 11.28 Å and space group Fm3 - m , while transmission electron microscopy (TEM) reveals well-dispersed spherical NCs with an average size of ~15 nm. The optical properties were investigated using UV-Vis spectroscopy, demonstrating strong absorption at 437 nm. The photocatalytic performance of Cs 2 AgBiBr 6 NCs was evaluated through the degradation of Rhodamine B (RhB) under visible light, achieving an impressive 93% removal efficiency within 70 minutes. The reaction kinetics followed a pseudo-zero-order model, with superoxide radicals (·O 2 - ) identified as the primary active species responsible for dye degradation. The negatively charged surface of Cs 2 AgBiBr 6 NCs facilitates electrostatic interactions with cationic dyes, enhancing photocatalytic efficiency.