Lysine-Capped Bi-Based Halide Perovskite (Cs ₃ Bi ₂ Br _9–x I _x , X = 0, 3, 9) Nanoparticles: Unraveling Structure–Property–Function Relationship upon Halide Substitution

Lead-free halide perovskites are reaching their pinnacle of attracting global research interest by intruding into various domains, encompassing everything from fundamental exploration to vibrant applications. Herein, we have synthesized three variants of lead-free Bi-based halide perovskite nanoparticles, Cs3Bi2Br9 (CBB), Cs3Bi2Br6I3 (CBBI), and Cs3Bi2I9 (CBI), controlling their particle size to <10 nm using l-lysine as a capping agent at room temperature. The substitution of iodine in place of bromine increases the interlayer spacing of the two-dimensional (2D) layer from CBB to CBBI, transforming it into an isolated zero-dimensional (0D) structure in the CBI system, as observed by single-crystal X-ray diffraction analysis. Photocatalyzed C–H activation, demonstrated with these three variants, yields the highest conversion for CBB, followed by CBBI and CBI nanoparticles, which correlates with the crystal structure, EIS, and band diagram. This work investigates an in-depth structure–property–function relationship, spanning from crystallography to the physicochemical profile and photocatalytic outcomes, with the aim of probing the interesting science of materials through structural details.