Efficient and Polarized Emission From Cs₃Cu₂Br₅ Nanorods via Dithiol Ligand Exchange

Ternary copper halides, such as Cs₃Cu₂X₅ (X = Cl, Br, or I), are a new class of lead-free nanocrystals with exceptional optical properties, making them promising for photo-down-conversion display applications. However, recent studies on blue-emitting ternary copper halide nanorods (NRs) have reported low photoluminescence quantum yields (PLQY), rendering them inadequate for displays. Using a dithiol ligand-assisted growth method, here we have synthesized Cs₃Cu₂Br₅ NRs with a uniform rod morphology that exhibit an improved PLQY of 63% and a photoluminescence excitation (PLE) anisotropy of 0.201. We used transient absorption spectroscopy to explore the exciton recombination mechanisms and provide insights into the optical performance differences between 1,2-ethanedithiol (EDT) and 1,6-hexanedithiol (HDT)-treated NRs. Density functional theory calculations are conducted to evaluate ligand binding modes, binding energies, and lattice distortion. Our findings indicate that short-chain dithiols (EDT/HDT) enable bidentate ligand-assisted shape control of Cs₃Cu₂Br₅ NRs by displacing long-chain oleate ligands and forming Cu-S^- bonds orthogonal to the preferential growth direction. Control experiments with monothiol ligands show that these ligands demonstrate effective surface passivation but do not promote nanorod elongation. These findings offer new perspectives on the mechanism of nanorod formation, therefore highlighting the potential of developing lead-free semiconductor NRs for optoelectronic applications.