Surface Modulation, Optics, and Electrochemical Hydrogen Evolution Studies on CdS-Ag₂S Superlattice Heterostructures

Semiconductor superlattice heterostructures with periodic electronic states hold promise for catalysis, photodetectors, and electronic devices. CdS-based superlattice quantum dots are particularly attractive due to exciton dynamics that enhance electron transport across heterogeneous energy states. In this study, CdS-Ag₂S@octadecyl amine (ODA) random superlattices quantum dots were formed via ligand-mediated decomposition of [(PPh₃)₂Ag(SCOPh)] and [Cd(SCOPh)₂] complexes. Conversely, CdS-Ag₂S@dodecane thiol (DDT) ordered nanorod superlattices were produced through thiol-mediated decomposition. High-resolution scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy confirmed the periodic interfaces. Photoluminescence (PL) studies of CdS-Ag₂S@ODA superlattices showed dual-band emissions, with fast band-edge recombination (τ_av = 1.37 ± 0.03 ns) and delayed non-radiative decay (54.44-99.31 µs) from surface trap states. In contrast, CdS-Ag₂S@DDT nanorods exhibited a majority charge carrier recombination with band-edge emission lifetimes (1.63-1.74 ns). Notably, CdS-Ag₂S@DDT nanorod superlattices demonstrated enhanced electrochemical hydrogen evolution in neutral media, outperforming DDT/ODA-capped type-I/II heterostructures. They showed a slightly higher HER overpotential under illumination (1.572 V) than in the dark (1.38 V) at a current density of 10 mA cm^-2, consistent with the metallic character of Ag₂S and interfacial charge accumulation. However, ODA lowers atomic packing and disordered interfacial coupling, limiting HER activity with an overpotential of 1.636 V in CdS-Ag₂S@ODA superlattices.