Surface Modulation, Optics, and Electrochemical Hydrogen Evolution Studies on CdS‐Ag 2 S Superlattice Heterostructures

ABSTRACT 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‐Ag 2 S@octadecyl amine (ODA) random superlattices quantum dots were formed via ligand‐mediated decomposition of [(PPh 3 ) 2 Ag(SCOPh)] and [Cd(SCOPh) 2 ] complexes. Conversely, CdS‐Ag 2 S@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‐Ag 2 S@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‐Ag 2 S@DDT nanorods exhibited a majority charge carrier recombination with band‐edge emission lifetimes (1.63–1.74 ns). Notably, CdS‐Ag 2 S@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 Ag 2 S 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–Ag 2 S@ODA superlattices.