Silver Ion‐Mediated [hk1]‐Oriented Sb$_2$ Se$_3$ Crystal Growth for Efficient Photoelectrochemical Hydrogen Evolution

Antimony selenide (Sb $_{2}$ Se $_{3}$ ), a quasi‐1D material with anisotropic photovoltaic properties, is a promising absorber for photoelectrochemical (PEC) water splitting. This work demonstrates a crystal engineering strategy for hydrothermal deposition of preferentially [hk1]‐oriented Sb $_{2}$ Se $_{3}$ films with enhanced crystal quality. Introducing Ag $^{+}$ into precursor solutions fundamentally alters nucleation kinetics by mediating MoO $_{x}$ formation at the Mo substrate interface. This interfacial modification reduces the heterogeneous nucleation barrier and promotes anisotropic [hk1] growth. The resulting Sb $_{2}$ Se $_{3}$ photocathode achieves a photocurrent density of 24.7 mA cm $^{−2}$ at 0 V $_{RHE}$ in 1 m H $_{2}$ SO $_{4}$ and an applied bias photon‐to‐current efficiency (ABPE) of 2.5% compared with pristine counterparts (14.9 mA cm $^{−2}$ at 0 V $_{RHE}$ , ABPE of 1.1%) with superior operational stability. The PEC performance enhancement originates not only from preferential crystal orientation optimizing charge transport, but also from suppressed non‐radiative recombination. This study establishes an effective hydrothermal approach for fabricating high‐performance [hk1]‐oriented Sb $_{2}$ Se $_{3}$ photoelectrodes by ion‐modulated crystal growth.