Strategic Spatial Segregation in Silicon Photoelectrodes: Decoupling Catalytic and Optical Functions for High‐Efficiency Solar Water Splitting

Photoelectrochemical (PEC) cells based on silicon photocathodes offer promising pathways for solar‐driven hydrogen production, yet face fundamental limitations arising from competing requirements between catalytic activity and optical absorption. Herein, a paradigm‐shifting approach is presented through spatial segregation of functional regions in silicon photocathodes, effectively decoupling these competing requirements while maintaining efficient charge transport. This design comprises precisely engineered catalyst wires surrounded by tapered microwire arrays, where the catalyst region enables efficient electrochemical reactions while the absorption region maximizes light utilization. Through comprehensive electrical simulations, it is demonstrated that selective catalyst placement with Al 2 O 3 passivation maintains high shunt resistance even at practical catalyst coverages. The tapered absorption wire geometry achieves 96.5% absorption with minimal reflection losses, leading to a calculated photocurrent density of 41.55 mA cm −2 , representing a 60% improvement over planar structures. Furthermore, a scalable fabrication strategy is developed utilizing controlled wet etching and selective catalyst deposition, enabling precise realization of these complex architectures. This spatial segregation strategy presents a new direction for high‐efficiency PEC systems, offering broader implications for various solar energy conversion applications.