Spatially Programmable S-Scheme Heterojunction Photoanodes via Aerosol-Jet Printing for Efficient Solar Water...

S-scheme heterojunctions enable efficient charge separation while preserving the strong redox ability of photogenerated carriers, offering a powerful platform for advanced photoelectrochemical (PEC) water splitting. However, translating such rationally designed heterostructures into scalable, high-performance photoanodes remains a critical bottleneck for conventional fabrication methods. Here, we develop an aerosol-jet printing (AJP) approach to fabricate S-scheme SrTiO₃/g-C₃N₄ heterojunction photoanodes with well-controlled stacking sequences. The interfacial built‑in electric field drives recombination of SrTiO₃ photogenerated electrons with g‑C₃N₄ holes, preserving the strongly oxidizing holes in SrTiO₃ for the oxygen evolution reaction (OER). The SrTiO₃-on-C₃N₄ configuration delivers enhanced PEC water oxidation activity, with a photocurrent density of 2.3 mA cm^{- 2}, double that of single-component and reversed-structure photoanodes. It is found that this enhancement stems from stacking-order-dependent synergy between the heterojunction built-in electric field and semiconductor-electrolyte band bending. Notably, AJP enables fabrication of large-area, module-sized photoanodes, demonstrating practical scalability for device manufacturing. This work provides a controllable, scalable route for the rational design of high-performance S-scheme heterojunction photoelectrodes for PEC water splitting.