Manipulation of Charge Transfer in FeP@Fe₂O₃ Core–Shell Photoanode by Directed Built-In Electric Field

Hematite (Fe2O3) can be suitable when used in a solar energy conversion system, but the short charge diffusion lengths limit its applications. Here, we report the studies of charge transfer ability with a 40 nm Fe2O3 nanorod decorated by a 5 nm iron phosphide (FeP) core–shell structure. By selecting the optimized time of phosphorization (20 min), the photocurrent of FeP@Fe2O3-20 photoanode reached 0.86 mA/cm2, enhanced by 4.10-fold compared with pristine Fe2O3 (0.21 mA/cm2) for water oxidation. Further, the charge transport time reduced by 30% due to the FeP shell that served as the hole transport layer. Compared with Fe2O3, FeP@Fe2O3 has a higher Fermi level, which guides the electron’s transfer from FeP to Fe2O3 to create a space charge layer. The charge balance induces an upward bending of band structure at the FeP and Fe2O3 interface and accelerates the separation of photogenerated electron–holes ascribed to the built-in electric field at the interface. Our studies provide a detailed understanding of carrier dynamics in the core–shell structure, demonstrating a new route to explore high efficiency approaches for solar harvesting.