Insights into the role of iron coordination in the enhanced photoactivity of MAPbI3/iron oxides heterojunctions

Iron oxide-based heterojunctions have garnered widespread interest in the field of photocatalysis due to their outstanding photoelectric properties. However, an in-depth understanding of the relationship between the interfacial structure and electronic properties of these heterojunctions at the atomic scale remains unclear. Access to such knowledge is critical for guiding the design and enhancing the efficiency of novel photocatalyst classes. Herein, a first-principles computational investigation focuses on the interfacial geometry, electronic structure and electron transfer mechanisms of MAPbI₃/α-Fe₂O₃, MAPbI₃/γ-Fe₂O₃ and MAPbI₃/TiO₂ heterojunctions. Compared to the classical MAPbI₃/TiO₂ system, the influence of iron coordination at the two octahedral iron sites of α-Fe₂O₃ and at both tetrahedral and octahedral iron sites of γ-Fe₂O₃ is investigated. It indicates that the stability of the interface on the γ-Fe₂O₃ (111) surface is enhanced by the octahedrally coordinated iron, whereas the subsurface Fe_o2 plays a pivotal role in stabilizing the interface with PbI on the α-Fe₂O₃-Fe_o1 surface. Furthermore, a notable modulation by different iron coordination of the valence band maximum charge distribution at the the α-Fe₂O₃/PbI and γ-Fe₂O₃/PbI interfaces is observed, which is pivotal for the separation and transfer of photogenerated electrons and holes. Combined with the comprehensive analysis of the band structure, electrostatic potential and average plane charge density of the heterojunction, the MAPbI₃/iron oxides heterojunction is consistent with the S-scheme heterojunction mechanism. Molecular adsorption simulations of CO₂, O₂ and H₂O show that the α-Fe₂O₃-Fe_o1/PbI interface stands out with the lowest adsorption energy, indicating its superior photocatalytic potential for CO₂ reduction and dye degradation. These findings provide valuable insights into the design principles of photocatalytic materials, emphasizing the strategic manipulation of iron coordination to optimize iron-based heterojunction performance.