Band Structure Engineering and Optoelectronic Properties of XAl ₂ Se ₄ /α‐In ₂ Se ₃ (X = Mg, Ca, Sr) Heterojunctions

Two‐dimensional (2D) ferroelectric materials are recently been the subject of considerable research owing to their distinctive atomic‐layer structure and remarkable physical properties. Despite these advances, their application in optoelectronic devices remains constrained by low photoelectric conversion efficiency and a limited narrow spectral response. This work provides a comprehensive characterization of the electronic structure and optoelectronic properties of XAl 2 Se 4 /α‐In 2 Se 3 (X = Mg, Ca, Sr) heterostructures, focusing on the impact of the ferroelectric polarization direction. The calculation results reveal that the band alignment of MgAl 2 Se 4 /α‐In 2 Se 3 remains unchanged, whereas CaAl 2 Se 4 /α‐In 2 Se 3 and SrAl 2 Se 4 /α‐In 2 Se 3 undergo a dynamic transition between Type‐I and Type‐II configurations upon polarization reversal. When polarization is upward, the bandgap of the XAl 2 Se 4 /α‐In 2 Se 3 heterostructure lies at 0.32–0.72 eV, while downward polarization shifts it to 1.37–1.44 eV. Notably, the MgAl 2 Se 4 /α‐In 2 Se 3 ↓ heterostructure features enhanced light absorption and band edges near the water‐splitting redox potentials at pH = 7, suggesting tunable electronic properties and promising photocatalytic and photovoltaic performance, with a theoretical power conversion efficiency up to 11.68%. This work provides a theoretical foundation for rationally designing ferroelectric heterojunctions and offers guidance for developing next‐generation 2D optoelectronic and photocatalytic devices.