Band Structure Engineering and Optoelectronic Properties of XAl₂Se₄/α-In₂Se₃ (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 XAl₂Se₄/α-In₂Se₃ (X = Mg, Ca, Sr) heterostructures, focusing on the impact of the ferroelectric polarization direction. The calculation results reveal that the band alignment of MgAl₂Se₄/α-In₂Se₃ remains unchanged, whereas CaAl₂Se₄/α-In₂Se₃ and SrAl₂Se₄/α-In₂Se₃ undergo a dynamic transition between Type-I and Type-II configurations upon polarization reversal. When polarization is upward, the bandgap of the XAl₂Se₄/α-In₂Se₃ heterostructure lies at 0.32-0.72 eV, while downward polarization shifts it to 1.37-1.44 eV. Notably, the MgAl₂Se₄/α-In₂Se₃↓ 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.