Theoretical investigation on ferroelectric In₂Se₃/Cs₃Sb₂I₉ heterostructures with tunable optoelectronic properties through polarization and doping

Heterostructures are eagerly anticipated in solar energy conversion technologies for photovoltaic and photocatalytic water splitting. Herein, ferroelectric In₂Se₃/Cs₃Sb₂I₉ heterostructures with purposeful improvement in carrier separation are proposed for high-performance photovoltaics and photocatalytic water splitting. The results indicate that the electronic structures, photoexcited carrier transfer, and optoelectronic properties of the In₂Se₃/Cs₃Sb₂I₉ heterostructures are dependent on the polarization direction of In₂Se₃. The type-II band alignments of In₂Se₃/Cs₃Sb₂I₉ heterostructures with reduced band gaps improve the separation of photoexcited carriers and enable their better utilization in photovoltaic and photocatalytic water splitting. Furthermore, the photoexcited carrier transfer paths can be switched between the type-II and Z-scheme by tuning the polarization direction. The In₂Se₃/Cs₃Sb₂I₉-↑-Ⅱ heterostructure is predicted with a power conversion efficiency of 9.54 %, while In₂Se₃/Cs₃Sb₂I₉-↑-Ⅱ and In₂Se₃/Cs₃Sb₂I₉-↓-Ⅱ are prominent catalysts with corresponding solar-to-hydrogen efficiencies of 17.2 % and 7.3 %, and the water-splitting reactions are spontaneous on these two heterostructures under solar irradiation. In addition, substitution doping of In atoms to Sb atoms is a more feasible scheme than biaxial strains for improving the optoelectronic properties of In₂Se₃/Cs₃Sb₂I₉, leading to an increase in the above efficiencies. All the findings about these distinctive properties suggest the potential of In₂Se₃/Cs₃Sb₂I₉ heterostructures for efficient solar energy conversion.