First-Principles Study on Janus-Structured ScCX/ScCY (X, Y = F, Cl, Br) Heterostructures for Solar Energy Conversion.

Two-dimensional van der Waals heterostructures have good application prospects in solar energy conversion due to their excellent optoelectronic performance. In this work, the electronic structures of ScCF/ScCCl, ScCF/ScCBr, and ScCCl/ScCBr heterostructures, as well as their properties in photocatalysis and photovoltaics, have been comprehensively studied using the first-principles method. Firstly, both of the three thermodynamically and dynamically stable heterostructures are found to have type-II band alignment with band gap values of 0.58 eV, 0.78 eV, and 1.35 eV. Meanwhile, the photogenerated carriers in ScCF/ScCCl and ScCF/ScCBr heterostructures are predicated to follow the direct Z-scheme path, enabling their abilities for water splitting. As for the ScCCl/ScCBr heterostructure, its photovoltaic conversion efficiency is estimated to be 20.78%. Significantly, the light absorption coefficients of ScCF/ScCCl, ScCF/ScCBr, and ScCCl/ScCBr heterostructures are enhanced more than those of the corresponding monolayers. Moreover, biaxial strains have been observed to considerably tune the aforementioned properties of heterostructures. All the theoretical results presented in this work demonstrate the application potential of ScCX/ScCY (X, Y = F, Cl, Br) heterostructures in photocatalysis and photovoltaics.