MoSi2N4/MoGe2N4 heterojunction: A theoretical exploration for high-efficiency excitonic solar cell and visible-light photohydrolytic catalyst

Solar cells and photocatalytic water splitting are both viable, environmentally friendly strategies for producing sustainable energy. However, the utilization of freestanding monolayer is typically limited by their poor stability, limited light harvesting and rapid carrier recombination. Inspiringly, this issue can be effectively resolved by building heterojunctions with freestanding monolayers. In this work, we construct a van der Waals MoSi2N4/MoGe2N4 heterojunction and systematically investigate its stability, electronic traits, light absorption behavior, and carrier dynamics. Interestingly, the MoSi2N4/MoGe2N4 heterojunction is an indirect semiconductor with a bandgap of 1.39 eV and exhibits type-II band alignments. Moreover, it is an excitonic solar cell candidate with a high power conversion efficiency of 19.62%. Additionally, the MoSi2N4/MoGe2N4 heterojunction shows promise as a photocatalyst for water splitting, thanks to its favorable band edge positions and Gibbs free energy diagrams. Furthermore, the MoSi2N4/MoGe2N4 heterojunction exhibits strong visible-light absorption ability, and its carrier lifetime is evaluated to be 7.2 ns. Therefore, the MoSi2N4/MoGe2N4 heterojunction is a candidate for solar energy utilization in solar cells and photocatalysts.