ZnGeSe₂ monolayer: water-splitting photocatalyst with ultrahigh solar conversion efficiency

Hydrogen production through solar water-splitting offers a clean and renewable solution to tackle the ongoing issues of energy scarcity and environmental pollution. Here, the solar water-splitting performance of the ZnGeSe₂ monolayer was explored via first-principles calculations. Our calculated results reveal that the ZnGeSe₂ monolayer embodies stable configurations and semiconducting properties with direct bandgaps ranging from 1.23 to 1.60 eV under the biaxial strain from -1% to +2%. The generated holes and electrons of the ZnGeSe₂ monolayer are separately distributed because of the intrinsic dipole. The calculated band edges of the ZnGeSe₂ monolayer are demonstrated to be favorable for solar water-splitting. Additionally, the ZnGeSe₂ monolayer exhibits strong optical absorption in the whole visible region. The hydrogen and oxygen evolution reactions can be accomplished without cocatalysts. Of particular significance, the solar to hydrogen (STH) efficiency of the ZnGeSe₂ monolayer reaches up to 32%, far exceeding the economic value (10%). In light of these hallmarks, the ZnGeSe₂ monolayer is demonstrated as an excellent water-splitting photocatalyst.