Stability and the electronic and optical properties of two-dimensional iridium trihalides with promising applications in photocatalytic water splitting.

Based on density functional theory (DFT) calculations, we systematically investigate the structural stabilities, mechanical, electronic, and optical properties of an unexplored kind of two-dimensional (2D) material IrX (X = Cl, Br, I) monolayers. Calculations reveal that IrX monolayers have low cleavage energies, making them feasible to be extracted from their 3D layered bulk counterparts, and possess excellent energetic, dynamical, mechanical, and thermodynamic stabilities. The calculated band gaps fall in the range from 1.796 to 2.410 eV, with the conduction band (CB) edge and valence band (VB) edge straddling between the redox potentials of water. Analysis of optical properties shows that the monolayers exhibit large exciton binding energies and good optical absorption in the visible-light and ultraviolet regions. The van der Waals (vdW) heterostructures IrCl:IrBr and IrBr:IrI have type-II band alignment with enhanced charge separation, narrower band gap, and better visible light absorption, suggesting that the heterostructures hold promising applications in photocatalytic water splitting.