2D Janus piezoelectric iridium trihalide Ir2X3Y3 with potential application in photocatalysts for water splitting

Abstract

The Janus 2D iridium trihalide, Ir2X3Y3 (X, Y = Cl, Br, I and X ≠ Y), has been studied using first-principles calculations. We have shown that all monolayers are stable in energy, thermodynamics, dynamics and mechanics. Electronic calculations based on hybrid functional spin–orbit coupling (SOC) show that they are semiconductors with indirect band gaps ranging from 1.833 to 2.192 eV, and the band edge positions lie between the reduction potential of H+/H2 and the oxidation potential of O2/H2O. BSE calculations show that they have significant optical absorption capability in both the visible and ultraviolet light regions. The high surface area, suitable band gap, suitable band alignment and high optical absorption make them potentially applicable in photocatalytic full water splitting. The broken inversion symmetry generates a built-in electronic field along the z-direction and a significant out-of-plane piezoelectric response with piezoelectric coefficients of d31 ranging from 0.566 to 0.820 pm/V (e31 varying from 39.7 to 85.0 pC/m). The applied field accelerates charge separation and migration, thereby improving their photocatalytic efficiency. Our results would be instructive for synthesis and potential applications in photocatalytic water splitting and electromechanical devices.