Unconventional Anisotropy in Excitonic Properties and Carrier Mobility in Iodine-Based XTeI (X = Ga, In) Monolayers for Visible-Light Photocatalytic Water Splitting

Abstract

Two-dimensional materials for efficient visible-light-driven photocatalytic water splitting after the era of TiO2 and other metal oxides are scarce. Recent years have witnessed an upsurge in the research of nonoxide semiconductors for overall photocatalytic water splitting. Herein, XTeI (X = Ga, In) monolayers are demonstrated to be stable water-splitting photocatalysts. Merely 0.1 (0.03) V of additional voltage is required to drive the oxidation evolution reaction by the GaTeI (InTeI) monolayer. As these monolayers exhibit a higher valence band position than traditional metal oxides, implying a narrower band gap, they are suitable as efficient visible-light-driven photocatalysts with an absorption coefficient of ∼10–5 cm–1 in the visible range of the solar spectrum. Anisotropic carrier mobilities favor charge separation and reduce their recombination. Exciton properties have been analyzed in-depth via GW approximation. Exciton spatial extension and exciton binding energy are found to exhibit a highly anisotropic nature. The exciton binding energies of GaTeI and InTeI on different substrates, like SiO2 and h-BN, range from ∼14 meV to ∼0.2 eV, which are even smaller than those in TMDs. These facilitate easier charge separation, making them favorable photocatalysts.