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.

Regulating excitonic effects in non-oxide based XPSe3 (X = Cd, Zn) monolayers towards enhanced photocatalysis for overall water splitting

“…Notably, under the electrode potential ( U e ) of 1.46 V and 1.38 V for CdPSe 3 and ZnPSe 3 , respectively, both the elementary processes of the hydrogen evolution reaction (HER) exhibit a downhill trend, leading to a spontaneous process. It is worth noting that a moderate external bias of 0.99 V in CdPSe 3 and 0.77 V in ZnPse 3 is sufficient for this reaction, which is significantly lower than the requirements of other non-oxide based GaTeI (1.50 V) and InTeI (1.93 V) photocatalysts, 62 with the help of intrinsic potential of photogenerated electrons ( and ).…”

“…In another instance, our group previously reported indium-based monolayers, GaTeI and InTeI, which were shown to exhibit VBM at a higher position compared to those of conventional metal-oxides. 62 This characteristic resulted in a reduction of the band gap, rendering these materials promising candidates for use in PWS applications. The electronic properties of CdPSe 3 and ZnPSe 3 monolayers are studied for their potential in PWS, following optimization of their lattice parameters and confirmation of their dynamical and mechanical stabilities.…”

“…The typical values of screening length ( r 0 ) for the transition metal dichalcogenides (TMDs) class range from 3 to 5 nm; 72,73 whereas it is 2 to 3 nm in Iodine-based GaTeI and InTeI semiconductors. 62 To determine the 2D polarizability, one can utilize the ab initio derived value of the dielectric constant using the following formula:Employing the stated methodology (more details provided in the ESI†), we computed the excitonic characteristics, specifically, the exciton Bohr radius (or the length of the excitonic extension) and exciton binding energy of isolated monolayers and monolayers in diverse dielectric environments. The exciton Bohr radius serves as a measure of the excitonic localization, where localized excitons exhibit higher binding energy while delocalized excitons manifest smaller binding energy.…”

“…These values are lower compared to the GaTeI and InTeI photocatalysts. 62 The subsequent conversion of H* to H 2 , however, is exothermic at pH = 0. Notably, under the electrode potential ( U e ) of 1.46 V and 1.38 V for CdPSe 3 and ZnPSe 3 , respectively, both the elementary processes of the hydrogen evolution reaction (HER) exhibit a downhill trend, leading to a spontaneous process.…”

“…The typical values of screening length (r 0 ) for the transition metal dichalcogenides (TMDs) class range from 3 to 5 nm; 72,73 whereas it is 2 to 3 nm in Iodine-based GaTeI and InTeI semiconductors. 62 To determine the 2D polarizability, one can utilize the ab initio derived value of the dielectric constant using the following formula:…”