2D XBiSe₃(X = Ga, In, Tl) monolayers with high carrier mobility and enhanced visible-light absorption

The geometrical configurations of the XBiSe₃ (X = Ga, In, Tl) monolayers are identified by employing the first-principles density functional theory calculations, and the stabilities are confirmed by phonon dispersion, formation energy, and ab initio molecular dynamics simulation, respectively. The bandgap and band edges, the density of states, the optical absorption, mobility, and effect of strain engineering are evaluated to understand the photoelectronic properties of the monolayers. The results show that the XBiSe₃ monolayers have the indirect bandgaps of 1.14-1.69 (1.20-1.84) eV by HSE06(GW), leading to the enhanced optical absorption from the visible to near-ultraviolet region. The large mobility of the electron and hole are also observed, which is helpful for the separation and transfer of the photogenerated carrier pair. The band edges and bandgaps, as well as the optical absorptions, can effectively be tuned by strain engineering. It should be noted that the band edges of the InBiSe₃ monolayer could satisfy the condition of redox potential for the hydrogen evolution reaction under the compressive strain heavier than -3%, implicating this monolayer can also be used for photocatalytic water splitting to produce hydrogen. Therefore, these monolayers have potential applications in photocatalytic materials or photoelectronic devices such as energy harvesters and visible-light sensors.