Electronic and optical properties of two-dimensional III2-VI3 materials with the FE-WZ′ structure

Based on the first-principles calculations, we have investigated the mechanical, phonon, electronic and optical properties of two-dimensional (2D) In₂Te₃ (FE-WZ′ phase) family. The Y(θ) value for all M₂X₃ materials exceeds 67 N/m, with Al₂S₃ exhibiting the best mechanical strength, surpassing to that of MoS₂ (∼124.3 N/m in the x and y directions). Phonon calculations reveal that the acoustic branch with the lowest frequency is mainly dominated by out-of-plane vibrations of the metal atoms and non-metallic atoms. Ga₂Te₃ exhibits dynamic instability due to the softening of the optical phonon branch. Incorporating spin–orbit coupling (SOC) in In₂Se₃ and In₂Te₃ converts them into direct semiconductors. These materials possess an electrostatic potential difference ranging from 0.73 to 2.11 eV, which effectively reduces the band gap required for water splitting in the infrared region. Moreover, the M₂X₃ monolayers with intrinsic electric fields are great coveted photocatalysts for overall water splitting. Remarkably, In₂Se₃ displays a solar-to-hydrogen efficiency of 28.6%, which is significant for commercial applications.