Computational exploration of two-dimensional silicon diarsenide and germanium arsenide for photovoltaic applications.

The properties of bulk compounds required to be suitable for photovoltaic applications, such as excellent visible light absorption, favorable exciton formation, and charge separation are equally essential for two-dimensional (2D) materials. Here, we systematically study 2D group IV-V compounds such as SiAs and GeAs with regard to their structural, electronic and optical properties using density functional theory (DFT), hybrid functional and Bethe-Salpeter equation (BSE) approaches. We find that the exfoliation of single-layer SiAs and GeAs is highly feasible and in principle could be carried out experimentally by mechanical cleavage due to the dynamic stability of the compounds, which is inferred by analyzing their vibrational normal mode. SiAs and GeAs monolayers possess a bandgap of 1.91 and 1.64 eV, respectively, which is excellent for sunlight harvesting, while the exciton binding energy is found to be 0.25 and 0.14 eV, respectively. Furthermore, band-gap tuning is also possible by application of tensile strain. Our results highlight a new family of 2D materials with great potential for solar cell applications.