Abstract: Photoelectrochemical water splitting using solar energy, generating oxygen and hydrogen is one of the clean fuel production processes. Inspired by surface-dependent characteristics of Janus structures, a newly designed Janus monolayer Silicon Phosphorous Arsenide (SiPAs) was analyzed with Density Functional Theory (DFT) methods. Hybrid exchange-correlation functional (HSE06) combined with Wannier90-based analysis for electronic and optical properties of SiPAs reveals that it can act as a photocatalyst. SiPAs show an indirect bandgap of 1.88 eV, absorbing visible light range is 350 to 500 nm. The phonon spectrum confirms dynamic stability. The exciton binding energy is computed with GW/BSE methods. The electronic band edge positions are at -5.75 and -4.43 eV, perfectly straddling the water redox potentials. Interestingly the strain application modifies the bandgap and also non-homogenously widens the absorption band. A novel range of photocatalyst designs with Group IV-V elements with great promise for water-splitting, photovoltaic, and narrow bandgap semiconductor (optoelectronics) applications may be feasible.

Key words: Solar water-splitting, Janus structure, Density functional theory, Strain engineering, Optical and electronic property tuning, Optoelectronic