Strain-enhanced properties of Janus Si2PAs monolayer as a promising photocatalyst for the splitting of water: Insights from first-principles calculations

In this work, the structural stability and the optoelectronic properties of Janus Si2PAs monolayer are systematically studied via first principles calculations. The calculated phonon spectra confirms the stability of the Janus Si2PAs monolayer. The Janus Si2PAs monolayer is a semiconductor with an indirect band gap of 1.91 eV and shows a moderate band edge position. An optical property analysis reveals that the Janus Si2PAs monolayer has a high optical absorption coefficient (i.e., 2.4 ×105 cm−1) in visible zone, which is higher than monolayer GeAs (105-2 ×105 cm−1). Besides, when considering the biaxial strain effects on the Janus Si2PAs monolayer, a change from a metal to a semiconductor can be obtained. It is also shown that the charge transfer can be significantly adjusted by a biaxial strain. Particularly, a tunable band gap from 1.20 eV to 2.00 eV is a perfect bandgap range, which is excellent for the absorption of visible light. More interestingly, the biaxial strain ranging from 0% to 8% can effectively enhance the visible light absorption of the Janus Si2PAs monolayer (2.2 ×105 cm−1 to 3.6 ×105 cm−1). Moreover, the band edge positions of the Janus Si2PAs under above strain is extremely well qualified for a redox potential. Therefore, our findings reveal that the strain modulated Si2PAs monolayer can be as an excellent photocatalyst for water splitting.