Potential SiX (X = N, P, As, Sb, Bi) homo-bilayers for visible-light photocatalyst applications†

It is a challenge to identify suitable low-dimensional materials as photocatalysts for photocatalytic water splitting applications. We have systematically investigated SiN, SiP, and SiAs homo-bilayers that are efficient for water splitting applications, and studied five different possible stacking configurations for these homo-bilayers. Our phonon dispersion curve analysis indicates the dynamical stability of odd stackings for all the studied bilayers. The electronic band structures of these stable stackings of SiX homo-bilayers were studied using GGA-PBE and hybrid HSE06 functional. All the studied systems are semiconductors with electronic bandgaps in the range of 2.488–0.948 eV with the hybrid HSE06 functional. Ultrahigh carrier mobilities of the order of 10⁶ cm² V^?1 s^?1 have been predicted. SiBi (S-I) indicated the highest carrier mobility of 18.1 × 10⁶ cm² V^?1 s^?1 for electrons along the x-direction. Most impressively, we found that the band edge potentials of SiP and SiAs straddle the oxidation and reduction potentials in photocatalytic water splitting. It was observed that only SiN satisfied the oxidation conditions, whereas SiSb and SiBi satisfied the reduction conditions in water splitting. An excellent optical absorption was obtained for SiN, SiP, and SiAs homo-bilayers in the visible region, indicating their potential in photocatalytic water splitting. Further, the electrocatalytic activity towards OER/ORR was investigated using first-principles calculations. The thermoelectric figure of merit was explored, and the highest value of 1.02 was obtained for the SiSb monolayer. Our results indicate that Si-based homo-bilayers display promising potential for visible-light-driven photocatalytic water splitting and thermoelectric applications.