Two-dimensional Janus XWZAZ′ (X = S, Se, Te; A = Si, Ge; Z, Z′ = N, P, As): candidates for photocatalytic water splitting and piezoelectric materials

Due to their extraordinary properties, particularly the presence of an inherent electric field that effectively suppresses the recombination of photogenerated carriers, Janus two-dimensional (2D) materials exhibit strong light absorption and high solar-to-hydrogen conversion efficiency, making them promising candidates for photocatalytic water splitting applications. In this study, we conducted first-principles calculations to investigate the layers XWZAZ' (X = S, Se, Te; A = Si, Ge; Z, Z' = N, P, As; Z ≠ Z'). Out of 36 possible structures, 25 were found to be stable in terms of their dynamic, thermal, and mechanical properties. Among these 25 stable structures, 22 exhibit semiconductor behavior. Notably, 9 of these semiconductor structures demonstrate excellent photocatalytic and light absorption properties. These 9 photocatalysts possess remarkable light absorption rates (∼23%), high solar-to-hydrogen energy conversion efficiencies (38.447%), ultra-high carrier mobilities (101 596.37 cm² s^-1 V^-1), and spontaneous hydrogen evolution reaction (HER) capabilities. Furthermore, all 22 semiconductor structures display significant piezoelectric responses both in-plane and out-of-plane, and biaxial strain has a considerable impact on the properties of the 25 stable structures. This study not only provides potential candidate materials for photocatalytic and piezoelectric applications but also offers theoretical guidance for addressing energy crises and environmental pollution challenges.