Anisotropic Janus monolayers BXY (X = P, as or Sb, Y = S, Se or Te) for photocatalytic water splitting: A first-principles study

Recent advancements in two-dimensional materials have unveiled their promise in various applications, particularly in the realms of optics, electronics, and optoelectronics. This study presents a theoretical exploration of a novel class of anisotropic Janus monolayer materials, BXY (with X being P, As, or Sb, and Y being S, Se, or Te), utilizing first-principles density functional theory. Our stability analysis reveal that the eight of these monolayers exhibit high stability, with the exception of BSbS. Through the application of the HSE06 hybrid functional, We've identified that these stable monolayers fall into the category of semiconductors with an indirect bandgap, and their band gaps span a range between 0.35 and 3.00 eV. Except for BSbSe, all other semiconductors fulfill the band edges criteria in photocatalytic water splitting. Additionally, we have observed that these materials possess anisotropic and superior carrier mobility and optical absorption properties, attributed to their distinct anisotropic structure. As for the solar-to-hydrogen (STH) efficiency, five of these monolayers exhibit STH efficiencies that go beyond the 10 %, with BAsS and BSbTe reaching notable values of 33.93 % and 36.11 %, respectively. Furthermore, the synergistic effects of photoexcitation and electrocatalysis in these monolayers facilitate the overall water splitting process. Additionally, we explored how uniaxial and biaxial strain impact the electronic, optical absorption, OER, and HER activity, as well as the STH efficiency, of these stable monolayers. We found that a small range of uniaxial strain (-2% to 2 %) can enhance their STH efficiency. In our study, we concluded that BSbTe is the most suitable material for photocatalytic water splitting.