Built-In Electric Field Hindering Photogenerated Carrier Recombination in Polar Bilayer SnO/BiOX (X = Cl, Br, I) for Water Splitting

Two-dimensional composited materials play more and more important roles due to the wide range of band gap tunability and strong potentials for a hydrogen evolution reaction and oxygen evolution reaction. Here, the novel polar SnO/BiOX (X = Cl, Br, and I) bilayers are constructed with the advantages of narrow band gaps and photogenerated carriers' separations. The band gap of the bilayers can be tuned from 1.09 to 1.84 eV, remarkably improving the utilization of solar energy. The large difference in the effective masses and built-in electric field effectively hampers the fast recombination of photogenerated carriers, which greatly enhances the photocatalytic efficiency. Also, the type-II band alignment guarantees that the two half-reactions could occur at different surfaces. Moreover, the visible light optical absorption and suitable band alignment further confirm that the SnO/BiOX (X = Cl and Br) bilayer is a promising candidate for photocatalytic overall water splitting.