Enhanced visible light absorption performance of SnS 2 and SnSe 2 via surface charge transfer doping.

The layered two-dimensional (2D) SnS 2 and SnSe 2 have received intensive attention due to their sizable band gaps and potential properties. However, it has been shown that the visible light absorption of SnS 2 and SnSe 2 are restricted as photocatalysts and light-harvesting material absorbers for water splitting and high-performance optoelectronic devices. Herein, to enhance the visible light absorption performance of SnS 2 and SnSe 2 , we performed a systematic investigation on tuning the electronic and optical properties of monolayers SnS 2 and SnSe 2 via surface charge transfer doping (SCTD) with the adsorption of molybdenum trioxide (MoO 3 ) and potassium (K) as surface dopants based on density functional theory. Our calculations reveal that MoO 3 molecules and K atoms can draw/donate electrons from/to SnS 2 and SnSe 2 as acceptors and donors, respectively. The adsorption of MoO 3 molecules introduces a new flat impurity state in the gap of the monolayers SnS 2 /SnSe 2 , and the Fermi level moves correspondingly to the top of valence band, resulting in a p-type doping of the monolayer SnS 2 /SnSe 2 . With the adsorption of K atoms, the electrons can transfer from K atoms to the monolayer of SnS 2 and SnSe 2 , making K an effective electron-donating dopant. Meanwhile, the bandgaps of monolayers SnS 2 and SnSe 2 decrease after the MoO 3 and K doping, which leads to the appearance of appreciable new absorption peaks at around ∼650/480 and ∼600/680 nm, respectively, and yielding an enhanced visible light absorption of SnS 2 and SnSe 2 . Our results unveil that SCTD is an effective way to improve the photocatalytic and light-harvesting performance of SnS 2 and SnSe 2 , broadening their applications in splitting water and degrading environmental pollutants under sunlight irradiation.