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.