Tailoring the optoelectronic properties and dielectric profiles of few-layer S-doped MoO3 and O-doped MoS2 nanosheets: a first-principles study

Abstract

To gain insights into few layer (FL) van der Waals MoO_3−xS_x/MoS_2−xO_x heterostructures for photocatalytic applications, we analyze how the concentration (x) and location of anionic isovalent atom (S or O) substitutions impact their opto-electronic properties and high frequency dielectric constant profiles. By using density functional theory (DFT) calculations within the HSE06 functional, we show that the electronic band gap of FL MoO_3−xS_x decreases with increasing x, while the dielectric constant profile and absorption coefficient in the UV-vis range increase. The stronger band gap reductions are obtained when S-atoms are located in the internal bulk region of FL MoO_3−xS_x and in interaction with O-atoms of the neighboring layer. Moreover, the conduction and valence band (CB/VB) levels are shifted to higher energy values in the case of the edge location (external surface) of these S-atoms. Thanks to the determination of the thermodynamic diagrams of 4L MoO_3−xS_x and 6L MoS_2−xO_x, we propose optimal heterojunctions made of 4L MoO_3−xS_x with either single-layer (SL) or FL MoS₂ with CB/VB levels compatible with a Z-scheme working principle and with potentials required for photocatalysis applications such as the photolysis of water into O₂ and H₂. This study combined with our previous theoretical investigations on bulk materials and SL provides a thorough analysis of SL–FL MoO_3−xS_x/MoS₂ heterojunctions where the concentration and location of S-atoms in MoO_3−xS_x are key to design efficient materials for water photolysis.