First principles calculations of the electronic configuration and photocatalytic performance of GaSe(Ga2SSe)/MoS2(MoSSe) heterojunctions

Abstract

The electronic structure and photocatalytic performance of GaSe/MoSSe and Ga₂SSe/MoS₂ heterojunctions are systematically investigated by means of first-principles calculations. The outcomes demonstrate that the IV and II stacking patterns feature the lowest binding energies and the shortest interlayer spacing, wherein the A stacking configurations show typical type-II band alignment characteristics which are conducive to fulfill effective separation of electron–hole pairs in space. The electrostatic potential and the CDD indicate the generation of built-in electric fields from MoSSe to GaSe layers and from Ga₂SSe to MoS₂ layers, respectively, in the interfacial domain, providing a theoretical basis for the examination of the photocatalytic mechanism. The two heterojunctions are more preferable for the photocatalytic decomposition of water under acidic and neutral atmospheres at dissimilar pH levels. For the GaSe/MoSSe heterojunction, the band gap follows a monotonic decreasing tendency when the tensile strain increases from 0% to 6%, while in the case of compressive strain, the band gap increases and then decreases, and the heterojunction cannot undertake the water oxidation process when the tensile strain surpasses 2%. Meanwhile, when a compressive strain of 0% to 3% is imposed, the heterojunction redox potential always traverses the redox potential of water, wherein the photocatalytic performance is sustained. For the Ga₂SSe/MoS₂ system, the band gap value decreases monotonically with the exertion of both tensile and compressive strains. Moreover, it is applicable to photocatalytic water decomposition in the strain range of −6% to 6%. The absorption coefficients reveal that the two heterojunction system has a higher peak in the visible range than the corresponding monolayer, indicating a higher light absorption intensity. Furthermore, the electron mobility of heterojunctions along both directions is significantly higher than that of MoS₂ and WSe₂ monolayers, and GaSe/HfS₂ and K₂Se/Cs₂S heterojunctions. These findings propose that both GaSe/MoSSe and Ga₂SSe/MoS₂ heterojunctions can be utilized as potentially better catalysts for the photocatalytic decomposition of water.