Photoelectric Properties of Alloyed Mo1–xWxSe2/XSe2 (X = Mo, W) Heterojunctions: A First-Principles Study

This study investigates a monolayer Mo1–xWxSe2 (x = 0, 0.25, 0.5, 0.75, and 1) system via MoSe2 and WSe2 alloying. We select monolayer Mo0.75W0.25Se2, which has a high efficiency for the separation and migration of electrons and holes, as the base material for the heterojunctions. van der Waals heterojunctions (vdWH) of MoSe2/WSe2, Mo0.75W0.25Se2/WSe2, and Mo0.75W0.25Se2/MoSe2 with stable structures are constructed using the AA′ stacking configuration. Electronic structure analysis shows that the carrier transport path can be designed on demand via alloying. The conduction band offset (CBO) and valence band offset (VBO) of the heterojunctions drive photogenerated carrier cross-layer separation, while the presence of the built-in electric field (Eint) affects carrier recombination. The external electric field (Eext) can achieve the dynamic tuning of the band gap characteristics and heterostructure types. Furthermore, it is found that the heterojunction exhibits good optical properties in the ultraviolet region. These findings establish that the MoSe2–WSe2 alloyed heterojunction enables precise engineering of electronic structures and optical properties through composition control and Eext modulation, offering a novel material platform for high-performance optoelectronic devices and valleytronic applications.