It is a significant challenge to enhance the band alignment sensitivity of MoS 2 -based optoelectronic devices by constructing semiconductor heterojunction. To solve the problem, we incorporate Cu 2 O into MoS 2 to enhance the tunability of electronic structures for the first time by controlling interlayer spacings or electric field ( E field ) using first-principles calculations. A stable van der Waals heterojunction forms between Cu 2 O and MoS 2 based on the negative interfacial cohesive energy and the excellent lattice match. Noteworthily, the bandgap of Cu 2 O/MoS 2 heterojunction varies about 0.2–0.3 eV with a 0.1 V/Å increase of E field , which is more sensitive than that of pure MoS 2 . It is confirmed that the inhomogeneous charge redistribution of heterojunction enhances the tunability of electronic structures. Additionally, the detection wavelength of heterojunction expands from visible to infrared spectrum with E field . These findings motivate more theoretical and experimental work to further study photodetectors with high sensitivity and low power consumption. Graphical abstract