  Two-dimensional Janus van der Waals (vdW) heterojunctions, referring to the
junction containing at least one Janus material, are found to exhibit tuneable
electronic structures, wide light adsorption spectra, controllable contact
resistance, and sufficient redox potential due to the intrinsic polarization
and unique interlayer coupling. These novel structures and properties are
promising for the potential applications in electronics and energy conversion
devices. To provide a comprehensive picture about the research progress and
guide the following investigations, here we summarize their fundamental
properties of different types of two-dimensional Janus vdW heterostructures
including electronic structure, interface contact and optical properties, and
discuss the potential applications in electronics and energy conversion
devices. The further challenges and possible research directions of the novel
heterojunctions are discussed at the end of this review.
