Van der Waals heterostructures in ultrathin 2D solar cells: State-of-the-art review.

• Van der Waals heterostructures can be used in atomically thin solar cells. • Van der Waals heterostructure solar cells have enhanced light absorption. • The bandgap can be tuned in the van der Waals heterostructure solar cells. • Van der Waals heterostructure solar cells use a few amounts of the materials. • Van der Waals heterostructure solar cells could approach to high conversion efficiencies. The emergence of 2D materials in recent years has led to the designing of new novel structures that take advantage of the van der Waals forces in the stacking of dissimilar 2D layers on each other. These structures are called van der Waals heterostructures (vdWHs). The vdWHs have been used in several electronic and optoelectronic applications, including photovoltaic devices and solar cells. Application of 2D semiconductor materials in vdWHs allows bandgap tunning and longer exciton lifetimes. The vdWHs solar cells benefit from high conversion efficiencies, enhanced light absorption, and application of a small amount of the active materials due to their atomically thin structure. The inter-layer exciton in the vdWHs has a longer lifetime than individual layers. The thickness of the inserting insulating interlayer can modulate the binding energy strength of the interlayer exciton. This review studies different types of photovoltaic and solar cells devices working based on the vdWHs. The challenges and prospects for developing this type of solar cell have been addressed. [ABSTRACT FROM AUTHOR]