Strong Light-Matter Interactions in Heterostructures of Atomically Thin Films

The isolation of various two-dimensional (2D) materials, and the possibility to combine them in vertical stacks, has created a new paradigm in materials science: heterostructures based on 2D crystals. Such a concept has already proven fruitful for a number of electronic applications in the area of ultrathin and flexible devices. Here, we expand the range of such structures to photoactive ones by using semiconducting transition metal dichalcogenides (TMDCs)/graphene stacks. Van Hove singularities in the electronic density of states of TMDC guarantees enhanced light-matter interactions, leading to enhanced photon absorption and electron-hole creation (which are collected in transparent graphene electrodes). This allows development of extremely efficient flexible photovoltaic devices with photoresponsivity above 0.1 ampere per watt (corresponding to an external quantum efficiency of above 30%). The advent of graphene (1) and the subse-quent discovery of its multitude of superiorproperties (2–5) has led to the identifica-tion of many other two-dimensional (2D) crys-tals (6) through both chemical modification of graphene and exfoliation of other layered com-pounds. This new area of research and progres