Photovoltaic Effect in an Electrically Tunable van\nder Waals Heterojunction

Semiconductor\nheterostructures form the cornerstone of many electronic\nand optoelectronic devices and are traditionally fabricated using\nepitaxial growth techniques. More recently, heterostructures have\nalso been obtained by vertical stacking of two-dimensional crystals,\nsuch as graphene and related two-dimensional materials. These layered\ndesigner materials are held together by van der Waals forces and contain\natomically sharp interfaces. Here, we report on a type-II van der\nWaals heterojunction made of molybdenum disulfide and tungsten diselenide\nmonolayers. The junction is electrically tunable, and under appropriate\ngate bias an atomically thin diode is realized. Upon optical illumination,\ncharge transfer occurs across the planar interface and the device\nexhibits a photovoltaic effect. Advances in large-scale production\nof two-dimensional crystals could thus lead to a new photovoltaic\nsolar technology.