Pronounced photovoltaic response from PN-junctions of multi-layered MoSe 2 on h-BN Nihar R. Pradhan 1,ϯ , Shahriar Memaran 1,ϯ , Zhengguang Lu 1 , Daniel Rhodes 1 , Jonathan Ludwig 1 , Qiong Zhou 1 , Pulickel Ajayan 2 , Dmitry Smirnov 1 & Luis Balicas 1,* Several transition metal dichalcogenides (TMDs) such as MoS 2 , WSe 2 , etc., are semiconducting van der Waals bonded solids which are exfoliable down to single atomic layers 1,2 . Monolayers display unique optical 3,4,5 as well as optoelectronic properties, 6,7 while heterostructures incorporating graphene and multi-layered TMDs display pronounced photoconducting 8 and photovoltaic responses 9 . Rectification and the photovoltaic-effect was also reported for lateral 10,11 and for vertical PN-junctions composed respectively of a WSe 2 monolayer or a stack of WSe 2 /MoS 2 monolayers 12,13 . Here, we report the observation of rectification and enhanced photoconducting as well as photovoltaic, in lateral PN junctions based on multi-layered ambipolar 14 MoSe 2 crystals stacked onto h-BN. Our PN junctions composed of ~ 10 atomic layers are translucent enough to yield photoresponsitivities of 1 A/W, external quantum efficiencies exceeding 30 %, short circuit currents exceeding 10 3 A/cm 2 , and photovoltaic efficiencies surpassing 5 % with fill factors of ~ 70%. These values compare favourably with those of transparent photovoltaic cells 15,16,17 . Given that TMDs can be grown in large area, that their band gap(s) can be tuned by varying composition, and the available strategies for increasing their efficiency, e.g. the use of transparent graphene for contacts and gates 8,9 or the incorporation of plasmonic nanoparticles 18 , our results suggest a remarkable potential for semi-transparent photovoltaic cells composed of just a few layers of TMDs. 1 National High Magnetic Field Laboratory, Florida State University, Tallahassee-FL 32310, USA, 2 Department of Mechanical Engineering and Materials Science Rice University, Houston, TX 77005-1892, USA. ϯ These authors contributed equally to this work. * e-mail: balicas@magnet.fsu.edu