Low dimensional materials such as 1D and 2D materials have been under extensive investigations for optoelectronic and energy generation applications. Scientist and engineers have focused much of their attention on the noble prize-winning material, Graphene, an atomically thin layer of graphite. Due to lack of its bandgap, semiconductor applications that require electron-hole separation can be an issue for graphene devices. However, carbon nanotubes (CNTs), which are the 1-dimensional form of graphene, are promising materials for device applications, due to their low dimensionality along with superior mechanical, electrical, and optical properties. One of the major issues in carbon nanotube research has been chirality (metallic or semiconducting) controlled synthesis. Nevertheless, recent carbon nanotube separation techniques have led to synthesizing ultra-pure semiconducting nanotube solution, which offers many advantages for nanoscale device applications. In this talk I will review recent work performed on CNTs/Silicon junctions for optoelectronic applications. I will show that using low purity (mixture of metallic and semiconducting) carbon nanotubes, it is possible to obtain solar cell efficiency as high as 15%. I will also discuss recent results obtained using 99.9% ultra-pure semiconducting carbon nanotube solution on silicon and how it can be used to fabricate cheap pn junctions.

Moreover, new emerging layered 2D transition metal dichalcogenide (TMDCs) such as MoS2 can offer tunable band gaps by changing only the number of layers. Due to weak van der Waals force between their layers, TMDCs enable us to exfoliate atomically thin layers from their bulk forms, analogous to graphene. In my talk, I will discuss the properties and our recent results of these TMDCs, along with the opportunities offered and the challenges faced in creating van der Waals junctions using atomically thin 2D materials for optoelectronic and solar energy applications.