Multifunctional graphene and carbon nanotube films for planar heterojunction solar cells

Graphene and carbon nanotubes, featured with outstanding electronic, photonic and mechanical properties as well as Earth abundancy, are perfect for use as carrier-selective transport and collecting layers in photovoltaics. In recent years, graphene and carbon nanotube films have underpinned significant advancement in the planar heterojunction (PHJ) solar cells, with reduced fabrication cost, improved power conversion efficiencies approaching 20%, and the great potential for scalable deployment. Here we discuss the state-of-art progress in graphene-based and carbon nanotube-based PHJ solar cells leveraging advanced nanocarbon technologies as well as industrial-compatible solar cell design and processing. Fabrication and functionalization strategies of graphene and carbon nanotube films for electronic and photonic optimization of PHJ solar cells are systematically reviewed. We also envision technological pathways and future prospects to exploit multifunctionality of graphene and carbon nanotubes to realize ubiquitous application of high-performance, flexible PHJ solar cells.