Applications of carbon nanotubes and graphene for third-generation solar cells and fuel cells

Carbon nanotubes (CNTs) and graphene have attracted great attention since decades ago because of their interesting structure and properties and important application in many areas. They can have high conductivity, high specific surface area, high transparency in the visible range and high mechanical flexibility. They have important application in energy conversion systems including solar cells and fuel cells. They have been extensively studied as the transparent electrode and interfacial materials of organic solar cells (OSCs) and perovskite solar cells (PSCs). They are also used as the catalytic counter electrode of dye-sensitized solar cells (DSSCs). In addition, graphene oxide (GO) is exploited as an auxiliary binder of TiO₂ paste for the mesoporous TiO₂ layer of DSSCs, and GO and functionalized CNTs are adopted as gelators of gel electrolyte for quasi-solid state DSSCs. CNTs and graphene also have important application in fuel cells. They can be used as catalyst support for the oxidation of fuels or oxygen reduction reaction (ORR). CNTs and graphene, particularly when doped with nitrogen, can be directly used metal-free catalysts. This article provides a brief review on the application of CNTs and graphene in OSCs, PSCs, DSSCs and fuel cells.