Review on the graphene/nanotube application in thin film solar cells

We reviewed the effect of graphene and carbon nanotubes as a buffer layer with front and back contacts in thin film solar cells based on CdTe and Cu (In, Ga)(S,Se) materials. Nanolayers reduce material consumption and deposition costs, and result in superior electrical/optical properties, higher conductivity, higher transmittance, and higher thermal stability. They are promising candidates in replacing conventional conductive metallic contacts because their properties can be controlled by altering the number of graphene layers, the concentration of nanotubes, and its alloying/dopant density. For example, a highly-conductive nanolayer with a controllable work function (>5 eV) reduces the back barrier height at the CdTe/nanolayer interface and improves the hole passivation. The nanolayer network reduces the degradation rate by covering the the surface of grains in chalcogenide materials and impeding defect migration along grain boundaries. Nanolayer contacted CdTe and CIGS solar cells perform better than metallic contacted devices in thermal stability and have comparable efficiencies, 14.1% and 19.5%, respectively. Thus, they are a good option for thin film photovoltaics.