Capped carbon nanotube photovoltaic cells: Influence of distribution of the five-membered rings on the efficiency

• A photovoltaic solar cell of capped carbon nanotubes (CNTs) is studied theoretically.
• The electronic structure of the CNT with various cap geometries is studied using DFT.
• Efficiency of the heterojunction between capped CNT and ZnPc is calculated.
• Accumulation of the 5566 clusters at the cap improves the efficiency.

Electronic structure and energy conversion efficiency η for a photovoltaic organic solar cell of single-walled carbon nanotubes (CNTs) with various end-cap geometries facing Zn-phtalocyanine are studied based on density functional theory. Accumulation of the 5566 clusters, composed of two five-membered rings and two six-membered rings, at the cap raises the energy of the localized state, which plays a key role in improving the magnitude of η, whereas both the rotational symmetry around the axis and the chirality of the tube seem to be less important in determining the magnitude of η. These properties are explained by a charge transfer from the CNT to the cap.