Role of semiconducting and metallic tubes in P3HT/carbon-nanotube photovoltaic heterojunctions: density functional theory calculations.

A density functional theory approach is employed to investigate poly-3-hexylthiophene (P3HT) interfaced with both a semiconducting and metallic carbon nanotube (CNT). For the semiconducting CNT, a type-II heterojunction can form, making such an interface desirable as a photovoltaic heterojunction. In contrast, with the metallic CNT, substantial charge redistribution occurs and the interaction is strongly enhanced. The built-in-potential is, however, quite small, and P3HT becomes electrostatically more attractive for electrons. These observations together indicate that, in a photovoltaic heterojunction based on a mixed CNT distribution, the majority of interfaces are with metallic CNTs and inefficient.