Ambipolar-transporting coaxial nanotubes with a tailored molecular graphene-fullerene heterojunction

摘要

Despite a large steric bulk of C_(60), a molecular graphene with a covalently linked C_(60) pendant [hexabenzocoronene (HBC)-C_(60); 1] self-assembles into a coaxial nanotube whose wall consists of a graphite-like π-stacked HBC array, whereas the nanotube surface is fully covered by a molecular layer of clustering C_(60). Because of this explicit coaxial configuration, the nanotube exhibits an am-bipolar character in the field-effect transistor output [hole mobility (μ_h) = 9.7 × 10~(-7) cm~2 V~(-1) s~(-1); electron mobility (μ_e) = 1.1 × 10~(-5) cm~2 V~(-1) s~(-1)] and displays a photovoltaic response upon light illumination. Successful coassembly of 1 and an HBC derivative without C_(60) (2) allows for tailoring the p heterojunction in the nanotube, so that its ambipolar carrier transport property can be optimized for enhancing the open-circuit voltage in the photovoltaic output. As evaluated by an electrodeless method called flash-photolysis time-resolved microwave conductivity technique, the intratubular hole mobility (2.0 cm~2 V~(-1) s~(-1)) of a coassembled nanotube containing 10 mol % of HBC-C_(60) (1) is as large as the intersheet mobility in graphite. The homotropic nanotube of 2 blended with a soluble C_(60) derivative [(6,6)-phenyl C_(61) butyric acid methyl ester] displayed a photovoltaic response with a much different composition dependency, where the largest open-circuit voltage attained was obviously lower than that realized by the coassembly of 1 and 2.