Efficiently Harvesting Excitons from Electronic Type-Controlled Semiconducting Carbon Nanotube Films

We have employed thin films of highly purified semiconducting carbon nanotubes as near-infrared optical absorber's in heterojunction photo- voltaic and photodetector devices with the electron acceptor C-60. In comparison with previous implementations of more electrically heterogeneous carbon nanotube/C-60 devices, we have realized a 10x gain in zero-bias quantum efficiency (QE) and even more substantial gains in power conversion efficiency (eta(p)). The semiconducting nanotube/C-60 heterojunctions are highly rectifying with a peak external QE, internal QE, and eta(p) of 12.9 +/- 1.3, 91 +/- 22, and 0.6%, respectively, in the near-infrared. We show that the device efficiency is determined by the effective length scale for exciton migration in the nanotube films, confirm the high internal QE via photoluminescence quenching, and demonstrate that the driving force for exciton dissociation at the fullerene-fullerene heterointerface is optimized for diameters < 1.0 nm. These results will guide the development of next-generation high-performance carbon nanotube-based solar cells and photosensitive devices.