Efficient Exciton Relaxation and Charge Generation in Nearly Monochiral (7,5) Carbon Nanotube/C60 Thin-Film Photovoltaics

Abstract

We report on photovoltaic diodes based on bilayer heterojunctions between nearly monochiral, polymer wrapped (7,5) semiconducting carbon nanotube photoabsorbing films and C60. The internal quantum efficiencies (IQEs) for exciton dissociation and subsequent charge collection at the nanotubes’ visible E22 and near-infrared E11 and E11 + X resonances are 84% ± 7%, 85% ± 5%, and 84% ± 14%, respectively. The high IQE at each transition shows that recombination losses during relaxation and/or direct dissociation of “hot” E11 + X and E22 excitons are negligible. A peak external quantum efficiency (EQE) of 34% is achieved at the E11 transition. Zero-bias photoresponsivity is invariant up to short-circuit current densities of at least 23 mA cm–2, indicating negligible losses via trion, charge-exciton, and charge–charge recombination relaxation pathways. An open circuit voltage of 0.49 V and power conversion efficiency of 7.1% are achieved in response to monochromatic excitation of the diodes at the E11 transition. The high IQE across multiple spectral windows, invariant photoresponsivity, and attractive open circuit voltage relative to the 1.18 eV optical bandgap demonstrate the future promise of using monochiral and multichiral semiconducting carbon nanotube films for broadband solar photovoltaic applications.