Polymer-Free Near-Infrared Photovoltaics With Single Chirality (6,5) Semiconducting Carbon Nanotube Active Layers

The addition of single-walled carbon nanototubes (SWNTs) into next generation solar cells as either near infrared absorbers or directional charge transporters has shown the potential to increase device efficiencies. Previous measurements of single and few tube devices implicate nanotube-nanotube junctions in exciton recombination, limiting efficiency. Here, we ask if this limitation scales to an all nanotube hole conducting phase, or the unity volume fraction limit of an all carbon device. We create such a (6,5) SWNT/C60 photovoltaic device for the first time. Devices yielded 0.5% external quantum efficiency (EQE) at the peak of the nanotube absorption spectrum and a power conversion efficiency of 0.10% under AM1.5 illumination. Interestingly, this value exceeds many of those reported for polymer/SWNT/PCBM composite based photovoltaics. Further, the addition of only 20% (6,4) SWNTs to an otherwise pure (6,5) SWNT film reduces device efficiency 30 times, demonstrating the importance of an energetically homogeneous film with respect to SWNT chirality. Through the construction of an all-carbon photovoltaic, we show both the feasibility of this novel device as well as inform the mechanisms for inefficiencies in SWNT based solar cells.