(153a) Polymer-Free near-Infrared Photovoltaic with Single Chirality (6,5) Semiconducting Carbon Nanotube Active Layer

The incorporation of single-walled carbon nanotubes (SWNTs) into next generation solar cells as near infrared absorbers has demonstrated the potential to efficiently harness energy in the 1000nm to 1400nm range. However, SWNT-enabled photovoltaics (PVs) to date have required the use of polymers, which served as either SWNT-wrapping (isolating) agents or as direct components of the photoactive layer. While such layers are expected to increase device performance at the laboratory scale, the use of PV engineered polymers is oftentimes restrictive due to low photostability and the necessity of highly controlled environments for assembly and characterization. In contrast, carbon nanotubes have the strong advantage of being extremely stable in air while at the same time absorbing in the near infrared region of the solar spectrum.  Here, for the first time, we demonstrate a polymer-free carbon based photovoltaic which relies on exciton dissociation at the SWNT/C60 interface. 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 a carbon based solar cell completely free of polymeric active or transport layers, we show both the feasibility of this novel device as well as inform the mechanisms for inefficiencies in SWNT and carbon based solar cells.