Investigating Exciton Dissociation Yields in Single-Walled Carbon Nanotube/Fullerene Blends

Semiconducting single-walled carbon nanotubes (s-SWCNTs) have a number of remarkable optical and electrical properties including tunable band gaps and high charge mobilities that make them appealing for use in photovoltaic devices. Using narrow chiral distributions of large-diameter (d > 1.2 nm) s-SWCNTs can be beneficial to these devices through increased carrier mobility and reduced trapping due to energetic differences between different chiralities. Another benefit of using larger diameter SWCNTs is their lower exciton binding energies, which must be considered when designing a blend with sufficient driving force for charge separation. Additionally, much of the visible and near-infrared region of the solar spectrum can be covered by appropriately tuning the diameter range of these s-SWCNTs along with careful selection of the fullerene acceptor material. Time-resolved microwave conductivity (TRMC) was used to explore charge separation in such s-SWCNT:fullerene (donor:acceptor) blends. TRMC allows for sensitive monitoring of charge generation and decay in response to photoexcitation. We will report on dynamics of charge generation and changes to free carrier yield in blends using carefully tuned combinations of SWCNT diameters and fullerene acceptors. Furthermore, we will discuss how these results can be used to design enhanced s-SWCNT:fullerene active layers.