Invited Presentation: Charge Generation and Recombination in SWCNT Photovoltaic Active Layers

Single-walled carbon nanotubes (SWCNTs) have many attractive properties for conversion of sunlight into electricity or solar fuels. In solar conversion schemes where SWCNTs are used as absorptive charge donors, it is critical to understand the processes by which initially created excitons are dissociated to produce free charges. In this presentation, I’ll discuss time-resolved spectroscopy studies exploring how photogenerated excitons produce charges in both neat SWCNT films and bilayer heterojunctions designed to dissociate photogenerated SWCNT excitons. In neat SWCNT films, we find charge generation yields of several percent even in the absence of an intentional exciton dissociation interface. We use a thin film of C₆₀ to dissociate SWCNT excitons by interfacial electron transfer from films containing a variety of SWCNT chirality combinations. In these “bilayer” PV active layers, exciton dissociation efficiency varies with the thermodynamic driving force for electron transfer, as well as a number of morphological bilayer properties. Charge mobility and recombination also vary dramatically with bilayer morphology and the diameter distribution of SWCNTs within the film. I will discuss our current understanding of the mechanisms for charge generation and recombination in both neat and bilayer films, and how this understanding helps us envision ways to improve upon SWCNT PV active layers.