Role of Defects as Exciton Quenching Sites in Carbon Nanotube Photovoltaics

Abstract

Semiconducting single-walled carbon nanotubes (s-SWCNTs) have attracted significant attention as a photoactive component in thin film photovoltaic solar cells and photodetectors due to their strong optical absorptivity and high charge transport mobility. However, the external quantum efficiency (QE) of s-SWCNT/acceptor heterojunction solar cells has been limited by poor exciton harvesting efficiency. Exciton trapping and quenching at defects are a suspected source of loss. Here, we study the influence of defects on bilayer s-SWCNT/C60 planar heterojunction photovoltaic devices via both experiment and modeling. First, diazonium chemistry is used to introduce covalent sp3 sidewall defects to s-SWCNTs at various densities that are estimated using Raman and transient absorption spectroscopy. s-SWCNT/C60 heterojunction photovoltaic cells are then fabricated that show a significant decrease in peak external QE (e.g., from 40% to 8%) with increasing defect density. Second, a diffusion-limited contact quenching M...