The Role of Defects as Exciton Quenching Sites in Carbon Nanotube Photovoltaics

TitleThe Role of Defects as Exciton Quenching Sites in Carbon Nanotube Photovoltaics
Publication TypeJournal Article
Year of Publication2017
AuthorsWang J, Shea MJ, Flach JT, McDonough TJ, Way AJ, Zanni M T., Arnold MS
Secondary TitleJournal of Physical Chemistry C
Date Published03/2017
PublisherJournal of Physical Chemistry C

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 one suspected source of loss. Here, we study the influence of defects on bilayer s-SWCNT/C60 planar heterojunction photovoltaic devices via both experiments 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 Monte Carlo model is developed to assess the contributions of exciton quenching defects on exciton migration in bilayer s-SWCNT/C60 heterojunction devices. The model indicates that current state-of-the-art s-SWCNT-based devices are defect-limited and suggests that significant gains in exciton harvesting efficiency could be realized if more pristine, longer s-SWCNTs were utilized.