Enhancing extraction of photogenerated excitons from semiconducting carbon nanotube films as photocurrent

We study the effect of residual polymer on exciton transport and the external quantum efficiency (EQE) of photocurrent generation in thin film semiconducting single walled carbon nanotube (s-SWCNT)/C-60 heterojunction diodes. Specifically, increasing the s-SWCNT film content from 22% to 43% increases peak EQE from absorption by s-SWCNTs from 15% to 23%. We monitor intertube exciton energy transfer via steady state photoluminescence spectroscopy and determine the length scale for exciton migration via s-SWCNT film thickness dependence of EQE. We observe increased intertube exciton transfer in photoluminescence spectra with increased polymer removal, and EQE-thickness dependence suggests increased intratube exciton transport along isolated pathways. Our results extend the state of the art with respect to the use of s-SWCNT thin films as photoabsorbers in photovoltaics, describe exciton migration in s-SWCNT films, and provide a framework for the design of high efficiency s-SWCNT photovoltaic and photodetector devices. (C) 2012 Elsevier B.V. All rights reserved.