Field-Enhanced Exciton Dissociation in Carbon Nanotube Photodiodes

Low-dimensional materials may be useful for building solar cells that harness carrier multiplication and circumvent the Shockley-Queisser limit. For example, quantum dot solar cells with an internal quantum efficiency (IQE) > 100% have been reported. In this work, we search for carrier multiplication effects in CNTs. We use individually-contacted, ultra-clean, suspended, semiconducting carbon nanotubes of known chiral index. Previous work on this system showed an IQE ~ 30% when the built-in electric field was ~ 4 V/um. Here we report an IQE ~ 80% when the electric field is increased to ~ 15 V/μm. At these high fields, photocurrent spectroscopy reveals extreme broadening of low-energy exciton peaks. We compare our results to theoretical predictions for field-induced exciton dissociation in CNTs, and develop a framework to describe the energy dissipation pathways.