Poster detailing experiments that comprised our recent Nano Letters publication.

1. Extremely Efficient Photocurrent Generation
in Carbon Nanotube Photodiodes
Mitchell Senger1, Daniel McCulley1, Andrea Bertoni2, Vasili Perebeinos3, Ethan Minot1
Suspended Carbon Nanotube pn-Junctions
Scanning Photocurrent Microscopy
Suspended CNT pn-Junctions Form Near Ideal Diodes
Introduction
Summary
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 >100% when the electric field is increased to >
10 V/μm. At these high fields, photocurrent spectroscopy reveals extreme
broadening of low-energy exciton peaks. We compare our results to
theoretical predictions for the decay pathways of excitons in CNTs, and
develop a framework to describe the energy dissipation pathways.
Quantum Yield is Larger for Larger Nanotubes
Modeling of S22 Exciton Decay
Extracting Photocurrent Quantum Yield
Enhancing Quantum Yield with Axial Electric Field
Field Dependence of Photocurrent Peaks
Dissociation Pathways of an S22 Exciton
Field Dependence of Photocurrent Quantum Yield
Optical Interference Simulations
Computational Results
Self Consistent Electrostatics Simulations
Field
Exciton Dissociation Theory
𝑆22
𝐼pc
𝑒 Φ 𝐿i
𝑑 ℏ𝜔 = 𝜂22 𝑁𝐿
𝑆22
𝜎𝑐 𝑑 ℏ𝜔
SEM Image of suspended CNT.
1 𝜇m
Low Field (𝐹 < ~5 V/μm) High Field (𝐹 > ~10 V/μm)
1/Le-h (nm-1)
Probabilitydensity(/nm-1)
Free Carriers Bound Carriers
1
3 2
McCulley, et al. Nano Letters 20, 433 (2020).
Based on: McCulley, Senger, et al. Nano Lett. 20, 433 (2020).