2 research outputs found
Understanding Charge Transport in Mixed Networks of Semiconducting Carbon Nanotubes
The
ability to select and enrich semiconducting single-walled carbon nanotubes
(SWNT) with high purity has led to a fast rise of solution-processed
nanotube network field-effect transistors (FETs) with high carrier
mobilities and on/off current ratios. However, it remains an open
question whether it is best to use a network of only one nanotube
species (monochiral) or whether a mix of purely semiconducting nanotubes
but with different bandgaps is sufficient for high performance FETs.
For a range of different polymer-sorted semiconducting SWNT networks,
we demonstrate that a very small amount of narrow bandgap nanotubes
within a dense network of large bandgap nanotubes can dominate the
transport and thus severely limit on-currents and effective carrier
mobility. Using gate-voltage-dependent electroluminescence, we spatially
and spectrally reveal preferential charge transport that does not
depend on nominal network density but on the energy level distribution
within the network and carrier density. On the basis of these results,
we outline rational guidelines for the use of mixed SWNT networks
to obtain high performance FETs while reducing the cost for purification
Polymer-Sorted Semiconducting Carbon Nanotube Networks for High-Performance Ambipolar Field-Effect Transistors
Efficient selection of semiconducting
single-walled carbon nanotubes (SWNTs) from as-grown nanotube samples
is crucial for their application as printable and flexible semiconductors
in field-effect transistors (FETs). In this study, we use atactic
polyÂ(9-dodecyl-9-methyl-fluorene) (a-PF-1-12), a polyfluorene derivative
with asymmetric side-chains, for the selective dispersion of semiconducting
SWNTs with large diameters (>1 nm) from plasma torch-grown SWNTs.
Lowering the molecular weight of the dispersing polymer leads to a
significant improvement of selectivity. Combining dense semiconducting
SWNT networks deposited from an enriched SWNT dispersion with a polymer/metal-oxide
hybrid dielectric enables transistors with balanced ambipolar, contact
resistance-corrected mobilities of up to 50 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup>, low ohmic contact resistance,
steep subthreshold swings (0.12–0.14 V/dec) and high on/off
ratios (10<sup>6</sup>) even for short channel lengths (<10 μm).
These FETs operate at low voltages (<3 V) and show almost no current
hysteresis. The resulting ambipolar complementary-like inverters exhibit
gains up to 61