Understanding Charge Transport in Mixed Networks of Semiconducting Carbon Nanotubes

Abstract

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.

Semiconducting Single‐Walled Carbon Nanotubes or Very Rigid Conjugated Polymers: A Comparison

“…[109][110][111] More large-scale approaches include alignment by flow in microchannels, [112,113] evaporation-driven self-assembly at a meniscus [114,115] or dose-controlled, floating evaporative selfassembly and alignment (FESA), [116,117] stretching of random films and subsequent transfer, [118] the application of shear to lyotropic nanotube dispersions, [88,119] and alignment by very slow filtration. For individual devices and small numbers of nanotubes between electrodes, alignment by applying an AC or DC electric field during deposition from dispersion is a possibility.…”

“…The P3HT chains can order into 2D π-stacked lamella with weakly interacting H-aggregate states as the only emissive species causing a significant redshift in Adv. [111] Copyright 2016, American Chemical Society. Mater.…”

Assembly and Electronic Applications of Colloidal Nanomaterials

“…These two types of FET are incorporated in different circuit designs for specific functions. [44][45][46] Minimal hysteresis is another important factor when evaluating electronic materials for FETs. [21,43] Depletion or enhancement operation modes can be realized through the control and tuning of V T and subthreshold swing (i.e., the inverse slope of log(I d ) versus V g in Figure 1B).…”

“…[338] Charge transport is also affected by the purity of semiconducting SWCNTs. [46] Furthermore, similar to nanocrystal solids, residual surfactants at tube-tube contacts reduce the intertube coupling, which implies that their Reproduced with permission. [344] Polydispersity in the chirality of semiconducting SWCNTs can also introduce problems since SWCNTs with narrower bandgaps tend to dominate charge transport in networks, which can limit on-currents and effective carrier mobility.…”

“…[347,348] The gate coupling can be rigorously determined by including the effects of the SWCNT quantum capacitance and intertube coupling. [46] Low hysteresis and air stability of SWCNT FETs are also essential to the design, fabrication, and operation of large-scale integrated circuits. [36] Quantitative analysis shows that the intrinsic gate capacitance increases with increasing SWCNT density, and gradually approaches the dielectric capacitance defined by the parallel-plate model.…”