Nonlinear transport in semiconducting polymers at high carrier densities

Yuen, Jonathan D.; Menon, Reghu; Coates, Nelson E.; Namdas, Ebinazar B.; Cho, Shinuk; Hannahs, S. T.; Moses, D.; Heeger, Alan J.

doi:10.1038/nmat2470

Cited by 104 publications

(104 citation statements)

References 18 publications

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“…These results indicate that PF or Schottky mechanisms may be valid above 200 K for d ≥ 16 nm, where a voltage-dependent E a is observed (Table 1). PF transport has been proposed for organic semiconductors across distances greater than studied here, and is consistent with observed E dependence (46)(47)(48)(49).…”

Section: Resultssupporting

confidence: 89%

“…Given that classical mechanisms are not consistent with the BTB JV behavior, we note a few recent observations of field-driven mechanisms for transport in much thicker organic films (>100 nm) (46)(47)(48)(49). Whereas transport dimensions and bias voltages were much larger than the 4.5-22-nm range studied here, a linear dependence of ln J vs. E 1/2 was observed, as was T-independent conductance at low T. Although the mechanism is controversial, these observations were attributed to field-assisted hopping (46,48), field-assisted tunneling (47,48), multistep tunneling (47), or behavior similar to a Luttinger liquid (49). For the case of polythiophene thin-film transistors, a transition from PF-like behavior at room temperature to temperature-independent fieldemission hopping with an E 1/2 dependence at low temperature was reported (48).…”

Section: Resultsmentioning

confidence: 78%

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Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions

Yan

Bergren

McCreery

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

160

259

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In this work, we bridge the gap between short-range tunneling in molecular junctions and activated hopping in bulk organic films, and greatly extend the distance range of charge transport in molecular electronic devices. Three distinct transport mechanisms were observed for 4.5-22-nm-thick oligo(thiophene) layers between carbon contacts, with tunneling operative when d < 8 nm, activated hopping when d > 16 nm for high temperatures and low bias, and a third mechanism consistent with field-induced ionization of highest occupied molecular orbitals or interface states to generate charge carriers when d = 8-22 nm. Transport in the 8-22-nm range is weakly temperature dependent, with a field-dependent activation barrier that becomes negligible at moderate bias. We thus report here a unique, activationless transport mechanism, operative over 8-22-nm distances without involving hopping, which severely limits carrier mobility and device lifetime in organic semiconductors. Charge transport in molecular electronic junctions can thus be effective for transport distances significantly greater than the 1-5 nm associated with quantum-mechanical tunneling.all-carbon molecular junction | attenuation coefficient | field ionization | strong electronic coupling C harge transport mechanisms in organic and molecular electronics underlie the ultimate functionality of a new generation of electronic devices. Understanding, controlling, and designing molecular devices for use as practical components requires an intimate knowledge of the system energy levels and operative transport mechanisms, and how key variables such as molecule length, identity, temperature, etc., affect device performance parameters. Especially interesting in this context is the relationship between organic electronic devices, which typically have active layer thicknesses of tens to hundreds of nanometers, and molecular electronic devices reported to date, in which at least one dimension for charge propagation is below 10 nm. Indeed, many types of functional organic electronic devices have been demonstrated, including thinfilm transistors, organic light-emitting diodes, and memory cells (1, 2). Bridging the gap between organic and molecular devices may therefore reveal pathways for improving the performance of such devices, or even lead to new types of devices based on alternative transport mechanisms.The great majority of molecular electronic devices investigated to date have transport distances of <5 nm between the contacts, where the prevalent transport mechanism is quantum-mechanical tunneling. For this distance range, there is general agreement that the conductance scales exponentially with length, with an attenuation coefficient (β), defined as the slope of ln J vs. thickness (d), equal to 8 to 9 nm −1 for aliphatic molecules (3-6) and 2-3 nm −1 for aromatic molecules (7)(8)(9)(10)(11)(12)(13)(14). A few molecular electronic systems have been investigated beyond 5 nm (15, 16), some of which exhibit a decrease in β to less than 1 nm −1 . Such small values of β ar...

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Section: Resultssupporting

confidence: 89%

Section: Resultsmentioning

confidence: 78%

Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions

Yan

Bergren

McCreery

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

160

259

View full text Add to dashboard Cite

show abstract

“…Numerous experiments, however, have shown that the conductivity at low temperatures is finite [2][3][4][5][6] . The breakdown of the semi-classical approaches at low temperatures is due to quantum mechanical zero-point energy of the system.…”

Section: Resultsmentioning

confidence: 99%

Polaron hopping mediated by nuclear tunnelling in semiconducting polymers at high carrier density

et al. 2013

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The transition rate for a single hop of a charge carrier in a semiconducting polymer is assumed to be thermally activated. As the temperature approaches absolute zero, the predicted conductivity becomes infinitesimal in contrast to the measured finite conductivity. Here we present a uniform description of charge transport in semiconducting polymers, including the existence of absolute-zero ground-state oscillations that allow nuclear tunnelling through classical barriers. The resulting expression for the macroscopic current shows a power-law dependence on both temperature and voltage. To suppress the omnipresent disorder, the predictions are experimentally verified in semiconducting polymers at high carrier density using chemically doped in-plane diodes and ferroelectric field-effect transistors. The renormalized current-voltage characteristics of various polymers and devices at all temperatures collapse on a single universal curve, thereby demonstrating the relevance of nuclear tunnelling for organic electronic devices.

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“…Recent results have included the realization of high carrier mobilities approaching 1 cm 2 /Vs in semicrystalline films of poly(2,5-bis(3-alkylthiophen-2-yl)thieno(3,2-b)thiophene) (pBTTT) 1 and the observation of nonlinear, metallic transport at high carrier concentrations 2 which can be described in terms of a one-dimensional Luttinger liquid 3 . Charge transport is usually probed by electrical measurements over a length scale of several micrometers using field-effect transistor (FET) structures.…”

mentioning

confidence: 99%

Local Charge Trapping in Conjugated Polymers Resolved by Scanning Kelvin Probe Microscopy

et al. 2009

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Nonlinear transport in semiconducting polymers at high carrier densities

Cited by 104 publications

References 18 publications

Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions

Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions

Polaron hopping mediated by nuclear tunnelling in semiconducting polymers at high carrier density

Local Charge Trapping in Conjugated Polymers Resolved by Scanning Kelvin Probe Microscopy

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