Control mechanisms for transport and nonlinear optical response in organic materials: a tale of twists and barriers

Facchetti, Antonio; Hutchison, Geoffrey; Keinan, Shahar; Ratner, Mark A.

doi:10.1016/j.ica.2004.06.061

Cited by 8 publications

(9 citation statements)

References 66 publications

(41 reference statements)

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“…As stated earlier, this presents the opportunity to directly compare the results from these computational studies (with no free parameters) with experimentally obtained results to directly validate the variable-range hopping model. The use of first principles quantum chemistry, in particular, density functional theory, to calculate the parameters of k et and use them to explain experimental charge transport results has been demonstrated in the literature …”

Section: Methodsmentioning

confidence: 99%

Charge Transport in Imperfect Organic Field Effect Transistors: Effects of Explicit Defects and Electrostatics

2010

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The effects of defects and electrostatics on charge transport in realistic organic field effect transistors were studied using a combination of first principles quantum chemistry calculations and Monte Carlo simulations with explicit introduction of defect sites. The results show that electrostatic interactions dramatically affect the field and carrier concentration dependence of charge transport in devices that include a significant number of traps, as well as its “switch-on” characteristics. Our results also show that charge transport decreases linearly as a function of neutral defect concentration as conduction pathways are turned off. For charged defects, mobility of imperfect devices is lower relative to defect-free devices but is surprisingly unaffected by the concentration of charged defects. The exact statistics of electrostatic disorder introduced by charged defects is found to obey a Poisson distribution rather than Gaussian or exponential as previously assumed. We also demonstrate that without including electrostatic interactions, simulations of transistors exhibit an unphysical negative differential resistance at higher defect levels.

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Section: Methodsmentioning

confidence: 99%

Charge Transport in Imperfect Organic Field Effect Transistors: Effects of Explicit Defects and Electrostatics

2010

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“…Previous work has shown that materials with large (hyper)polarizabilities generally exhibit significantly higher dielectric responses than other molecular materials. 21,39,40 In this regard, electron-donating and electron-accepting moieties are known to enhance molecular (hyper)polarizabilities when introduced in tandem to conjugated π-systems. 41−44 These molecular materials, commonly referred to as DBA materials ( Figure 1) have inspired significant research in the scientific community for implementation in nonlinear optics, 44−47 charge transfer, 48−50 and charge transport.…”

Section: ■ Introductionmentioning

confidence: 99%

Molecular Donor–Bridge–Acceptor Strategies for High-Capacitance Organic Dielectric Materials

Marks

Ratner

2015

J. Am. Chem. Soc.

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Donor-bridge-acceptor (DBA) systems occupy a rich history in molecular electronics and photonics. A key property of DBA materials is their typically large and tunable (hyper)polarizabilities. While traditionally, classical descriptions such as the Clausius-Mossotti formalism have been used to relate molecular polarizabilities to bulk dielectric response, recent work has shown that these classical equations are inadequate for numerous materials classes. Creating high-dielectric organic materials is critically important for utilizing unconventional semiconductors in electronic circuitry. Employing a plane-wave density functional theory formalism, we investigate the dielectric response of highly polarizable DBA molecule-based thin films. Such films are found to have large dielectric response arising from cooperative effects between donor and acceptor units when mediated by a conjugated bridge. Moreover, the dielectric response can be systematically tuned by altering the building block donor, acceptor, or bridge structures and is found to be nonlinearly dependent on electric field strength. The computed dielectric constants are largely independent of the density functional employed, and qualitative trends are readily evident. Remarkably large computed dielectric constants >15.0 and capacitances >6.0 μF/cm(2) are achieved for squaraine monolayers, significantly higher than in traditional organic dielectrics. Such calculations should provide a guide for designing high-capacitance organic dielectrics that should greatly enhance transistor performance.

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“…8,[48][49][50] In other cases, such as twisted chromophores the situation is more complex. 49,51,52 The important observation is that further improvements of molecular first hyperpolarizability can be expected and the realization of electro-optic activity on the order of 1000 pm/V is likely an achievable goal.…”

Section: Optimizing Chromophore Molecular First Hyperpolarizability βmentioning

confidence: 99%

Optimizing electro-optic activity in chromophore/polymer composites and in organic chromophore glasses

et al. 2005

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The motivation for use of organic electro-optic materials derives from (1) the inherently fast (sub-picosecond) response of π-electron systems in these materials to electrical perturbation making possible device applications with gigahertz and terahertz bandwidths, (2) the potential for exceptionally large (e.g., 1000 pm/V) electro-optic coefficients that would make possible devices operating with millivolt drive voltages, (3) light weight, which is a concern for satellite applications, and (4) versatile processability that permits rapid fabrication of a wide variety of devices including conformal and flexible devices, three dimensional active optical circuitry, hybrid organic/silicon photonic circuitry, and optical circuitry directly integrated with semiconductor VLSI electronics. The most significant concerns associated with the use of organic electro-optic materials relate to thermal and photochemical stability, although materials with glass transition temperatures on the order of 200°C have been demonstrated and photostability necessary for long term operation at telecommunication power levels has been realized. This communication focuses on explaining the theoretical paradigms that have permitted electro-optic coefficients greater than 300 pm/V (at telecommunication wavelengths) to be achieved and on explaining likely improvements in electro-optic activity that will be realized in the next 1-2 years. Systematic modifications of materials to improve thermal and photochemical stability are also discussed.

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Control mechanisms for transport and nonlinear optical response in organic materials: a tale of twists and barriers

Cited by 8 publications

References 66 publications

Charge Transport in Imperfect Organic Field Effect Transistors: Effects of Explicit Defects and Electrostatics

Charge Transport in Imperfect Organic Field Effect Transistors: Effects of Explicit Defects and Electrostatics

Molecular Donor–Bridge–Acceptor Strategies for High-Capacitance Organic Dielectric Materials

Optimizing electro-optic activity in chromophore/polymer composites and in organic chromophore glasses

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