Nondegenerate continuum model for polymer light-emitting diodes

Davids, P. S.; Saxena, Avadh; Smith, D. L.

doi:10.1063/1.359886

Cited by 71 publications

(37 citation statements)

References 13 publications

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“…Such an explanation has already been reported in the literature, together with the observation of full depletion under reverse bias. [27][28][29] In spite of the high quality of the single crystal under analysis, this contribution cannot be excluded because of the inevitable damage done to the active layer by the deposition of the contact. However, the presence of defects at the metal-organic interface does not directly influence the device rectification properties, which are mostly related to the work function difference of the two electrodes.…”

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confidence: 98%

Organic Metal‐Semiconductor Field‐Effect Transistor (OMESFET) Fabricated on a Rubrene Single Crystal

et al. 2010

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While some applications are becoming a commercial reality, the basics of organic electronic devices still present many unclear aspects.[1] Understanding their mode of operation is not straightforward, because the high density of defects in the active layer generally obscures the intrinsic mechanisms of the devices. However, as in the inorganic case, single crystals of conjugated molecules can be easily grown and efficient, flexible and large-scale devices can be fabricated and characterized. Many of the effects linked to the non-periodicity of the elemental structure and presence of defects can be worked around and issues regarding the intrinsic properties of a device elucidated. Therefore, in order to clarify the operating mechanism of the organic metal-semiconductor field effect transistor (OMESFET), we used rubrene, a well-know organic semiconductor that forms single crystals with an extremely low defect density. [2] An OMESFET is a non-conventional organic field-effect device, already proposed for use as a low-operating-voltage variable resistor, [3][4][5][6][7][8] which differs from the conventional organic field-effect transistor (OFET) by the absence of a gate dielectric. Instead, the gate is directly deposited on the semiconductor layer, on which it forms a blocking contact. This simple architecture requires fewer fabrication steps than a traditional insulated-gate OFET. The device performance depends on the nature of the non-injecting gate metal electrode. Even if its practical integration into complex electronic circuits has still to be demonstrated, its importance for fundamental investigations is obvious, as underlined in a recent paper published during the course of this work. [9] The formation of a metal-organic interface and the injection of electrical charges from a ''non-ohmic'' contact into an organic active layer involve complex and still unresolved processes, [10] and the analysis of these devices, combined with the characterization of single crystal asymmetric diodes, should help in clarifying some of the aspects underlying organic electronics. Besides its importance in many optoelectronic applications, such as solar cells, light emitting diodes, and logic circuits, [11,12] the metalorganic interface is also the basic ingredient of OMESFETs; its analysis is therefore a required preliminary step. From the study of asymmetric metal-semiconductor-metal structures, we did not find any evidence for the formation of a depletion layer in the rubrene single crystal close to the non-ohmic contact. Instead, the dependence of the impedance on the voltage, combined with the analysis of the current-voltage (I-V) characteristics, reveals the effect of a built-in potential, arising from the difference between the work function of the two metal electrodes at both sides of the structure. As long as the diode is under reverse bias, that is, when a negative bias is applied to the high work function electrode, no current flow is registered, while when the system is polarized in forward bias, injection of holes o...

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confidence: 98%

Organic Metal‐Semiconductor Field‐Effect Transistor (OMESFET) Fabricated on a Rubrene Single Crystal

et al. 2010

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“…The potential difference between the electrodes at zero applied bias is called the built-in potential (V BI ). For those devices for which the electrodes work functions lie within the emitting polymer bipolaron gap, [14] and in the absence of pinning and of electric dipoles at polymer/electrode interface(s), eV BI (where e is the electron charge) is equal to the difference of the electrodes work function DW F . Generally, even when the two conditions above are not verified and interfacial dipoles are present V BI can still be expressed in terms of the polymer energy gap (E G ) and of the barrier heights at the polymer electrode interfaces (F B ) according to the following relation: [15] eV…”

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The Built‐In Potential in Blue Polyfluorene‐Based Light‐Emitting Diodes

et al. 2008

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The nature of metal-semiconductor contacts plays a pivotal role in every electronic (and optoelectronic) device, [1] since it controls charge injection into the devices, and, through this, carriers populations, transport regimes, and ultimately, in luminescent devices, the quantum efficiency for conversion of electrons into photons. Such considerations are also true for polymer-based (opto)electronic devices such as PLEDs that show particular promise for cheap fabrication of full-color displays over large areas. A significant effort in this context has been devoted to the development of blue-emitters, [2] that pose the biggest challenge, since the increased energy gap with respect to green and red emitters translates into a greater difficulty in minimizing charge-injection barriers, and in ensuring sufficient stability and durability. Following the success of poly(9,9-dioctylfluorene) as a highly efficient blue emitter, [3] polyfluorene-based homo-and co-polymers (including for example TFB and PFB, see Fig.

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“…39,40 For the case where the organic layer is separated from the metal electrode by a thin insulating barrier, this behavior is interpreted with a model that assumes charge transfer across this barrier. 41,42,43 In this paper we study the dipole formation at interfaces of monolayers of PTCDA (3,4,9,10-perylenetetra-carboxylic-di-anhydride), perylene and benzene molecules adsorbed on close-packed metal surfaces of Au, Ag, Al, Mg and Ca by means of density functional theory (DFT) calculations. We have selected these surfaces because they have a similar and simple structure, as well as a simple electronic (free electron like) structure.…”

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confidence: 99%

First-principles study of the dipole layer formation at metal-organic interfaces

et al. 2010

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We study the dipole layer formed at metal-organic interfaces by means of first-principles calculations. Interface dipoles are monitored by calculating the work function change of Au, Ag, Al, Mg and Ca surfaces upon adsorption of a monolayer of PTCDA (3,4,9,10-perylene-tetra-carboxylic-dianhydride), perylene or benzene molecules. Adsorption of PTCDA leads to pinning of the work function for a range of metal substrates. It gives interface dipoles that compensate for the difference in the clean metal work functions, leading to a nearly constant work function. In contrast, adsorption of benzene always results in a decrease of the work function, which is relatively constant for all metal substrates. Both effects are found in perylene, where adsorption on low work function metals gives work function pinning, whereas adsorption on high work function metals gives work function lowering. The work function changes upon adsorption are analyzed and interpreted in terms of two competing effects. If the molecule and substrate interact weakly, the molecule pushes electrons into the surface, which lowers the work function. If the metal work function is sufficiently low with respect to the unoccupied states of the molecule, electrons are donated into these states, which increases the binding and the work function.

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Nondegenerate continuum model for polymer light-emitting diodes

Cited by 71 publications

References 13 publications

Organic Metal‐Semiconductor Field‐Effect Transistor (OMESFET) Fabricated on a Rubrene Single Crystal

Organic Metal‐Semiconductor Field‐Effect Transistor (OMESFET) Fabricated on a Rubrene Single Crystal

The Built‐In Potential in Blue Polyfluorene‐Based Light‐Emitting Diodes

First-principles study of the dipole layer formation at metal-organic interfaces

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