Organic semiconductor

About: Organic semiconductor is a research topic. Over the lifetime, 15905 publications have been published within this topic receiving 533881 citations.

Electrospun Light-Emitting Nanofibers

Abstract: We have electrospun light-emitting nanofibers from ruthenium(II) tris(bipyridine)/polyethylene oxide mixtures. The electroluminescent fibers were deposited on gold interdigitated electrodes and lit in a nitrogen atmosphere. The fibers showed light emission at low operating voltages (3-4 V), with turn-on voltages approaching the band gap limit of the organic semiconductor. Because of the fiber size, emission from electrospun light-emitting nanofibers is confined to nanoscale dimensions, an attractive feature for sensing applications and lab-on-a-chip integration where highly localized excitation of molecules is required.

Functional organic single crystals for solid-state laser applications

Abstract: Because of long-range order and high chemical purity, organic crystals have exhibit unique properties and attracted a lot of interest for application in solid-state lasers. As optical gain materials, they exhibit high stimulated emission cross section and broad tunable wavelength emission as similar to their amorphous counterpart; moreover, high purity and high order give them superior properties such as low scattering trap densities, high thermal stability, as well as highly polarized emission. As electronic materials, they are potentially able to support high current densities, thus making it possible to realize current driven lasers. This paper mainly describes recent research progress in organic semiconductor laser crystals. The building molecules, crystal growth methods, as well as their stimulated emission characteristics related with crystal structures are introduced; in addition, the current state-of-the-art in the field of crystal laser devices is reviewed. Furthermore, recent advances of crystal lasers at the nanoscale and single crystal light-emitting transistors (LETs) are presented. Finally, an outlook and personal view is provided on the further developments of laser crystals and their applications.

Significant dependence of morphology and charge carrier mobility on substrate surface chemistry in high performance polythiophene semiconductor films

Abstract: The authors report a significant dependence of the morphology and charge carrier mobility of poly(2,5-bis(3-dodecylthiophene-2-yl)thieno[3,2-b]thiophene) (pBTTT) films on the substrate surface chemistry upon heating into its liquid crystal phase. In contrast with films on bare silicon oxide surfaces, pBTTT films on oxide functionalized with octyltrichlorosilane exhibit substantial increases in the lateral dimensions of molecular terraces from nanometers to micrometers, increased orientational order, and higher charge carrier mobility. The large-scale crystallinity of this polymer plays an important role in the high carrier mobility observed in devices, but renders it more sensitive to substrate surface chemistry than other conjugated polymers.

Controllable Molecular Doping and Charge Transport in Solution-Processed Polymer Semiconducting Layers

Abstract: Here, controlled p-type doping of poly(2-methoxy-5-(20-ethylhexyloxy)- pphenylene vinylene) (MEH-PPV) deposited from solution using tetrafluorotetracyanoquinodimethane (F4-TCNQ) as a dopant is presented. By using a co-solvent, aggregation in solution can be prevented and doped films can be deposited. Upon doping the current-voltage characteristics of MEH-PPVbased hole-only devices are increased by several orders of magnitude and a clear Ohmic behavior is observed at low bias. Taking the density dependence of the hole mobility into account the free hole concentration due to doping can be derived. It is found that a molar doping ratio of 1 F4-TCNQ dopant per 600 repeat units of MEH-PPV leads to a free carrier density of 441022m 3. Neglecting the density-dependent mobility would lead to an overestimation of the free hole density by an order of magnitude. The free hole densities are further confirmed by impedance measurements on Schottky diodes based on F4-TCNQ doped MEH-PPV and a silver electrode. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA.

Electronic line-up in light-emitting diodes with alkali-halide/metal cathodes

Abstract: The electronic nature of metal-semiconductor contacts is a fundamental issue in the understanding of semiconductor device physics, because such contacts control charge injection, and therefore play a major role in determining the electron/hole population in the semiconductor itself. This role is particularly important for organic semiconductors as they are generally used in their pristine, undoped form. Here, we review our progress in the understanding of the energy level line-up in finished, blue-emitting, polyfluorene-based light-emitting diodes, which exploit LiF and CsF thin films in combination with Ca and Al to obtain cathodes with low injection barriers. We have used electroabsorption measurements, as they allow the noninvasive determination of the built-in potential when changing the cathode. This provides precious experimental information on the alteration of the polymer/cathode interfacial energy level line-up. The latter is found to depend strongly on the electrode work function. Thus, the Schottky–Mott model for the energy level alignment is found to be a better first-order approximation than those models where strong pinning or large interface dipoles determine the alignment (e.g., Bardeen model), except for electrodes that extensively react with the polymer, and introduce deep gap states. In addition, we show results that validate the approximation of rigid tilting of polymer energy levels with bias (for biases for which no significant injection of carriers occurs). To investigate further the consequences of the electronic line-up on device operation, we complemented the electroabsorption measurements with characterization of the emissive and transport properties of the light-emitting diodes, and confirmed that the cathodic barrier lowering in CsF/Ca/Al and LiF/Ca/Al electrodes leads to the best improvements in electron injection. We found that luminance and overall current are greatly affected by the barrier-reducing cathodes, indicating a truly bipolar transport, with comparable electron and hole currents. We also found significant indications of CsF/Ca/Al cathodes strongly reacting with the polymer, which is suggestive of CsF dissociation and diffusion in the bulk of the polymer.