91. The role of local potential minima on charge transport in thin organic semiconductor layersEgon Pavlica, Raveendra Babu Penumala, Gvido Bratina, 2016, izvirni znanstveni članek Opis: We have performed a systematic study of dependence of time-resolved photocurrent on the point of charge excitation within the organic semiconductor channel formed by two coplanar metal electrodes. The results confirm that spatial variation of electric field between the electrodes crucially determines transport of photogenerated charge carriers through the organic layer. Time-of-flight measurements of photocurrent demonstrate that the transit time of photogenerated charge carrier packets drifting between the two electrodes decreases with increasing travelling distance. Such counterintuitive result cannot be reconciled with the spatial distribution of electric field between coplanar electrodes, alone. It is also in contrast to expected role of space-charge screening of external electric field. Supported by Monte Carlo simulations of hopping transport in disordered organic semiconductor layer, we submit that the space-charge screens the external electric field and captures slower charge carriers from the photogenerated charge carrier packet. The remaining faster carriers, exhibit velocity distribution with significantly higher mean value and shorter transit time.
Ključne besede: Charge transport, Organic semiconductors, Time of flight, Mobility, Traps
Objavljeno v RUNG: 23.12.2016; Ogledov: 5375; Prenosov: 0
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92. THE MORPHOLOGY DEPENDENCE ON GROWTH PARAMETERS IN NANOSTRUCTURED SEMICONDUCTORSMiha Gunde, 2014, diplomsko delo Opis: Poly(3-hexylthiophene) (P3HT) is an organic semiconductor material that is widely studied in the photovoltaics and transistor fields of research. The polymer exhibits a relatively high charge carrier mobility when the molecules are ordered in a crystalline way. In this
case the material exhibits a fibril-like morphology, which is usually studied by atomic force microscopy (AFM). Previous studies show that blending P3HT with graphene can further improve the charge carrier transport properties of the film. In this experiment, the scanning electron microscope (SEM) has been chosen, due to its practical aspects such as speed of operation and ease of use. Three sets of samples have been analyzed, containing films made of P3HT+graphene blends at different concentrations. The aims of the experiment are:
i) to find good conditions for the observation of the morphology features of the film
ii) to perform a morphological analysis of the surface of three sets of samples containing both pure P3HT, and P3HT+graphene blend, and possibly to highlight correlation between morpholgy and the charge transport properties.
Surface analysis is done by detecting the secondary electron (SE) emission, which is sensitive to topographical features of the surface. Good observation conditions were established by coating the specimen with a thin layer of conductive coating, using a high energy beam (30 keV), and tilting the sample to an angle (30 ◦ ). In two out of three of the analyzed pure P3HT films, the presence of fibrilles indicated a possibly good charge mobility, which has
been confirmed by electrical measurements using time-of-flight photoconductivity method (TOF). The presence of graphene has only slightly modified morphology of the film. Features of graphene flakes, which lie flat in the film, have been observed such as flake edges and folds. The flakes are homogeneously dispersed in the film without forming any connected network. TOF measurements have shown an increase in mobility of the charge carriers in the P3HT+graphene film.
Ključne besede: scanning electron microscope, organic semiconductor thin film, P3HT, graphene, morphology
Objavljeno v RUNG: 01.12.2016; Ogledov: 6510; Prenosov: 168
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93. Flexible non-volatile optical memory thin-filmtransistor device with over 256 distinct levelsbased on an organic bicomponent blendGvido Bratina, Egon Pavlica, 2016, izvirni znanstveni članek Opis: Flexible non-volatile optical memory thin-filmtransistor device with over 256 distinct levelsbased on an organic bicomponent blendTim Leydecker1, Martin Herder2, Egon Pavlica3,GvidoBratina3,StefanHecht2*, Emanuele Orgiu1*and Paolo Samorì1*Organic nanomaterials are attracting a great deal of interest for use in flexible electronic applications such as logiccircuits, displays and solar cells. These technologies have already demonstrated good performances, but flexible organicmemories are yet to deliver on all their promise in terms of volatility, operational voltage, write/erase speed, as well asthe number of distinct attainable levels. Here, we report a multilevel non-volatile flexible optical memory thin-filmtransistor based on a blend of a reference polymer semiconductor, namely poly(3-hexylthiophene), and a photochromicdiarylethene, switched with ultraviolet and green light irradiation. A three-terminal device featuring over 256 (8 bitstorage) distinct current levels was fabricated, the memory states of which could be switched with 3 ns laser pulses.We also report robustness over 70 write–erase cycles and non-volatility exceeding 500 days. The device was implementedon a flexible polyethylene terephthalate substrate, validating the concept for integration into wearable electronics andsmart nanodevices.
Ključne besede: organic semiconductors
time of flight
Objavljeno v RUNG: 22.06.2016; Ogledov: 5568; Prenosov: 0
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95. Electrical conductivity in 3,4,9,10-perylenetetracarboxylic dianhidride (PTCDA)Gvido Bratina, Robert Hudej, Marko Zavrtanik, John Nimly Brownell, 2001, izvirni znanstveni članek Opis: The transient photoresponse in 3,4,9,10-perylenetetracarboxylic dianhydride was examined in metal/organic semiconductor/metal heterostructures. Electron-hole pairs are generated within the structure for fields higher than 5 X 10[sup]4 V/cm as a consequence of the exciton dissociation. The mobility of the electrons perpendicular to the molecular layers increases with the applied electric field and saturates for fields higher than 5 X 10[sup]4 V/cm.
Ključne besede: organic semiconductor, thin films, transient photoconductivity
Objavljeno v RUNG: 10.07.2015; Ogledov: 6602; Prenosov: 40
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96. The impact of gravel extraction on hyporheic ecology: a case study of the Bača river (W Slovenia) : dissertationNataša Mori, 2008, doktorska disertacija Ključne besede: hyporheic invertebrate, Soča river, Bača river, hyporheic biota, benthic organisms, particulate organic matter, POM, fine sediment, ETS activity, electron transport system, sediments, Nematoda, Harpacticoida, Chironomidae, gravel extraction, environmental impact assessment
Objavljeno v RUNG: 19.02.2015; Ogledov: 5405; Prenosov: 389
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