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42.
Evidence of enhanced photocurrent response in corannulene films
Nadya Patukhova, Layla Martin Samos, Egon Pavlica, Gvido Bratina, 2017, izvirni znanstveni članek

Opis: Photoconductivity spectra measured in non-crystalline corannulene thin layers are compared to optical absorption in solution phase and thin films. The unexpected enhanced photoconductivity is correlated with GW–BSE theoretical predictions of corannulene gas-phase excitonic spectra. Theoretical analysis reveals a consistent contribution involving transitions to Super Atomic Molecular Orbitals (SAMOs), a unique set of diffuse orbitals typical of curved conjugated constructs. Results suggest SAMO population via direct photoexcitation as a potential mechanism towards exploiting these diffuse orbitals as conducting channels in suitably assembled quantum nanostructures or solids.
Ključne besede: Coranulene, photoconductivity, thin layers, photoexcitation
Objavljeno v RUNG: 26.09.2017; Ogledov: 3800; Prenosov: 204
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43.
Role of transport band edge variation on delocalized charge transport in high-mobility crystalline organic semiconductors
Gvido Bratina, Andrey Kadashchuk, Egon Pavlica, Fei Tong, 2017, izvirni znanstveni članek

Opis: We demonstrate that the degree of charge delocalization has a strong impact on polarization energy and thereby on the position of the transport band edge in organic semiconductors. This gives rise to long-range potential fluctuations, which govern the electronic transport through delocalized states in organic crystalline layers. This concept is employed to formulate an analytic model that explains a negative field dependence coupled with a positive temperature dependence of the charge mobility observed by a lateral time-of-flight technique in a high-mobility crystalline organic layer. This has important implications for the further understanding of the charge transport via delocalized states in organic semiconductors.
Ključne besede: organic semiconducotrs, time of flight, transport
Objavljeno v RUNG: 13.09.2017; Ogledov: 4213; Prenosov: 0
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44.
Interface-controlled growth of organic semiconductors on graphene
Jinta Mathews, Saim Emin, Egon Pavlica, Matjaž Valant, Gvido Bratina, 2017, izvirni znanstveni članek

Opis: We have studied submonolayer coverages of N,N-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDIF-CN2) on mechanically exfoliated graphene transferred onto SiO2 substrates. Our atomic force microscopy (AFM) data show that PDIF-CN2 forms irregularly-shaped 1.4 nm-high islands. From the selected area diffraction performed with transmission electron microscope (TEM) we conclude that this height corresponds to π−π stacks of molecules, which are inclined for 43° relative to the graphene surface. AFM also showed complete absence of PDIF-CN2 on single-layer graphene (SLG). Electric force microscopy revealed a marked difference in surface charge density between a single-layer graphene and bilayer graphene, with a higher surface charge on SLG than on the bilayer graphene. We associate this behavior with p− type doping of graphene due to the electrostatic dipole induced by the molecular water layer present at the graphene/SiO2 interface. The crucial role of the graphene/SiO2 interface in determining growth of PDIF-CN2 was further confirmed by TEM examination of PDIF-CN2 deposited onto unsupported SLG.
Ključne besede: afm, organic semiconductors, graphene
Objavljeno v RUNG: 18.05.2017; Ogledov: 4757; Prenosov: 0
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46.
The role of local potential minima on charge transport in thin organic semiconductor layers
Egon 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: 5287; Prenosov: 0
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47.
A nanomesh scaffold for supramolecular nanowire optoelectronic devices
Lei Zhang, Egon Pavlica, Gvido Bratina, 2016, izvirni znanstveni članek

Opis: Supramolecular organic nanowires are ideal nanostructures for optoelectronics because they exhibit both efficient exciton generation as a result of their high absorption coefficient and remarkable light sensitivity due to the low number of grain boundaries and high surface-to-volume ratio. To harvest photocurrent directly from supramolecular nanowires it is necessary to wire them up with nanoelectrodes that possess different work functions. However, devising strategies that can connect multiple nanowires at the same time has been challenging. Here, we report a general approach to simultaneously integrate hundreds of supramolecular nanowires of N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) in a hexagonal nanomesh scaffold with asymmetric nanoelectrodes. Optimized PTCDI-C8 nanowire photovoltaic devices exhibit a signal-to-noise ratio approaching 107, a photoresponse time as fast as 10 ns and an external quantum efficiency >55%. This nanomesh scaffold can also be used to investigate the fundamental mechanism of photoelectrical conversion in other low-dimensional semiconducting nanostructures.
Ključne besede: fotodetektor, organski polprevodnik, fotoprevodnost, organski kristal, elektronske komponente, nanožice
Objavljeno v RUNG: 05.10.2016; Ogledov: 5309; Prenosov: 0
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48.
Flexible non-volatile optical memory thin-filmtransistor device with over 256 distinct levelsbased on an organic bicomponent blend
Gvido 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: 5496; Prenosov: 0
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