31. The effect of polymer molecular weight on the performance of PTB7-Th:O-IDTBR non-fullerene organic solar cellsSebastian F. Hoefler, Egon Pavlica, Gvido Bratina, 2018, izvirni znanstveni članek Opis: Recent advances in the development of non-fullerene acceptors have increased the power conversion efficiency of organic solar cells to approximately 13%. Fullerene-derivatives and non-fullerene acceptors possess distinctively different structural, optical and electronic properties, which also change the requirements on the polymer donor in non-fullerene organic solar cells. Therefore, in this study, the effect of the molecular weight of the conjugated polymer on the photovoltaic performance, charge carrier mobility, crystallization properties, film morphology, and non-geminate recombination dynamics is systematically investigated in polymer:small molecule organic solar cells using the low bandgap polymer PTB7-Th as the donor and the non-fullerene indacenodithiophene-based small molecule O-IDTBR as the acceptor. Among the examined polymer samples (50–300 kDa), high molecular weights of PTB7-Th (with an optimum molecular weight of 200 kDa) are advantageous to achieve high efficiencies up to 10%, which can be correlated with an increased crystallinity, an improved field-effect hole mobility (1.05 × 10−2 cm2 V−1 s−1), lower charge carrier trapping and a reduced activation energy of charge transport (98 meV). Bias-assisted charge extraction and transient photovoltage measurements reveal higher carrier concentrations (1016 cm−3) and long lifetimes (4.5 μs) as well as lower non-geminate recombination rate constants in the corresponding devices, supporting the high photocurrents (ca. 15.2 mA cm−2) and fill factors (>60%). Ključne besede: organski polprevodniki, gibljivost, organske sončne celice Objavljeno v RUNG: 28.05.2018; Ogledov: 4486; Prenosov: 0 Gradivo ima več datotek! Več... |
32. Self-Suspended Nanomesh Scaffold for Ultrafast Flexible Photodetectors Based on Organic Semiconducting CrystalsGvido Bratina, Egon Pavlica, 2018, izvirni znanstveni članek Opis: Self-standing nanostructures are of fundamental interest in materials sci- ence and nanoscience and are widely used in (opto-)electronic and photonic devices as well as in micro-electromechanical systems. To date, large-area and self-standing nanoelectrode arrays assembled on flexible substrates
have not been reported. Here the fabrication of a hollow nanomesh scaffold on glass and plastic substrates with a large surface area over 1 mm2 and ultralow leakage current density (≈1–10 pA mm−2 @ 2 V) across the empty scaffold is demonstrated. Thanks to the continuous sub-micrometer space formed in between the nanomesh and the bottom electrode, highly crystalline and dendritic domains of 6,13-bis(triisopropylsilylethinyl)pentacene growing within the hollow cavity can be observed. The high degree of order at the supramolecular level leads to efficient charge and exciton transport; the pho- tovoltaic detector supported on flexible polyethylene terephthalate substrates exhibits an ultrafast photoresponse time as short as 8 ns and a signal-to- noise ratio approaching 105. Such a hollow scaffold holds great potential as a novel device architecture toward flexible (opto-)electronic applications based on self-assembled micro/nanocrystals. Ključne besede: nanostrukture, organski polprevodniki, fotonapetostne komponente Objavljeno v RUNG: 22.05.2018; Ogledov: 3681; Prenosov: 0 Gradivo ima več datotek! Več... |
33. Negative field‐dependent charge mobility in crystalline organic semiconductors with delocalized transportFei Tong, Andrey Kadashchuk, Egon Pavlica, Gvido Bratina, 2018, izvirni znanstveni članek Opis: Charge-carrier mobility has been investigated by time-of-flight (TOF) transient photocurrent in a lateral transport con- figuration in highly crystalline thin films of 2,7-dioctyl[1]benzothieno [3,2-b][1] benzothiophene (C8-BTBT) grown by a zone-casting alignment technique. High TOF mobility has been revealed that it is consistent with the delocalized nature of the charge transport in this material, yet it featured a positive temperature dependence at T ≥ 295 K. Moreover, the mobility was surprisingly found to decrease with electric field in the high-temperature region. These observations are not compat- ible with the conventional band-transport mechanism. We have elaborated an analytic model based on effective-medium approximation to rationalize the puzzling findings. The model considers the delocalized charge transport within the energy landscape formed by long-range transport band-edge variations in imperfect organic crystalline materials and accounts for the field-dependent effective dimensionality of charge transport percolative paths. The results of the model calculations are found to be in good agreement with experimental data. Ključne besede: time of flight, organic semiconductors, single crystals Objavljeno v RUNG: 07.05.2018; Ogledov: 5371; Prenosov: 0 Gradivo ima več datotek! Več... |
34. Univerza v Novi Gorici, Spremljanje, ugotavljanje in zagotavljanje kakovosti, Poročilo za študijsko leto 2013/2014Iztok Arčon, Martina Bergant Marušič, Aleš Bogovič, Lorena Butinar, Gvido Bratina, IMRE CIKAJLO, Saša Dobričić, Elsa Fabbretti, Mladen Franko, Renata Kop, Urška Lavrenčič Štangar, Martin Knez, Katja Mihurko, Jana Laganis, Branka Mozetič Vodopivec, Egon Pavlica, Ingrid Petrič, Samo Stanič, Tea Stibilj Nemec, Arthur Stepanov, Boštjan Potokar, Veronika Piccinini, Peter Purg, Aljaž Rener, Nives Štefančič, Ana Toroš, Tanja Urbančič, Vanesa Valentinčič, Aleš Vaupotič, Sabina Zelinšček, 2014, elaborat, predštudija, študija Ključne besede: zagotavljanje kakovosti, visoko šolstvo, univerza Objavljeno v RUNG: 05.02.2018; Ogledov: 4320; Prenosov: 0 Gradivo ima več datotek! Več... |
35. Evidence of enhanced photocurrent response in corannulene filmsNadya 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: 3958; Prenosov: 204 Celotno besedilo (644,91 KB) |
36. |
37. |
38. Interface-controlled growth of organic semiconductors on grapheneJinta 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: 4898; Prenosov: 0 Gradivo ima več datotek! Več... |
39. Fast-Response Photonic Device Based on Organic-Crystal Heterojunctions Assembled into a Vertical-Yet-Open Asymmetric ArchitectureLei Zhang, Egon Pavlica, Zhong, Xiaolan, Liscio Fabiola, LI Songlin, Gvido Bratina, Orgiu Emanuele, Samori Paolo, 2017, izvirni znanstveni članek Ključne besede: organski polprevodniki, merjenja časa preleta, organski fotodetektorji Objavljeno v RUNG: 24.01.2017; Ogledov: 4287; Prenosov: 0 Gradivo ima več datotek! Več... |
40. 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: 5463; Prenosov: 0 Gradivo ima več datotek! Več... |