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Self-Suspended Nanomesh Scaffold for Ultrafast Flexible Photodetectors Based on Organic Semiconducting Crystals
Gvido 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.
Najdeno v: osebi
Ključne besede: nanostrukture, organski polprevodniki, fotonapetostne komponente
Objavljeno: 22.05.2018; Ogledov: 1996; Prenosov: 0
.pdf Polno besedilo (2,52 MB)

The effect of polymer molecular weight on the performance of PTB7-Th:O-IDTBR non-fullerene organic solar cells
Sebastian 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%).
Najdeno v: osebi
Ključne besede: organski polprevodniki, gibljivost, organske sončne celice
Objavljeno: 28.05.2018; Ogledov: 2432; Prenosov: 0
.pdf Polno besedilo (997,85 KB)

Alen Oršulić, 2018, magistrsko delo

Opis: Pričujoče delo obravnava začetne faze rasti organskega polprevodnika N, N´-1H, 1H- perfluorobutil diciano perilen karboksamid (PDIF-CN2) na površini silicijevega dioksida (SiO2). PDIF-CN2 je bil na površino SiO2 nanešen z rotacijskim nanašalcem pod različnimi pogoji. Glede na pogoje nanosa se je spreminjala morfologija narejenih vzorcev. Morfologije so bile analizirane z mikroskopom na atomsko silo. S slik mikroskopa na atomsko silo smo z višinsko porazdelitvijo in funkcijo spektralne gostote moči pridobili podatke o prekritosti vzorcev z otoki molekul PDIF-CN2, višini otokov na površini vzorca, povprečni hrapavosti vzorca, korelacijski dolžini med otoki ter spektralni dolžini in indeksu. Z višinsko porazdelitvijo je bilo ugotovljeno, da znaša povprečna višina otokov na površini vzorcev približno 1,1 nm in da se prekritost vzorcev z molekulami povečuje s povečevanjem koncentracije raztopine in zmanjševanjem kotne hitrosti pri nanosu z rotacijskim nanašalcem. Analiza funkcije spektralne gostote moči površin je pokazala, da je pri večini vzorcev korelacijska dolžina čez celotno preiskano območje, da se povprečna hrapavost povečuje s povečevanjem koncentracije raztopine in kotne hitrosti ter da pospešek pri rotacijskem nanašanju skupaj s kotno hitrostjo vpliva na obliko fraktalov na površini vzorcev.
Najdeno v: osebi
Ključne besede: PDIF-CN2, mikroskop na atomsko silo, rotacijsko nanašanje, Gwyddion, avtokorelacijska funkcija, funkcija spektralne gostote moči.
Objavljeno: 24.09.2018; Ogledov: 2442; Prenosov: 114
.pdf Polno besedilo (2,26 MB)

The role of local potential minima on charge transport in thin organic semiconductor layers
Egon Pavlica, Raveendra Babu Penumala, Bratina Gvido, 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.
Najdeno v: osebi
Ključne besede: Charge transport, Organic semiconductors, Time of flight, Mobility, Traps
Objavljeno: 23.12.2016; Ogledov: 3426; Prenosov: 0
.pdf Polno besedilo (950,46 KB)

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.
Najdeno v: osebi
Ključne besede: organic semiconducotrs, time of flight, transport
Objavljeno: 13.09.2017; Ogledov: 2581; Prenosov: 0
.pdf Polno besedilo (374,71 KB)

Evidence of enhanced photocurrent response in corannulene films
Nadya Patukhova, Layla Martin Samos, Egona 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.
Najdeno v: osebi
Ključne besede: Coranulene, photoconductivity, thin layers, photoexcitation
Objavljeno: 26.09.2017; Ogledov: 2155; Prenosov: 130
.pdf Polno besedilo (644,91 KB)

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