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1.
  • Arias, A.C., et al. (författare)
  • Use of tin oxide thin films as a transparent electrode in PPV based light-emitting diodes
  • 2000
  • Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 371:1, s. 201-206
  • Tidskriftsartikel (refereegranskat)abstract
    • Tin oxide (TO) thin films, nominally undoped, have been used as electrodes in poly(p-phenylene vinylene) (PPV) based organic electroluminescent devices. The evolution of the crystallinity and the electrical resistance of TO films submitted to the PPV thermal conversion conditions, have been investigated. It has been found that the electrical resistance is decreased whereas the crystallinity of the film is increased. It is shown in this work, that the photoluminescence of PPV converted on top of TO substrates is not as quenched as it is when converted on top of indium-tin oxide (ITO) substrates. The quantum efficiency of light-emitting diode is 0.07% at 17 V forward bias. It is also shown that the work function of TO films is very stable to different cleaning procedures, in contrast with previous results obtained for ITO films.
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2.
  • Baroni, Mpma, et al. (författare)
  • Modeling and gradient pattern analysis of irregular SFM structures of porous silicon
  • 2006
  • Ingår i: Microelectronics Journal. - : Elsevier BV. - 0026-2692. ; 37:4, s. 290-294
  • Tidskriftsartikel (refereegranskat)abstract
    • Technological applications in opto-electronic devices have increased the interest in characterizing porous silicon structure patterns. Due to its physical properties, solutions from KPZ 2D are adopted to simulate the structure of porous material interface whose spatial characteristics are equivalent to those found in porous silicon samples. The analysis of the simulated and real scanning Force Microscopy (SFM) surfaces was done using the Gradient Pattern Analysis (GPA). We found that the KPZ 2D model presented asymmetry levels compatible with the irregular surfaces observed by means of SFM images of pi-Si.
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3.
  • Baroni, M. P. M. A., et al. (författare)
  • Optical and morphological properties of porous diamond-like-carbon films deposited by magnetron sputtering
  • 2006
  • Ingår i: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093 .- 1873-4812. ; 352:32-35, s. 3734-3738
  • Tidskriftsartikel (refereegranskat)abstract
    • Porous diamond-like-carbon (PDLC) thin films obtained on silicon substrate by DC low energy magnetron sputtering have been investigated by photoluminescence, transmission and reflection spectroscopy, photoacoustic and spectroscopic ellipsometry. The absorption features observed for these films show similarities with those of porous silicon (PS) as well as in the performed gradient structural pattern classification of the SFM porosity, by means of the computational GPA-flyby environment on PS and PDLC samples. The dielectric function is also calculated for the bulk diamond-like carbon using the full-potential linearized augmented plane wave method within the framework of local density approximation to density functional theory. From the measurement a low real dielectric constant of about 4.5 at 0.8 eV was found whereas the calculated e(1)(0) for the bulk diamond has a value of 5.5.
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4.
  • Benatto, L., et al. (författare)
  • Comparing C-60 and C-70 as acceptor in organic solar cells : Influence of the electronic structure and aggregation size on the photovoltaic characteristics
  • 2020
  • Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 697
  • Tidskriftsartikel (refereegranskat)abstract
    • The difference in aggregation size of the C-60 and C-70 fullerenes affect the photovoltaic performance of devices assembled in the so-called bilayer architecture with poly [2,7-(9,9- dioctyl- dibenzosilole)- alt-4,7- bis(thiophen-2-yl)benzo- 2,1,3- thiadiazole] (PSiF-DBT) as the electron donor material. Despite the better performance of the C-70 devices, which is related to the high absorption coefficient in the visible range and the superior charge transport properties, the short-circuit current variation upon annealing treatment at 100 degrees C is approximately twice bigger when the C-60 is the acceptor. We attribute this effect to the tendency of C-60 in form smaller aggregate domains relatively to the C-70. The increased roughness on the polymeric surface after annealing results in an enhanced donor/acceptor contact area and assists the fullerene diffusion deeper inside the polymeric layer. This effect leads to a better mixing between donor and acceptor species and create a interpenetrating layer close to the so-called bulk heterojunction. Since C-60 forms smaller aggregates, this mechanism is more pronounced for this molecule. Therefore, a significant variation in the performance of the C-60 devices is observed after this kind of treatment. Density Functional Theory calculations of the potential energy of interaction between two fullerene molecules and X-Ray measurements gives evidences to support this idea. In addition, combining spectrally resolved external quantum efficiency measurements with optical modeling our results also indicate the occurrence of the bilayer interfacial mixing for PSiF-DBT/C-60.
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5.
  • Benatto, L., et al. (författare)
  • Understanding the effect of solvent additive in polymeric thin film : turning a bilayer into a bulk heterojunction-like photovoltaic device
  • 2020
  • Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 53:36
  • Tidskriftsartikel (refereegranskat)abstract
    • Here we report the effect of an additive solvent, 1,8-diiodooctane (DIO), on the performance of a bilayer organic photovoltaic device in which the active layer comprises poly[2,7-(9,9-bis(2 ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PSiF-DBT) as the electron donor material and C60 as the electron acceptor material. We observed that when the donor layer was treated with 1% of DIO the power conversion efficiency (PCE) of the device increased by 138.4% in relation to the device with an untreated donor layer, and 21.3% in relation to the device containing a donor layer submitted to thermal annealing. The main effects that lead to this increase in PCE are the large interfacial area between donor and acceptor materials and the improved conductivity at low voltages. The increase in polymer surface roughness leads to a more effective PSiF-DBT/C60 interface for exciton dissociation. This effect, as well as the increase in the conductivity, raised the short circuit current density (JSC) to 13.89 mA cm−2 and the PCE to 4.84%. Our conclusions are supported by morphological analysis, chemical cross-sectional evaluations with advanced microscopy techniques, charge mobility measurements, as well as by theoretical simulations of the devices in which the changes on the donor/acceptor interfacial area were considered. The outcomes suggest that solvent additives could be an alternative treatment to replace the thermal annealing, which imposes further difficulties in performing lab-to-manufacturing upscaling.
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6.
  • Da, Silva A.F., et al. (författare)
  • Asymmetric nonlinear amplitude in patterns of porous silicon
  • 2000
  • Ingår i: Physica A. - 0378-4371 .- 1873-2119. ; 283:1, s. 223-227
  • Tidskriftsartikel (refereegranskat)abstract
    • A gradient pattern analysis is used to report a phenomenogical evidence of asymmetric nonlinear spatial distribution of porous silicon structures. We used a canonical sample set obtained from scanning force microscopy. Due to the high sensitivity of the gradient field operator, it is possible to correlate the photoluminescence performance of porous silicon with different degree of asymmetries and spatial nonlinearity. A generalization of this new approach to quantify nonlinear amplitude fragmentation in complex lattices is proposed.
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7.
  • da Silva, A. Ferreira, et al. (författare)
  • Growth, Electrical and Optical Properties of SnO2:F on ZnO, Si and Porous Si Structures
  • 2009
  • Ingår i: NANOTECH CONFERENCE & EXPO 2009, VOL 1, TECHNICAL PROCEEDINGS. - : CRC PRESS-TAYLOR & FRANCIS GROUP. - 9781439817827 ; , s. 352-
  • Konferensbidrag (refereegranskat)abstract
    • In this work we have analyzed the optical absorption of the ZnO and SnO2:F (FTO) films and applied them in porous silicon light-emitting diodes. The absorption and energy gap were calculated by employing the projector augmented wave method [1] within the local density approximation and with a modeled on-site self-interaction-like correction potential within the LDA+U-S/C [2]. Experiment and theory show a good agreement when the optical absorption and optical energy gap are considered. A layer of FTO is deposited by spray pyrolysis on top of porous Si (PSi) or ZnO/(PSi) in order to make the LEDs. The morphology and roughness of the films are analyzed by Atomic Force Microscopy before and after the FTO deposition. The electrical and optical properties are studied by characteristics curves J x V, and electroluminescence intensity versus bias.
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8.
  • Ding, L., et al. (författare)
  • Photovoltaic cells with a conjugated polyelectrolyte
  • 2000
  • Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 110:2, s. 133-140
  • Tidskriftsartikel (refereegranskat)abstract
    • We describe photovoltaic cells made from a novel conjugated polyelectrolyte, the lithium salt of poly(thiophene-3-acetic acid) (PTAA-Li). The aqueous solubility of this polyelectrolyte allows formation of blend electrodes with a dispersion of the metallic polymer Poly(Ethylene DiOxyThiophene) (PEDOT). The incident monochromatic photon to current conversion efficiency (IPCE) of the cells were improved up to 19% by blending PTAA-Li with PEDOT to modify the ITO electrode, in combination with the low bandgap polymer poly(3-(4-octylphenyl)thiophene) (POPT), and C60 as electron acceptor. We attribute the increase of efficiency to the improved contact area between the conjugated polyelectrolyte and PEDOT.
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9.
  • Ferreira, Da Silva A., et al. (författare)
  • Characterization of asymmetric fragmentation patterns in SFM images of porous silicon
  • 2000
  • Ingår i: Solid State Communications. - 0038-1098 .- 1879-2766. ; 113:12, s. 703-708
  • Tidskriftsartikel (refereegranskat)abstract
    • Due to possible technological applications in opto-electronic devices, the interest in characterizing porous silicon structure patterns has recently increased. From scanning force microscopy (SFM) we have obtained images of different samples of porous silicon and applied pattern characterization operators on these matrices. In this paper, asymmetric spatial fragmentation in amplitude envelopes of porous silicon samples are characterized by means of a parameter that quantifies the amount of spatial asymmetry in the gradient field. The results show that this method is well suited to characterize silicon porosity quantitatively.
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10.
  • Inganäs, Olle, et al. (författare)
  • Recent progress in thin film organic photodiodes
  • 2001
  • Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 121:1-3, s. 1525-1528
  • Tidskriftsartikel (refereegranskat)abstract
    • We review current developments in organic photodiodes, with special reference to multilayer thin film optics, and modeling of organic donor-acceptor photodiodes. We indicate possibilities to enhance light absorption in devices by nanopatterning as well as by blending, and also discuss materials science issues of nanostructure in blends and in vertically stratified multilayer devices. Our current best devices have external efficiencies of 30-50% in between 400-600 nm, and show fill factors of 0.54 illuminated under weak monochromatic light.
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