1,720,968 research outputs found
Solution-processable polymer based photovoltaic devices with concentration graded bilayers made via composition control of a poly(3-hexylthiophene)/[6,6]-phenyl C-61-butyric acidmethyl ester
No full textThe bulk-heterojunction (BHJ) active layer, prepared by a spin-coating process, has been extensively investigated for its large donor-acceptor interfacial contact area, which can result in increased photo-current density. It is known that a concentration graded structure would enhance not only the charge generation but also charge transport, but, it is very difficult to exhibit such structure in BHJ system. The reason is that the morphology of the BHJ originates from self organization during the thermal annealing step. In this paper, polymer based photovoltaic (PV) devices with concentration graded bilayers have been successfully fabricated for the first time by solution process with various composition controlled poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C-61-butyric acidmethyl ester (PCBM) mixtures. The concentration profiles have been confirmed by Auger electron spectroscopy. The optimized bilayer devices with uniform morphology show enhanced photocurrent density and power conversion efficiency when compared to those exhibited by BHJ based PV devices.This research was supported by Basic Science Research Program
through the National Research Foundation of Korea (NRF)
funded by the Ministry of Education, Science and Technology
(2009-0083540). The authors (D.H.W and O.O.P) of the Korea
Advanced Institute of Science and Technology acknowledge the
support of World Class University (WCU) program through the
NRF of MEST (R32-2008-000-10142-0). This work (Prof. J. H.
Park) was also partially supported by a grant from the Fundamental
R&D Program for Core Technology of Materials funded
by the Ministry of Knowledge Economy, Republic of Korea
Photovoltaic Devices with an Active Layer from a Stamping Transfer Technique: Single Layer Versus Double Layer
No full textIn this study, organic photovoltaic devices with single or double-layered active film were prepared from a stamping transfer technique. A P3HT/PCBM single-layered active layer and a ratio-controlled P3HT/PCBM double-layered active can be successfully fabricated with the help of ultraviolet curable polycarbonate films via a stamping transfer technique. The maximum conversion efficiency values 2.85 for a single active layer transferred device and 3.24% for an optimized double active layer transferred device. Even though transferred double layers should have a sharp interface boundary, an intermixed zone with a concentration gradient was generated by the interpenetration of a donor-rich layer and an acceptor-rich layer in a thermal annealing process. The generation of the intermixed zone is confirmed by Auger electron spectroscopy. The enhanced conversion efficiency levels are attributed to the increased efficiency of the carrier transporting process, which is due to the fact that the concentration gradient is combined with the efficient charge generation from the bulk heterojunction layers.This work was supported by a grant from
the ERC program of National Research Foundation (NRF)
funded by theKorea Ministry of Education, Science and Technology
(MEST) (No. R11-2007-045-01002-0(2009)). This research
was also partially supported by Basic Science Research Program
through the National Research Foundation of Korea (NRF)
funded by the Ministry of Education, Science and Technology
(2009-0083540). D.G.C. and K.J.L. acknowledge the support
from a grant (M102 KN010001-08K1401-00210) from CNMM
Patterned colloidal photonic domes and balls derived from viscous photocurable suspensions
No full textPixelated patterns of photonic hemispheres are prepared by self-organization of silica particles in photocurable hemispherical droplets. Especially, RGB-color patterns with high coverage are fabricated by spotting 3x without coalescence and multicolored hemispheres are prepared by controlled coalescence. In addition, monodisperse photonic balls are prepared through the evolution of wettability of the suspension droplets
Active layer transfer by stamping technique for polymer solar cells: Synergistic effect of TiOx interlayer
No full textSeveral groups reported fabrication method of organic solar cells through a stamping technique by using PDMS mold. Although PDMS is a good stamp material, they have several problems in polymer transfer printing, especially when we use organic solvent (easily swollen). In this study, the polymer solar cells with an active layer of BHJ are successfully prepared via a simple imprinting transfer technique with help of UV-curable resin-coated polycarbonate (UV-PC) film. The transferred BHJ active layer from UV-PC film was perfectly retained at 220-nm thick on top of the PEDOT:PSS-coated ITO glass, and the device showed enhanced J(sc) and device performance up to 3.19% after insertion of the TiOx interlayer between the active layer and Al cathode. This unique imprinting transfer can be considered as an alternative approach to replace the spin-coating when the matters, pre-coated layers are affected by the solvent for next layer. (C) 2010 Elsevier B. V. All rights reserved.This work was supported by WCU (World Class University)
program through the National Research Foundation of
Korea funded by the Ministry of Education, Science and
Technology (R32-2008-000-10142-0). This research was
also partially supported by Basic Science Research Program
through the National Research Foundation of Korea (NRF)funded by the Ministry of Education, Science and Technology
(2009-0083540). One of the authors of KIMM (Choi)
acknowledges the support from a grant (M102KN010001-
08K1401-00210) from CNMM
Patterned Arrays of Au rings for localized surface plasmon resonance
No full textIn this paper, we examined the characteristic behavior of localized surface plasmon resonances (LSPR) of Au dot and ring arrays in response to the selective binding of biomolecules. To do this, patterned arrays of Au rings and dots with various feature scales were fabricated over large areas by an imprint lithography technique. Our results showed that the LSPR spectra of the Au nanorings exhibited a blue shift with increase in the ring widths and asymptotically converged to those for Au nanodots. This clearly implies that the LSPR spectra can be tuned over an extended wavelength range by varying the ring width. For an illustrative purpose, the patterned Au structures were used to detect the binding of streptavidin to biotin. In doing this, the Au patterns were chemically modified with G4 dendrimers of amine terminated poly(amidoamine), which facilitated the tethering of biotin onto the Au pattern. Exposure of the biotinylated Au nanorings to aqueous streptavidin solution induced both red-shifts of the LSPR spectra and changes in the peak intensities. The sensitivity of the LSPR spectra to the binding of the biomolecules was enhanced as the ring width of Au rings was decreased
Characterization of adhesion property between fused silica and thermoplastic polymer film in thermal nanoimprint lithography using a novel pull-off test
No full textA novel pull-off test that mimics the actual thermal NIL process was conducted to investigate the adhesion properties between a flat fused silica and thermoplastic polymer film used in thermal NIL process. The pull-off force was measured under various NIL conditions such as use of various polymer materials, imprint pressures, and separation velocities-and the surfaces of the mold and polymer film were observed after the test. The anti-sticking layer (ASL) derived from (1H,1H,2H,2H-perfluorooctyl)trichlorosilane (F(13)-OTS) was coated on the fused silica and its effects on the adhesion characteristics was also examined. In cases of the mold without ASL, the pull-off force varied significantly according to the process conditions and damage on the polymer film was observed in most of the tests. In cases of the mold coated with the ASL, on the other hands, the pull-off force was maintained at a lower level in the range of the imprint pressure from 2 to 10 MPa or separation velocity from 1 to 25 mu m/s, and there was no damage to the polymer film due to adhesion. (c) 2010 Elsevier B.V. All rights reserved
Controlled fabrication of hollow metal pillar arrays using colloidal masks
No full textCreative Research Initiative
Program of the Ministry of Science and Technology and BK21 Progra
Effect of the ordered 2D-dot nano-patterned anode for polymer solar cells
No full textA patterned conducting IZO film with well-ordered periodic dot-structures with 50 or 200 nm deep features has been constructed by nanoimprinting technique as the anode of an organic solar cell. The use of the patterned anode leads to an increase in the short circuit current (J(sc)) from 7.03 to 8.94 mA/cm(2) and the power conversion efficiency (PCE) from 1.05 to 1.71% compared to the. at anode. The open circuit voltage (V(oc)) is also affected by nano-patterned structure. The PCE is also influenced by the aspect ratio of the pattern structure. (C) 2009 Elsevier B.V. All rights reserved.This work was supported by the grant from the ERC
program of the Korea Science and Engineering Foundation (KOSEF) funded by the Korea Ministry of Education, Science
and Technology (MEST) (No. R11-2007-045-01002-
0(2009)). Author of SKKU (J.H. Park) acknowledge the support
from the Hydrogen Energy R&D Center, one of the 21st
Century Frontier R&D Program, funded by the Ministry of
Education, Science and Technology of Korea. Authors of
KIMM (Choi and Jeong) acknowledge the support from a
grant (M102KN010001-08K1401-00210) from CNMM
Optical Tunneling Mediated Sub-Skin-Depth High Emissivity Tungsten Radiators
No full textTailoring the spectrum of thermal radiation at high temperatures is a central issue in the study of thermal radiation harnessed energy resources. Although bulk metals with periodic cavities incorporated into their surfaces provide high emissivity, they require a complicated micron metal etch, thereby precluding reliable, continuous operation. Here, we report thermally stable, highly emissive, ultrathin (<20 nm) tungsten (W) radiators that were prepared in a scalable and cost-effective route. Alumina/W/alumina multiwalled, submicron cavity arrays were fabricated sequentially using nanoimprinting lithography, thin film deposition, and calcination processes. To highlight the practical importance of high-temperature radiators, we developed a thermophotovoltaic (TPV) system equipped with fabricated W radiators and low-bandgap GaSb photovoltaic cells. The TPV system produced electric power reliably during repeated temperature cycling between 500 and 1200 K; the power density at 1200 K was fixed to be approximately 1.0 W/cm(2). The temperature-dependent electric power was quantitatively reproduced using a one-dimensional energy conversion model. The symmetric configuration of alumina/W/alumina multiwall together with the presence of a void inside each cavity alleviated thermal stress, which was responsible for the stable TPV performance. The short-current-density (J(sc)) of developed TPV system was augmented significantly by decreasing the W thickness below its skin depth. A 17 nm thick W radiator yielded a 32% enhancement in J(sc) compared to a 123 nm thick W radiator. Electromagnetic analysis indicated that subskin-depth W cavity arrays led to suppressed surface reflection due to the mitigated screening effect of free electrons, thereby enhancing the absorption of light within each W wall. Such optical tunneling-mediated absorption or radiation was valid for any metal material and morphology (e.g., planar or patterned).
Spontaneous Additive Nanopatterning from Solution Route Using Selective Wetting
No full textNanopatterns of functional materials have successfully led innovations in a wide range of fields, but further exploration of their full potential has often been limited because of complex and cost-inefficient patterning processes. We here propose an additive nanopatterning process of functional materials from solution route using selective wetting phenomenon. The proposed process can produce nanopatterns as narrow as 150 nm with high yield over large area at ultrahigh process speed, that is, the speed of solution dragging, of up to ca. 4.6 m.min(-1). The process is highly versatile that it can utilize a wide range of solution materials, control vertical structures including pattern thickness and multistacks, and produce nanopatterns on various substrates with emerging form factors such as foldability and disposability. The solution patterning in nanoscale by selective wetting is enabled by corresponding surface energy patterns in high contrast that are achieved by one-step imprinting onto hydrophobic/hydrophilic bilayers. The mechanisms and control parameters for the solution patterning are revealed by fluid-dynamic simulation. With the aforementioned advantages, we demonstrate 25 400 pixel-per-inch light-emitting pixel arrays and a plasmonic color filter of 10 cm x 10 cm area on a plastic substrate as potential applications.
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