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ABSTRACT: Hybrid phototransistors (HPTRs) were fabricated on glass substrates using organic/inorganic hybrid bulk heterojunction films of p-type poly(3-hexylthiophene) (P3HT) and n-type zinc oxide nanoparticles (ZnO(NP)). The content of ZnO(NP) was varied up to 50 wt % in order to understand the composition effect of ZnO(NP) on the performance of HPTRs. The morphology and nanostructure of the P3HT:ZnO(NP) films was examined by employing high resolution electron microscopes and synchrotron radiation grazing angle X-ray diffraction system. The incident light intensity (P(IN)) was varied up to 43.6 μW/cm(2), whereas three major wavelengths (525 nm, 555 nm, 605 nm) corresponded to the optical absorption of P3HT were applied. Results showed that the present HPTRs showed typical p-type transistor performance even though the n-type ZnO(NP) content increased up to 50 wt %. The highest transistor performance was obtained at 50 wt %, whereas the lowest performance was measured at 23 wt % because of the immature bulk heterojunction morphology. The drain current (I(D)) was proportionally increased with P(IN) due to the photocurrent generation in addition to the field-effect current. The highest apparent and corrected responsivities (R(A) = 4.7 A/W and R(C) = 2.07 A/W) were achieved for the HPTR with the P3HT:ZnO(NP) film (50 wt % ZnO(NP)) at P(IN) = 0.27 μW/cm(2) (555 nm).
ACS Applied Materials & Interfaces 02/2013; 5(4):1385-92. · 4.53 Impact Factor
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ABSTRACT: Simulating protein unfolding under pressure with a coarse-grained model JCP: BioChem. Phys. 6, 11B607 (2012) Simulating protein unfolding under pressure with a coarse-grained model J. Chem. Phys. 137, 185102 (2012) Efficient energy transfer in light-harvesting systems: Quantum-classical comparison, flux network, and robustness analysis JCP: BioChem. Phys. 6, 11B601 (2012) Efficient energy transfer in light-harvesting systems: Quantum-classical comparison, flux network, and robustness analysis J. Chem. Phys. 137, 174111 (2012) Nano-islands integrated evanescence-based lab-on-a-chip on silica-on-silicon and polydimethylsiloxane hybrid platform for detection of recombinant growth hormone Biomicrofluidics 6, 046501 (2012) Additional information on Appl. Phys. Lett.
Applied Physics Letters 11/2012; 101. · 3.84 Impact Factor
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ABSTRACT: We report an enhancement in the efficiency of organic solar cells via the incorporation of gold (Au) or silver (Ag) nanoparticles (NPs) in the hole-transporting buffer layer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), which was formed on an indium tin oxide (ITO) surface by the spin-coating of PEDOT:PSS-Au or Ag NPs composite solution. The composite solution was synthesized by a simple in situ preparation method which involved the reduction of chloroauric acid (HAuCl4) or silver nitrate (AgNO3) with sodium borohydride (NaBH4) solution in the presence of aqueous PEDOT:PSS media. The NPs were well dispersed in the PEDOT:PSS media and showed a characteristic absorption peak due to the surface plasmon resonance effect. Organic solar cells with the structure of ITO/PEDOT:PSS-Au, Ag NPs/poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM)/LiF/Al exhibited an 8% improvement in their power conversion efficiency mainly due to the enlarged surface roughness of the PEDOT:PSS, which lead to an improvement in the charge collection and ultimately improvements in the short-circuit current density and fill factor.
Nanoscale Research Letters 11/2012; 7(1):641. · 2.73 Impact Factor
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ABSTRACT: We report the improved performance of all-polymer solar cells with bulk heterojunction nanolayers of an electron-donating polymer (poly(3-hexylthiophene) (P3HT)) and an electron-accepting polymer (poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT)), which were both doped with 4-ethylbenzenesulfonic acid (EBSA). To choose the doping ratio of P3HT for all-polymer solar cells, various EBSA doping ratios (0, 1, 3, 5, 10, 20 wt%) were tested by employing optical absorption spectroscopy, photoluminescence spectroscopy, photoelectron yield spectroscopy, and space-charge-limited current (SCLC) mobility measurement. The doping reaction of P3HT with EBSA was followed by observing the colour change in solutions. The final doping ratio for P3HT was chosen as 1 wt% from the best hole mobility measured in the thickness direction, while that for F8BT was fixed as 10 wt% (F8BT-EBSA). The polymer:polymer solar cells with bulk heterojunction nanolayers of P3HT-EBSA (EBSA-doped P3HT) and F8BT-EBSA (EBSA-doped F8BT) showed greatly improved short circuit current density (J(SC)) and open circuit voltage (V(OC)), compared to the undoped solar cells. As a result, the power conversion efficiency (PCE) was enhanced by ca. 300% for the 6 : 4 (P3HT-EBSA : F8BT-EBSA) composition and ca. 400% for the 8 : 2 composition. The synchrotron-radiation grazing incidence angle X-ray diffraction (GIXD) measurement revealed that the crystallinity of the doped nanolayers significantly increased by EBSA doping owing to the formation of advanced phase segregation morphology, as supported by the surface morphology change measured by atomic force microscopy. Thus the improved PCE can be attributed to the enhanced charge transport by the formation of permanent charges and better charge percolation paths by EBSA doping.
Physical Chemistry Chemical Physics 10/2012; 14(43):15046-53. · 3.57 Impact Factor
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ABSTRACT: We investigated the dispersion effect of crystalline silicon nanoparticles (SiNP) on the performance and stability of organic solar cells with the bulk heterojunction (BHJ) films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C(61)-butyric acid methyl ester (PC(61)BM). To improve the dispersion of SiNP in the BHJ films, we attached octanoic acid (OA) to the SiNP surface via esterification reaction and characterized it with Raman spectroscopy and high-resolution transmission electron microscopy. The OA-attached SiNP (SiNP-OA) showed improved dispersion in chlorobenzene without change of optical absorption, ionization potential and crystal nanostructure of SiNP. The device performance was significantly deteriorated upon high loading of SiNP (10 wt %), whereas relatively good performance was maintained without large degradation in the case of SiNP-OA. Compared to the control device (P3HT:PC(61)BM), the device performance was improved by adding 2 wt % SiNP-OA, but it was degraded by adding 2 wt % SiNP. In particular, the device stability (lifetime under short time exposure to 1 sun condition) was improved by adding 2 wt % SiNP-OA even though it became significantly decreased by adding 2 wt % SiNP. This result suggests that the dispersion of nanoparticles greatly affects the device performance and stability (lifetime).
ACS Applied Materials & Interfaces 10/2012; 4(10):5300-8. · 4.53 Impact Factor
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ABSTRACT: We investigated the influence of nickel oxide (NiO) nanoparticles that are incorporated into the hole-collecting buffer layer [poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)] on the performance of polymer:fullerene solar cells. To understand the optimum composition of NiO nanoparticles, the composition of NiO nanoparticles was varied from 0 wt% to 23 wt%. Results showed that the optical transmittance was gradually decreased as the NiO content increased. However, the device performance (short circuit current density, fill factor, series resistance, power conversion efficiency) exhibited a two stage trend in a boundary of approximately 9 wt% NiO content. This trend was in good agreement with the trend of sheet resistance in the presence of slight discrepancy owing to the different charge transport geometry.
Journal of Nanoscience and Nanotechnology 07/2012; 12(7):5696-9. · 1.56 Impact Factor
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ABSTRACT: We report the microstructure and properties of polyimide molecular composite films fabricated from a rigid rod-like polyimide
[poly(pyromellitic dianhydride-p-phenylene diamine) (PMDA-PDA PI)] and a flexible coil-like poly(amide-imide) [poly(trimellitic anhydride chloride-4,4′-oxydianiline)
(TMAC-ODA PAI)]. The molecular composite films were prepared by the thermal imidization of precursor molecular composite films
consisting of soluble precursors of PMDA-PDA PI and TMAC-ODA PAI. The microstructure of the polyimide/poly(amide-imide) molecular
composite films was characterized by infrared spectroscopy and X-ray diffraction. The thermal, optical, dielectric, and mechanical
properties of the molecular composite films were examined using a thermogravimetric analyzer, differential scanning calorimeter,
prism coupler, impedance analyzer, and universal testing machine. The results showed that the molecular composite films exhibited
a single glass transition, indicating good compatibility between the two components. However, most of the properties showed
a nonlinear trend with the compositions in the presence of a critical point at PMDA-ODA PI/TMAC-ODA PAI = 40/60 (wt/wt).
Keywordsmolecular composite-polyimide-poly(amide-imide)-microstructure-properties
Macromolecular Research 04/2012; 18(1):14-21. · 1.15 Impact Factor
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ABSTRACT: An artificial nose was developed to mimic aspects of sensory transduction of the peripheral mammalian olfactory system. We directly cultured and differentiated rat olfactory sensory neurons (OSNs) on indium-tin oxide electrodes of planar triode substrates without a coupling agent. Direct voltage (~50 μV) and current (~250 nA) signals were measured simultaneously when OSNs on the planar triode substrates were exposed to odorant mixtures. The response signals were sensitive to the concentration of the odorant mixture, with a typical lifetime, shape, and adaptation profile as seen in responses upon repeated stimulation in vivo. We found that the rising time to the peak current was ~161 ms, while the signal back to baseline was in 1.8 s, which are in agreement with the natural intracellular electrophysiological responses. These results provide the first evidence that mature OSNs grown in a planar triode device are able to detect direct electrophysiological responses to odorants.
The Analyst 03/2012; 137(9):2047-53. · 4.23 Impact Factor
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ABSTRACT: We attempted to dope poly(3-hexylthiophene) (P3HT) with 2-ethylbenzenesulfonic acid (EBSA), which has good solubility in organic solvents, in order to improve the performance of organic field effect transistors (OFET). The EBSA doping ratio was varied up to 1.0 wt % because the semiconducting property of P3HT could be lost by higher level doping. The doping reaction was confirmed by the emerged absorption peak at the wavelength of ~970 nm and the shifted S2p peak (X-ray photoelectron spectroscopy), while the ionization potential and nanostructure of P3HT films was slightly affected by the EBSA doping. Interestingly, the EBSA doping delivered significantly improved hole mobility because of the greatly enhanced drain current of OFETs by the presence of the permanently charged parts in the P3HT chains. The hole mobility after the EBSA doping was increased by the factor of 55-86 times depending on the regioregularity at the expense of low on/off ratio in the case of unoptimized devices, while the optimized devices showed ~10 times increased hole mobility by the 1.0 wt % EBSA doping with the greatly improved on/off ratio even though the source and drain electrodes were made using relatively cheaper silver instead of gold.
ACS Applied Materials & Interfaces 02/2012; 4(3):1281-8. · 4.53 Impact Factor
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ABSTRACT: Here we report the characteristics of protein-polymer nanobiocomposite films and their solid state devices. The protein-polymer nanobiocomposite films (thickness = approximately 125 nm) were prepared by spin-coating the solution of cytochrome c (cyt c) and poly(vinyl alcohol) (PVA) (cyt c:PVA = 3:1 by weight). To understand the characteristics of the cyt c-PVA films (nanolayers), we employed the optical absorption and surface morphology measurement and then fabricated planar diode-type solid state devices. The optical absorption measurement showed that the heme part of cyt c in the cyt c-PVA nanolayer was well kept after the coating process, while the crack-like surface was found from the atomic force microscopy measurement. The planar device showed an ohmic type dark current, but the current gradually increased as the incident light intensity increased. In particular, the (photo) current was strongly dependent upon the voltage, which was assigned to the insulating role of cyt c surrounding groups and PVA. This trend was supported by the slow rise and decay time via photo-switching experiment.
Journal of Nanoscience and Nanotechnology 02/2012; 12(2):1226-9. · 1.56 Impact Factor
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ABSTRACT: We report the influence of UV-ozone irradiation of the hole-collecting buffer layers on the performance and lifetime of polymer:fullerene solar cells. UV-ozone irradiation was targeted at the surface of the poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) layers by varying the irradiation time up to 600 s. The change of the surface characteristics in the PEDOT:PSS after UV-ozone irradiation was measured by employing optical absorption spectroscopy, photoelectron yield spectroscopy, and contact angle measurements, while Raman and X-ray photoelectron spectroscopy techniques were introduced for more microscopic analysis. Results showed that the UV-ozone irradiation changed the chemical structure/composition of the surface of the PEDOT:PSS layers leading to the gradual increase of ionization potential with irradiation time in the presence of up-and-down variations in the contact angle (polarity). This surface property change was attributed to the formation of oxidative components, as evidenced by XPS and Auger electron images, which affected the sheet resistance of the PEDOT:PSS layers. Interestingly, device performance was slightly improved by short irradiation (up to 10 s), whereas it was gradually decreased by further irradiation. The short-duration illumination test showed that the lifetime of solar cells with the UV-ozone irradiated PEDOT:PSS layer was improved due to the protective role of the oxidative components formed upon UV-ozone irradiation against the attack of sulfonic acid groups in the PEDOT:PSS layer to the active layer.
ChemSusChem 11/2011; 4(11):1607-12. · 6.83 Impact Factor
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ABSTRACT: We report the application of two-dimensional (2D) photonic crystal (PC) array substrates for polymer:fullerene solar cells of which the active layer is made with blended films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The 2D PC array substrates were fabricated by employing a nanosphere lithography technique. Two different hole depths (200 and 300 nm) were introduced for the 2D PC arrays to examine the hole depth effect on the light harvesting (trapping). The optical effect by the 2D PC arrays was investigated by the measurement of optical transmittance either in the direction normal to the substrate (direct transmittance) or in all directions (integrated transmittance). The results showed that the integrated transmittance was higher for the 2D PC array substrates than the conventional planar substrate at the wavelengths of ca. 400 nm, even though the direct transmittance of 2D PC array substrates was much lower over the entire visible light range. The short circuit current density (JSC) was higher for the device with the 2D PC array (200 nm hole depth) than the reference device. However, the device with the 2D PC array (300 nm hole depth) showed a slightly lower JSC value at a high light intensity in spite of its light harvesting effect proven at a lower light intensity.
Nanotechnology 10/2011; 22(46):465403. · 3.98 Impact Factor
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ABSTRACT: A new oxadiazole-containing brush polymer, poly(5-phenyl-1,3,4-oxadiazol-2-yl-[1,1′-biphenyl]carboxyloxy-n-nonyl acrylate) (PPOXBPA), was synthesized. The polymer was thermally stable up to 350 °C. Below the degradation temperature, it showed a glass transition, crystal melting transition, and a liquid crystal to isotropic melt transition. Its optical and electrochemical properties were also investigated. This brush polymer was found to always self-assemble into a multibilayer structure, with partial interdigitation between bristles from different layers occurring via the π–π stacking of the oxadiazole mesogen units. Interestingly, when the polymer film was applied in devices with a bottom and top electrode, it showed either volatile or nonvolatile memory behavior, depending on the ordering and orientation of the multibilayer structure (particularly, the π–π stacked oxadiazole mesogen units), which could be controlled via thermal annealing. The switching mechanisms of these electrical memory behaviors were investigated. Collectively, these results demonstrate that this chemically well-defined brush polymer is suitable for use as an active material for the low-cost, mass production of high-performance, programmable volatile and nonvolatile memory devices via control of the morphological structure.
09/2011;
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ABSTRACT: We report the nanomorphology-driven two-stage hole mobility in the blend films of regioregular and regiorandom poly(3-hexylthiophene) (P3HT) polymers of which regioregularity was 92.2% and 33.0%, respectively. The hole mobility of blend films was measured by employing a top-contact type organic field-effect transistor which has an aromatic polyimide gate insulating layer and silver source/drain electrodes. Results showed that the hole mobility of blend films was suddenly reduced as large as two orders of magnitude as the bulk regioregularity of blend films decreased from 89.8% to 86.3%, even though the hole mobility change was far less than one order of magnitude after and before this boundary condition. The discontinuous two-stage hole mobility trend has been attributed to the destruction of P3HT chain ordering/alignment in the blend films at the boundary blend composition, as evidenced from the huge changes in optical absorption coefficient, surface nanomorphology, and in-plane/out-of-plane nanostructures in the blend films.
Nanoscale 09/2011; 3(10):4261-9. · 5.91 Impact Factor
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ABSTRACT: We briefly report the effect of film thickness on the performance of hybrid polymer/polymer solar cells that were made using poly(3-hexylthiophene), poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT), and zinc oxide (ZnO) nanoparticles. The ZnO nanoparticles were introduced to improve the electron transport property of P3HT/F8BT blend films. Results showed that the open circuit voltage (V(OC)) was remarkably decreased by adding only approximately 0.5 wt% ZnO nanoparticles though the optical absorption spectra were not much changed due to the small amount of ZnO nanoparticles in the ternary blend films (approximately 1.9%). In contrast, the fill factor (FF) of devices was improved for the ternary blend devices with the ZnO nanoparticles due to the improved electron transport as evidenced by the reduced series resistance. The short circuit current density of devices was not much changed because of the enhanced charge transport. However, the addition of ZnO nanoparticles decreased the power conversion efficiency of devices owing to the larger influence of V(OC) compared to the FF improvement.
Journal of Nanoscience and Nanotechnology 07/2011; 11(7):5733-6. · 1.56 Impact Factor
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ABSTRACT: Low-cost detectors for sensing photons at a low light intensity are of crucial importance in modern science. Phototransistors can deliver better signals of low-intensity light by electrical amplification, but conventional inorganic phototransistors have a limitation owing to their high temperature processes in vacuum. In this work, we demonstrate organic phototransistors with polymer/polymer bulk heterojunction blend films (mixtures of p-type and n-type semiconducting polymers), which can be fabricated by inexpensive solution processes at room temperature. The key idea here is to effectively exploit hole charges (from p-type polymer) as major signaling carriers by employing p-type transistor geometry, while the n-type polymer helps efficient charge separation from excitons generated by incoming photons. Results showed that the present organic transistors exhibited proper functions as p-type phototransistors with ∼4.3 A W(-1) responsivity at a low light intensity (1 µW cm(-2)), which supports their encouraging potential to replace conventional cooled charge coupled devices (CCD) for low-intensity light detection applications.
Nanoscale 05/2011; 3(5):2275-9. · 5.91 Impact Factor
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ABSTRACT: The imide-functionalized polynorbornene films exhibited excellent optical transparency in the visible range as well as high thermal stability over 200 degrees C. The indium tin oxide (ITO) thin films were coated on the imide-functionalized polynorbornene films at various deposition temperatures by employing radio-frequency (r.f.) planar magnetron sputtering system. The resulting ITO-coated imide-functionalized polynorbornene substrates showed good electrical and optical properties, while the figure of merit examination revealed that the present substrates are comparable to conventional ITO-glass substrates. This was confirmed from the preliminary result of organic light-emitting devices fabricated using the imide-functionalized polynorbornene substrates.
Journal of Nanoscience and Nanotechnology 01/2011; 11(1):550-4. · 1.56 Impact Factor
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ABSTRACT: We report the effect of pressing light-absorbing layers on the performance of polymer solar cells. The light-absorbing active layer was prepared on the transparent conducting oxide coated substrates from solutions that contain a mixture of regioregular poly(3-hexylthiophene) and soluble fullerene molecules. The active layers were pressed using a home-built micro-press system by controlling temperature and pressure, followed by the top electrode deposition. The surface of the active layers pressed was examined using atomic force microscope, while the photovoltaic characteristics of devices were measured under simulated solar light illumination (air mass 1.5 G, 100 mW/cm2). Results showed that the dark current of devices was noticeably increased by pressing the active layer without respect to the pressing temperature. The highest power conversion efficiency was achieved for the device with the active layer pressed under 10 kgf at 70 degrees C. The result was explained in terms of surface morphology and thermophysical effect.
Journal of Nanoscience and Nanotechnology 01/2011; 11(1):318-21. · 1.56 Impact Factor
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ABSTRACT: We report thermally stable diimide nanoclusters that could potentially replace the conventional thick electron transport layer (ETL) in organic light-emitting devices (OLEDs). Bis-[1,10]phenanthrolin-5-yl-bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic diimide (Bphen-BCDI) was synthesized from the corresponding dianhydride and amine moieties, and its purified product exhibited a high glass transition temperature (232 °C) and a wide band gap (3.8 eV). The Bphen-BCDI subnanolayers deposited on substrates were found to form organic nanoclusters, not a conventional layer. The OLED made with a subnanolayer of Bphen-BCDI nanoclusters, instead of a conventional ETL, showed greatly improved efficiency (about 2-fold) compared with an OLED without the diimide nanoclusters. The role of the BPhen-BCDI nanoclusters was assigned to hole trapping and electron injection in the present OLED structure.
Nanoscale 12/2010; 3(3):1073-7. · 5.91 Impact Factor
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ABSTRACT: Here we report the effect of gate voltage on the performance of organic phototransistors made using bulk heterojunction films of regioregular poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM). To understand the illumination effect, a monochromatic light (520 nm) corresponded to the maximum absorption of present P3HT:PCBM blend film was employed. Results showed that the present device followed a p-type field-effect transistor in the dark and under illumination though the saturation trend of output curves became weakened under illumination. The responsivity exhibited a two-stage trend as a function of gate voltage. The maximum responsivity reached 0.13 A/W under illumination of green light at 81μW/cm2.
Molecular Crystals and Liquid Crystals. 12/2010; 519(1):260-265.
