A facile and rapid process to fabricate platinum counter electrode in dye-sensitized solar cell using nanosecond pulsed laser sintering at room temperature

To fabricate the platinum (Pt) counter electrode in dye-sensitized solar cells (DSSCs), rapid and low sintering process was carried out using nanosecond pulsed laser sintering (LS) method based on third harmonic (355 nm) of an Nd:YAG laser at room temperature. The surface morphology of LS-Pt on fluorine-doped tin oxide (FTO) electrode showed thin and compact structure, consisting of particles size of - 10-30 nm and thickness of below 30 nm. The DSSCs with the LS-Pt/FTO counter electrodes displayed the power conversion efficiency of 4.4% with short-circuit current = 9.07 mA/cm2, open-circuit voltage = 0.79 V and fill factor = 61.3.

Nanoscopic management of molecular packing and orientation of small molecules by a combination of linear and branched alkyl side chains

We synthesized a series of acceptor-donor-acceptor-type small molecules (SIDPP-EE, SIDPP-EO, SIDPP-OE, and SIDPP-OO) consisting of a dithienosilole (SI) electron-donating moiety and two diketopyrrolopyrrole (DPP) electron-withdrawing moieties each bearing linear n-octyl (O) and/or branched 2-ethylhexyl (E) alkyl side chains. X-ray diffraction patterns revealed that SIDPP-EE and SIDPP-EO films were highly crystalline with pronounced edge-on orientation, whereas SIDPP-OE and SIDPP-OO films were less crystalline with a radial distribution of molecular orientations. Near-edge X-ray absorption fine structure spectroscopy disclosed an edge-on orientation with a molecular backbone tilt angle of ∼22° for both SIDPP-EE and SIDPP-EO. Our analysis of the molecular packing and orientation indicated that the shorter 2-ethylhexyl groups on the SI core promote tight π-π stacking of the molecular backbone, whereas n-octyl groups on the SI core hinder close π-π stacking to some degree. Conversely, the longer linear n-octyl groups on the DPP arms facilitate close intermolecular packing via octyl-octyl interdigitation. Quantum mechanics/molecular mechanics molecular dynamics simulations determined the optimal three-dimensional positions of the flexible alkyl side chains of the SI and DPP units, which elucidates the structural cause of the molecular packing and orientation explicitly. The alkyl-chain-dependent molecular stacking significantly affected the electrical properties of the molecular films. The edge-on oriented molecules showed high hole mobilities in organic field-effect transistors, while the radially oriented molecules exhibited high photovoltaic properties in organic photovoltaic cells. These results demonstrate that appropriate positioning of alkyl side chains can modulate crystallinity and molecular orientation in SIDPP films, which ultimately have a profound impact on carrier transport and photovoltaic performance.

High crystalline dithienosilole-cored small molecule semiconductor for ambipolar transistor and nonvolatile memory

We characterized the electrical properties of a field-effect transistor (FET) and a nonvolatile memory device based on a solution-processable low bandgap small molecule, Si1TDPP-EE-C6. The small molecule consisted of electron-rich thiophene-dithienosilole-thiophene (Si1T) units and electron-deficient diketopyrrolopyrrole (DPP) units. The as-spun Si1TDPP-EE-C6 FET device exhibited ambipolar transport properties with a hole mobility of 7.3×10(-5) cm2/(Vs) and an electron mobility of 1.6×10(-5) cm2/(Vs). Thermal annealing at 110 °C led to a significant increase in carrier mobility, with hole and electron mobilities of 3.7×10(-3) and 5.1×10(-4) cm2/(Vs), respectively. This improvement is strongly correlated with the increased film crystallinity and reduced π-π intermolecular stacking distance upon thermal annealing, revealed by grazing incidence X-ray diffraction (GIXD) and atomic force microscopy (AFM) measurements. In addition, nonvolatile memory devices based on Si1TDPP-EE-C6 were successfully fabricated by incorporating Au nanoparticles (AuNPs) as charge trapping sites at the interface between the silicon oxide (SiO2) and cross-linked poly(4-vinylphenol) (cPVP) dielectrics. The device exhibited reliable nonvolatile memory characteristics, including a wide memory window of 98 V, a high on/off-current ratio of 1×10(3), and good electrical reliability. Overall, we demonstrate that donor-acceptor-type small molecules are a potentially important class of materials for ambipolar FETs and nonvolatile memory applications.

Highly efficient copper-zinc-tin-selenide (CZTSe) solar cells by electrodeposition

Highly efficient copper-zinc-tin-selenide (Cu2ZnSnSe4 ; CZTSe) thin-film solar cells are prepared via the electrodepostion technique. A metallic alloy precursor (CZT) film with a Cu-poor, Zn-rich composition is directly deposited from a single aqueous bath under a constant current, and the precursor film is converted to CZTSe by annealing under a Se atmosphere at temperatures ranging from 400 °C to 600 °C. The crystallization of CZTSe starts at 400 °C and is completed at 500 °C, while crystal growth continues at higher temperatures. Owing to compromises between enhanced crystallinity and poor physical properties, CZTSe thin films annealed at 550 °C exhibit the best and most-stable device performances, reaching up to 8.0 % active efficiency; among the highest efficiencies for CZTSe thin-film solar cells prepared by electrodeposition. Further analysis of the electronic properties and a comparison with another state-of-the-art device prepared from a hydrazine-based solution, suggests that the conversion efficiency can be further improved by optimizing parameters such as film thickness, antireflection coating, MoSe2 formation, and p-n junction properties.

Ahnak functions as a tumor suppressor via modulation of TGFβ/Smad signaling pathway

We provide detailed mechanisms of Ahnak-mediated potentiation of transforming growth factor β (TGFβ) signaling, which leads to a negative regulation of cell growth. We show that Smad3 interacts with Ahnak through MH2 domain and that Ahnak stimulates Smad3 localization into nucleus leading to potentiating TGFβ-induced transcriptional activity of R-Smad. Moreover, overexpression of Ahnak resulted in growth retardation and cell cycle arrest through downregulation of c-Myc and cyclin D1/D2. We describe results from analyses of Ahnak^−/− mouse model expressing middle T antigen in a mammary gland-specific manner (MMTV^Tg/+Ahnak^−/−), which showed significantly progressed hyperplasia of mammary glands compared with MMTV^Tg/+Ahnak^+/+. Finally, we screened multiple human breast cancer tissues and showed that the expression of Ahnak in cancer tissues is lower than that in control tissues by 50%. Taken together, these data indicate that Ahnak mediates a negative regulation of cell growth and acts as novel tumor suppressor through potentiation of TGFβ signaling.

Carrier lifetime extension via the incorporation of robust hole/electron blocking layers in bulk heterojunction polymer solar cells

We report the achievement of a power conversion efficiency (PCE) improvement in P3HT:PCBM-based bulk-heterojunction type polymer solar cells using photocrosslinked P3HT (c-P3HT) as the electron blocking/hole extraction layer and titanium oxide nanoparticles (TiO2) as the hole blocking/electron extraction layer. Devices prepared with a 20 nm thick c-P3HT layer showed an improved PCE of 3.4% compared to devices prepared without the c-P3HT layer (PCE = 3.0%). This improvement was attributed to an extension in the carrier lifetime and an enhancement in the carrier mobility. The incorporation of the c-P3HT layer lengthened (by more than a factor of 2) the carrier lifetime and increased (by a factor of 5) the hole mobility. These results suggest that the c-P3HT layer not only prevented non-geminate recombination but it also improved carrier transport. The PCE was further improved to 4.0% through the insertion of a TiO2 layer that acted as an effective hole-blocking layer at the interface between the photoactive layer and the cathode. This work demonstrates that the incorporation of solution-processable hole and electron blocking/extraction layers offers an effective means for preventing nongeminate recombination at the interfaces between a photoactive layer and an electrode in bulk-heterojunction-type polymer solar cells.

Colloidal solution-processed CuInSe2 solar cells with significantly improved efficiency up to 9% by morphological improvement

We demonstrate here that an improvement in the green density leads to a great enhancement in the photovoltaic performance of CuInSe2 (CISe) solar cells fabricated with Cu-In nanoparticle precursor films via colloidal solution deposition. Cold-isostatic pressing (CIP) increases the precursor film density by ca. 20%, which results in an appreciable improvement in the microstructural features of the sintered CISe film in terms of a lower porosity, a more uniform surface morphology, and a thinner MoSe2 layer. The low-band-gap (1.0 eV) CISe solar cells with the CIP-treated films exhibit greatly enhanced open-circuit voltage (V(OC), typically from 0.265 to 0.413 V) and fill factor (FF, typically from 0.34 to 0.55), compared to the control devices. As a consequence, an almost 3-fold increase in the average efficiency, from 3.0 to 8.2% (with the highest value of 9.02%), is realized. Diode analysis reveals that the enhanced V(OC) and FF are essentially attributed to the reduced reverse saturation current density and diode ideality factor. This is associated with suppressed recombination, likely due to the reduction in recombination sites at grain/air surfaces, intergranular interfaces, and defective CISe/CdS junctions. From the temperature dependences of V(OC), it is revealed that CIP-treated devices suffer less from interface recombination.

Elastic resistance change and action potential generation of non-faradaic Pt/TiO2/Pt capacitors

Electric current in the mixed ionic-electronic conductor TiO2 is hysteretic, i.e. history-dependent, and its use is versatile in electronic devices. Nowadays, biologically inspired, analogue-type computing systems, known as neuromorphic systems, are being actively investigated owing to their new and intriguing physical concepts. The realization of artificial synapses is important for constructing neuromorphic systems. In mammalians' brains, the plasticity of synapses between neighbouring nerve cells arises from action potential firing. Emulating action potential firing via inorganic systems has therefore become important in neuromorphic engineering. In this work, the current-voltage hysteresis of TiO2-based non-faradaic capacitors is investigated to primarily focus on the correlation between the blocking contact and the elasticity, i.e. non-plasticity, of the capacitors' resistance change, in experimental and theoretical methods. The similarity between the action potential firing behaviour in nerve cells and the elasticity of the non-faradaic capacitors is addressed.

Cadmium uptake, chemical forms, subcellular distribution, and accumulation in Echinodorus osiris Rataj

Phytoremediation is a technology for extracting or inactivating pollutants in soil. Echinodorus osiris (E. osiris) is a fast growing perennial wetland plant that is common in tropical and subtropical areas and has a high tolerance to cadmium (Cd). However, the absorption dynamics, subcellular distribution and accumulation of Cd by E. osiris had not been investigated. In this paper, hydroponic experiments with different levels of Cd(2+) (0, 5.0, 15.0 mg L(-1)) were carried out to determine these characteristics of E. osiris. The results indicated that the Cd absorption rate of Echinodorus osiris decreased over time, and the absorption rate within 0.5-1.0 h was faster than after 1.0 h. In a 6.0 hour time period, the rate of Cd uptake fit a quadratic polynomial curve when E. osiris was grown under the 5 mg L(-1) Cd treatment. However, the rate of Cd uptake by E. osiris fit a cubic polynomial model with the 15 mg L(-1) Cd treatment. In the roots, the ethanol-extractable Cd, water-extractable Cd, and NaCl-extractable Cd were the largest proportions of the total Cd. The HAc-extractable Cd, HCl-extractable Cd, and residual-Cd represented a larger proportion of the total Cd in the leaves which was combined with phosphate including CdHPO4, Cd3 (PO4)2, and oxalic acid. When analyzing the subcellular distribution of Cd in the plant, the soluble fraction containing Cd accounted for the largest part (69.49-88.39%) followed by the Cd bound to the cell wall (8.44-25.62%). Both the lower and the higher Cd treatments demonstrated that compartmentation by the vacuole and cell wall binding were two effective defense mechanisms of the plant. However, the vacuole became the main site for Cd accumulation in the leaves under the 15 mg L(-1) Cd treatment. E. osiris was able to accumulate high concentrations of Cd in both the roots and the leaves. The Cd concentration reached 502.97 mg kg(-1) and 2742.95 mg kg(-1) in the shoots and roots, respectively, after 27 days of cultivation. It was concluded that E. osiris is a potential hyperaccumulator of Cd.

Rapid dye adsorption via surface modification of TiO2 photoanodes for dye-sensitized solar cells

A facile method for increasing the reaction rate of dye adsorption, which is the most time-consuming step in the production of dye-sensitized solar cells (DSSCs), was developed. Treatment of a TiO2 photoanode with aqueous nitric acid solution (pH 1) remarkably reduced the reaction time required to anchor a carboxylate anion of the dye onto the TiO2 nanoparticle surface. After optimization of the reaction conditions, the dye adsorption process became 18 times faster than that of the conventional adsorption method. We studied the influence of the nitric acid treatment on the properties of TiO2 nanostructures, binding modes of the dye, and adsorption kinetics, and found that the reaction rate improved via the synergistic effects of the following: (1) electrostatic attraction between the positively charged TiO2 surface and ruthenium anion increases the collision frequency between the adsorbent and the anchoring group of the dye; (2) the weak anchoring affinity of NO3(-) in nitric acid with metal oxides enables the rapid coordination of an anionic dye with the metal oxide; and (3) sufficient acidity of the nitric acid solution effectively increases the positive charge density on the TiO2 surface without degrading or transforming the TiO2 nanostructure. These results demonstrate the developed method is effective for reducing the overall fabrication time without sacrificing the performance and long-term stability of DSSCs.

Photovoltaic properties of high efficiency plastic dye-sensitized solar cells employing interparticle binding agent "nanoglue"

An interparticle binding agent, or nanoglue, was synthesized by a sol-gel process, which facilitated the preparation of well-interconnected TiO2 electrodes at low-temperatures for plastic dye-sensitized solar cells. The viscosity of the nanoglue-based pastes was seven times higher than that obtained in pastes without any nanoglue. The increased viscosity was sufficiently high enough for coating thick films to fabricate TiO2 electrodes. The structural and photovoltaic properties of the films were extensively investigated by varying the amounts of nanoglue. A reduced pore size and greatly enhanced surface area were observed in the nanoglue-based films. Improved interparticle connectivity, resulting in faster electron transport, was confirmed by photocurrent transient spectroscopy and electrochemical impedance measurements of the nanoglue-based films. The electron diffusion length and charge collection efficiency were also enhanced in these nanoglue-based films. A maximum conversion efficiency of 5.43% was achieved in films containing 20 wt% nanoglue fabricated on a plastic substrate under one-sun illumination, even without any additional treatment.

Water-based thixotropic polymer gel electrolyte for dye-sensitized solar cells

For the practical application of dye-sensitized solar cells (DSSCs), it is important to replace the conventional organic solvents based electrolyte with environmentally friendly and stable ones, due to the toxicity and leakage problems. Here we report a noble water-based thixotropic polymer gel electrolyte containing xanthan gum, which satisfies both the environmentally friendliness and stability against leakage and water intrusion. For application in DSSCs, it was possible to infiltrate the prepared electrolyte into the mesoporous TiO2 electrode at the fluidic state, resulting in sufficient penetration. As a result, this electrolyte exhibited similar conversion efficiency (4.78% at 100 mW cm(-2)) and an enhanced long-term stability compared to a water-based liquid electrolyte. The effects of water on the photovoltaic properties were examined elaborately from the cyclic voltammetry curves and impedance spectra. Despite the positive shift in the conduction band potential of the TiO2 electrode, the open-circuit voltage was enhanced by addition of water in the electrolyte due to the greater positive shift in the I(-)/I3(-) redox potential. However, due to the dye desorption and decreased diffusion coefficient caused by the water content, the short-circuit photocurrent density was reduced. These results will provide great insight into the development of efficient and stable water-based electrolytes.

Porcine feasibility and safety study of a new paclitaxel-eluting biliary stent with a Pluronic-containing membrane

BACKGROUND AND STUDY AIM

Metal stents for malignant biliary obstruction are susceptible to occlusion by tumor ingrowth or overgrowth. Therefore, we previously reported our use of a metal stent covered with a paclitaxel-incorporated membrane giving an antitumor effect to prevent occlusion from tumor ingrowth. We have also developed a new generation of paclitaxel-eluting biliary stent using a membrane containing Pluronic F-127 for effective drug delivery. The aim of this study was to investigate the safety and efficacy of drug delivery for this newly developed stent in the biliary tract.

METHODS

Metal stents were coated with paclitaxel and various concentrations of Pluronic F-127 in phosphate-buffered saline solution. Stents containing varying concentrations were placed in the bile ducts of eight pigs divided as follows: group I, 0% Pluronic + 0% paclitaxel; group II, 0% Pluronic + 10% paclitaxel; group III, 10% Pluronic + 10% paclitaxel; group IV, 20% Pluronic + 10% paclitaxel. The histology of the porcine bile duct and the amount of paclitaxel in the porcine serum were examined. The amount of paclitaxel released was also measured in vitro.

RESULTS

Histologic changes in the porcine biliary epithelium were acceptable in terms of safety, based on inflammatory cell infiltration and fibrotic reaction. No significant differences in histology were observed between the groups. In the porcine serum analysis, released paclitaxel was detected for 28 days with the 10% Pluronic concentration (group III). However, released paclitaxel was observed for only 7 days in groups II and IV. In the in vitro experiments, long-lasting release of paclitaxel was also noted from the stent with 10% Pluronic.

CONCLUSIONS

The new paclitaxel-eluting stent with 10% Pluronic F-127 is safe and provides enhanced local drug delivery.

Suppressed recombination in quantum dot-sensitized solar cells with blocking layers on FTO substrates

The compact and thin TiO2 blocking layers (c-TiO2) were formed on F-doped SnO2 (FTO) substrate in quantum dots-sensitized solar cells (QSSCs) by chemical deposition. The c-TiO2 layers induced indirect contact between electrolyte and FTO electrode, which reduced leakage in QSSCs. The QSSCs showed power conversion efficiency (Eff) of 3.85% in the presence of c-TiO2 layers which leads to 21% improved compared to that without c-TiO2 layers (Eff = 3.18%). The presence of the c-TiO2 layers in QSSCs also improved the stability under illumination.

Expanding the spectral response of a dye-sensitized solar cell by applying a selective positioning method

We have developed a facile method to position different dyes (N719 and N749) sequentially in a mesoporous TiO(2) layer through selective desorption and adsorption processes. From the selective removal of the only upper part of the first adsorbed dye, double-layered dye-sensitized solar cells have been successfully achieved without any damage to the dye. From the incident photon-to-current conversion efficiency (IPCE) measurement, the multi-layered dye-sensitized solar cell (MDSSC) was found to exhibit an expanded spectral response for the solar spectrum while maintaining the maximum IPCE value of each single-layered cell. The highest photocurrent density, 19.3 mA cm( - 2), was obtained from the MDSSC utilizing an N719/N749 bi-layered mesoporous TiO(2) film. The power conversion efficiency of 9.8% was achieved from the MDSSC, which is higher than that of single N719-or N749-based cells and cocktail-dyed (a mixture of N719 and N749) cells.

An EMF cell with a nitrogen solid electrolyte--on the transference of nitrogen ions in yttria-stabilized zirconia

The mobility and electrochemical activity of nitrogen inside and/or at the surface of ionic compounds is of fundamental, as well as of possibly practical, relevance. In order to better understand the role of nitrogen anions in solid electrolytes, we measured the transference number of nitrogen in yttria-stabilized zirconia (YSZ) by a concentration cell technique as a function of oxygen activity at different temperatures in the range of 1023 ≤T/K≤ 1123. YSZ doped with 1.9 wt% of N (YSZ:N) turned out to have an appreciable nitrogen transference number, which increased from 0 to 0.1 with decreasing oxygen activity in the range of -20 < log a(O(2)) < -14. The stability of N in YSZ:N, however, has yet to be elucidated under oxidizing conditions.