Faruk Özel

Penternary chalcogenides nanocrystals as catalytic materials for efficient counter electrodes in dye-synthesized solar cells

The penternary chalcogenides Cu2CoSn(SeS)4 and Cu2ZnSn(SeS)4 were successfully synthesized by hot-injection method, and employed as a catalytic materials for efficient counter electrodes in dye-synthesized solar cells (DSSCs). The structural, compositional, morphological and optical properties of these pentenary semiconductors were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), energy-dispersive spectrometer (EDS) and ultraviolet-visible (UV–Vis) spectroscopy. The Cu2CoSn(SeS)4 and Cu2ZnSn(SeS)4 nanocrystals had a single crystalline, kesterite phase, adequate stoichiometric ratio, 18–25 nm particle sizes which are forming nanospheres, and band gap energy of 1.18 and 1.45 eV, respectively. Furthermore, the electrochemical impedance spectroscopy and cyclic voltammograms indicated that Cu2CoSn(SeS)4 nanocrystals as counter electrodes exhibited better electrocatalytic activity for the reduction of iodine/iodide electrolyte than that of Cu2ZnSn(SeS)4 nanocrystals and conventional platinum (Pt). The photovoltaic results demonstrated that DSSC with a Cu2CoSn(SeS)4 nanocrystals-based counter electrode achieved the best efficiency of 6.47%, which is higher than the same photoanode employing a Cu2ZnSn(SeS)4 nanocrystals (3.18%) and Pt (5.41%) counter electrodes. These promising results highlight the potential application of penternary chalcogen Cu2CoSn(SeS)4 nanocrystals in low-cost, high-efficiency, Pt-free DSSCs.

Humidity adsorption kinetics of calix[4]arene derivatives measured using QCM technique

This study focuses on the characterization of sulphonated calix[4]arene derivative films coated on a quartz substrate with a thickness of 40 nm by spin coating method for humidity detection. The humidity adsorption kinetics of the sulphonated calix[4]arene films was investigated by quartz crystal microbalance (QCM) technique. The Langmuir model was used to determine the adsorption rates and Gibbs free energy for various relative humidities between 11% and 97%. Our reproducible experimental results show that suphonated calix[4]arene films have a great potential for humidity sensing applications at room temperature operations.

Mechanical properties of zirconia after different surface treatments and repeated firings.

PURPOSE This study investigated the influence of surface conditioning procedures and repeated firings on monoclinic content and strength of zirconia before cementation. MATERIALS AND METHODS Sintered bar-shaped zirconia specimens were subjected to no surface treatment (control), air abrasion, or grinding (n=21). Their roughness was evaluated using a profilometer, and microscope analysis was performed on one specimen of each group. Then, 2 or 10 repeated firings (n=10) were executed, the monoclinic content of specimens was analyzed by X-ray diffraction, and a three-point flexural strength test was performed. Surface roughness values were compared using one-way analysis of variance (ANOVA) and Tukey honestly significant difference (HSD) tests, the monoclinic content values were tested using Kruskal-Wallis and Mann-Whitney U tests, and the flexural strength values were tested using two-way ANOVA and Tukey HSD tests (P=.05). Spearmans correlation test was performed to define relationships among measured parameters. RESULTS Surface-treated specimens were rougher than untreated specimens and had a higher monoclinic content (P<.005), and the relationship between roughness and monoclinic content was significant (P<.000). Neither surface treatment nor firing significantly affected the flexural strength, but Weibull analysis showed that for the air-abraded samples the characteristic strength was significantly lower after the 10th firing than after the 2nd firing. CONCLUSION After firing, a negligible amount of monoclinic content remained on the zirconia surfaces, and rougher surfaces had higher monoclinic contents than untreated surfaces. Multiple firings could be performed if necessary, but the fracture probability could increase after multiple firings for rougher surfaces.

Luminescence Enhancement of Oled Performance by Doping Colloidal Magnetic FE 3 O 4 Nanoparticles

We report synthesis of magnetic Fe3O4 nanoparticles (MNPs) based on two phase method and their application in organic light-emitting devices (OLEDs) as blend with emissive Poly∞uorene (PFO) matrix. Two phase method allows to successively synthesizing oleic acid capped MPNs with 5{10nm particle size. Colloidal MNPs can be easily mixed with emissive polymer solutions to obtain a blend for OLED application. The electroluminescence e-ciency increases by doping with MNPs into emissive layer. Difierent dopant concentrations varied from 0,4% to 2% were monitored. It was observed that the electroluminescence increases up to 1%w/v doping ratio. The luminance of OLEDs increased from 15.000cd/m 2 to 24.000cd/m 2 in comparison pristine device with 1% MNP doped device.

Photocatalytic Hydrogen Evolution by Oleic Acid‐Capped CdS, CdSe, and CdS0.75Se0.25 Alloy Nanocrystals

Photocatalytic generation of hydrogen by using oleic acid-capped CdS, CdSe, and CdS(0.75)Se(0.25) alloy nanocrystals (quantum dots) has been investigated under visible-light irradiation by employing Na(2)S and Na(2)SO(3) as hole scavengers. Highly photostable CdS(0.75)Se(0.25) alloy nanocrystals gave the highest hydrogen evolution rate (1466 μmol h(-1) g(-1)), which was about three times higher than that of CdS and seven times higher than that of CdSe.

Improvement in electrical performance of half-metallic Fe3O4/GaAs structures using pyrolyzed polymer film as buffer layer

In this work, the Fe3O4 magnetic nanoparticles (MNPs) were synthesized by a colloidal method. TEM images reveal that Fe3O4 MNPs are spherical in shape with a narrow size distribution in the range of 6–7 nm. These MNPs were used in the fabrication of two types of n-GaAs-based structures: (i) Fe3O4/n-GaAs (reference); and (ii) Fe3O4/PPF/n-GaAs. We present that carbon-based pyrolyzed polymer films (PPFs), as a buffer layer, can control the electrical characteristics of a conventional Fe3O4/n-GaAs device. The behaviour of the apparent barrier height and ideality factor with the interfacial layer due to the presence of the interface state density is discussed. PPF raises the barrier height in a Fe3O4/PPF/n-GaAs half-metallic/insulator/semiconductor (h-MIS) device as high as 0.62 0.002 eV. Furthermore, Fe3O4/PPF interfaces exhibit unique electronic properties including high-quality interface, low series resistance (from 17.73 kΩ to 85.66 Ω) and extremely low interface state density (1.76 × 1012 eV−1 cm−2). Compared to the electrical performance for the Fe3O4/n-GaAs junction, that for the Fe3O4/PPF/n-GaAs junction was enhanced.