Yusuf Selim Ocak

Barrier height enhancement of metal/ semiconductor contact by an enzyme biofilm interlayer

A metal/interlayer/semiconductor (Al/enzyme/p-Si) MIS device was fabricated using α-amylase enzyme as a thin biofilm interlayer. It was observed that the device showed an excellent rectifying behavior and the barrier height value of 0.78 eV for Al/α-amylase/p-Si was meaningfully larger than the one of 0.58 eV for conventional Al/p-Si metal/semiconductor (MS) contact. Enhancement of the interfacial potential barrier of Al/p-Si MS diode was realized using enzyme interlayer by influencing the space charge region of Si semiconductor. The electrical properties of the structure were executed by the help of current–voltage and capacitance–voltage measurements. The photovoltaic properties of the structure were executed under a solar simulator with AM1.5 global filter between 40 and 100 mW/cm2 illumination conditions. It was also reported that the α-amylase enzyme produced from Bacillus licheniformis had a 3.65 eV band gap value obtained from optical method.

The novel pyridine based symmetrical Schiff base ligand and its transition metal complexes: synthesis, spectral definitions and application in dye sensitized solar cells (DSSCs)

The pyridine based azo-linked symmetrical Schiff base ligand, (E)-2,2′-((1E,1′E)-(pyridine-2,6-diylbis(azanylylidene))bis(methanylylidene))bis(4-((E)-phenyldiazenyl)phenol) (H2L), and its Co(II), Ni(II) and Pd(II) transition metal complexes were prepared, and defined by using elemental analysis, Fourier transform infrared, UV–visible, mass, nuclear magnetic resonance spectra, molar conductance, magnetic susceptibility and thermal analysis techniques. The conductivity results pointed out the non-electrolytic nature of all metal complexes. Elemental composition, ultraviolet spectra and magnetic susceptibility data showed that the synthesized complexes are in the binuclear structure and square plane geometry. When compared to the characteristic infrared bands for the functional groups of the ligand structure with complex molecules are reached, the ligand binds to the metal atom via phenolic OH and azomethine-nitrogen. Furthermore, the dye-sensitized solar cells (DSSCs) based on H2L and its metal complexes were fabricated, and photovoltaic properties of these devices were also investigated. The power conversion efficiency of fabricated devices based on ligand H2L can be improved with the incorporation of the transition metal complex.

Diester Molecules for Organic-Based Electrical and Photoelectrical Devices

Diester derivatives of terephthalic acid molecules were synthesized according to the literature. Au/Diester derivatives/n-Si organic–inorganic (OI) heterojunction-type devices were fabricated, and the current–voltage (I–V) characteristics of the devices have been investigated at room temperature. I–V characteristics demonstrated that all diodes had excellent rectification properties. Primary diode parameters such as series resistance and barrier height were extracted by using semi-log I–V plots and Norde methods, and were compared. It was seen that there was a substantial agreement between results obtained from two methods. Calculated barrier height values were about the same with 0.02-eV differences that were attributed to the series resistance. Ideality factors, which show how the diode closes to ideal diodes, were also extracted from semi-log I–V plots. Thus, the modification of the Au/n-Si diode potential barrier was accomplished using diester derivatives as an interlayer. The I–V measurements were repeated to characterize the devices at 100 mW/cm2 illumination intensity with the help of a solar simulator with an AM1.5G filter.

Synthesis, characterization, and Schottky diode applications of low-cost new chitin derivatives

In this study, low-cost two new chitin derivatives were first synthesized. Products formed in the consequence of the reaction of chitin with 4-nitrobenzoyl chloride and 3,5-dinitrobenzoyl chloride were named C4NC and C35DC, respectively. Then, C4NC and C35DC were characterized by FTIR and 13C CP-MAS solid-state NMR spectroscopies and X-ray powder diffraction technique. Surface topography and composition of C4NC and C35DC with a scanning electron microscope were investigated. Mass loss in C4NC and C35DC with thermogravimetric analysis method was determined as a function of increasing temperature. Endothermic and exothermic transitions in C4NC and C35DC were investigated with differential thermal analysis and differential scanning calorimetry techniques. Later on, charge carrier density, hole mobility, and electrical conductivity values of C4NC and C35DC were determined. Besides, Schottky diodes of C4NC and C35DC were constructed, and several parameters related to these diodes were determined. Finally, the sensitivity of these diodes to light was studied.

Substrate temperature effects on reactively sputtered Cr2O3/n-Si heterojunctions

To see the effects of substrate temperature on Cr2O3/n-Si heterojunctions, Cr2O3 thin films were formed on n-Si and glass substrates at 40, 150 and 250 °C by radio frequency (RF) reactive sputtering technique. High purity Cr was used as target and oxygen was used as reactive gas. Optical properties of Cr2O3/n-Si thin films were analyzed using UV-vis data. The band gaps of the films were compared. The electrical properties of Cr2O3/n-Si heterojunction were tested by their current voltage (I-V) measurements in dark. It was observed that the heterojunction which was fabricated by forming Cr2O3 thin film at 250 °C gave better rectification. The characteristic electrical parameters such as barrier height, ideality factor and series resistance were calculated by using its I-V data. The influence of light intensity on photovoltaic effect behavior of the device was also calculated, finally the barrier height value of the structure obtained from capacitance-voltage (C-V) data were compared with the one calculated from I-V measurements.

The sprayed ZnO films: nanostructures and physical parameters

We synthesized the pure and indium-doped (IZO) ZnO films with a facile composition control spray pyrolysis route. The substrate temperature (Ts) and In-doping effects on the properties of as-grown films are investigated. The X-ray pattern confirms that the as-synthesized ZnO phase is grown along a (002) preferential plane. It is revealed that the crystalline structure is improved with a substrate temperature of 350 °C. Moreover, the morphology of as-grown films, analyzed by AFM, shows nanostructures that have grown along the c-axis. The (3 × 3 μm2) area scanned AFM surface studies give the smooth film surface RMS < 40 nm. The UV–VIS–IR measurements reveal that the sprayed films are highly transparent in the visible and IR bands. The photoluminescence analysis shows that the strong blue and yellow luminescences of 2.11 and 2.81 eV are emitted from ZnO and IZO films with a slight shift in photon energy caused by In-doping. The band gap is a bit widened by In-doping, 3.21 eV (ZnO) and 3.31 eV (IZO) and the resistivity is reduced from 385 to 8 Ωm. An interesting result is the resistivity linear dependence on the substrate temperature of pure ZnO films.

Analysing Enhancement of Electricity Generating Capacity with Solar Tracking System of the Most Sunning Region of Turkey

Despite the increasingly widespread production of electricity from solar energy and despite Turkey is in the sun belt, Turkey cannot used its potential sufficiently effective and widely. Especially, this situation is of more importance for the Southeastern Anatolia Region Turkeys most sunning area. In this study, among renewable energy resources the generation of electricity from solar energy in terms of both its current potential and production technologies and the solar energy potential of Southeastern Anatolia Region provinces and the degree and method of using this potential to generate electricity have been investigated. Suggestions have been made to benefit from the solar energy in a way of effective and widespread for Southeastern Anatolia Region. Also, a suggestion for convenient place which is 130 m 2 and was formed by Karacadag volcanic eruption and is not used for agriculture and rocky area has been made.

Synthesis and properties of Au/PVP/p-Si/Al heterojunction diode

Properties of heterojunction diodes having polyvinyl pyrrolidone (PVP) on p-Si substrate are investigated. PVP layer has grown onto p type silicon substrate via the sol gel spin coating route @ 2000 rpm. The Front contacts have been thermally evaporated in vacuum onto the organic layer at low pressure of 10-6 T, having a diameter of 1.5 mm and a thickness around 250 ± 10 nm. In this research, the electronic parameters of Au/PVP/p-Si/Al structures have been investigated. The obtained values indicate that the electronic parameters of the diode, like ideality factor (n), saturation current, barrier height (ΦB), and rectification coefficient (R) are respectively found to be (in dark) 2.2, 0.8 μA, 0.61 V, and 1.85×104. The open circuit voltage VOC is about 0.2 V. A non-diode ideal behavior is observed and ideality factor exceeds the unity (n>5). Consequently, VOC only depends on the solar cell material. We fabricate the device in the aim to use it in solar cell, photodiode and photoconductor applications.

Reactively Sputtered Cu2ZnTiS4 Thin Film as Low-Cost Earth-Abundant Absorber

Cu2ZnTiS4 thin films have been deposited on glass by the reactive cosputtering technique with high-purity ZnS and Cu and Ti metals as targets and H2S as reactive gas. Cu2ZnTiS4 thin films were obtained at various temperatures and H2S flows and were annealed in H2S atmosphere. The structural, morphological, and optical properties of the Cu2ZnTiS4 thin films were examined by scanning electron microscopy, energy-dispersive spectroscopy, x-ray diffraction (XRD) analysis, and ultraviolet–visible (UV–Vis) spectroscopy. Agglomeration was found to increase with increasing temperature. The XRD peaks of the Cu2ZnTiS4 thin films were consistent with those of Cu2ZnSnS4. Furthermore, the optical bandgaps of the Cu2ZnTiS4 films were lower than those of conventional Cu2ZnSnS4 thin films.

Influence of temperature and light intensity on Ru(II) complex based organic-inorganic device

An organic-inorganic junction was fabricated by forming [Ru(Cy2PNHCH2-C4H3O)(η6-p-cymene)Cl2] complex thin film using spin coating technique on n-Si and evaporating Au metal on the film. It was seen that the structure had perfect rectification property. Current-voltage (I-V) measurements were carried out in dark and under various illumination conditions (between 50-100 mW/cm2) and with the temperature range from 303 to 380 K. The structure showed unusually forward and reverse bias temperature and light sensing behaviors. It was seen that the current both in forward and reverse bias increased with the increase in light intensity and temperature.