Savaş Sönmezoğlu

High-efficiency dye-sensitized solar cells using ferrocene-based electrolytes and natural photosensitizers

A new and promising dye-sensitized solar cell (DSSC) bilayer design was developed using an Fe2+/Fe3+ (ferrocene) liquid electrolyte and natural dyes extracted from Hypericum perforatum, Rubia tinctorum L. and Reseda luteola. The photovoltaic parameters controlling the device performance were then investigated. A DSSC based on quercetin dye displayed the most efficient solar to electricity conversion efficiency compared with other dyes with a maximum η value of 2.17%. Maximum overall conversion efficiencies under simulated sunlight that was comparable to natural photosynthesis were increased by 15%. The identification of appropriate additives for improving VOC without causing dye degradation may result in further enhancement of cell performance, making the practical application of such systems more suitable for achieving economically viable solar energy devices.

Preparation of MIP-based QCM nanosensor for detection of caffeic acid.

In the present work, a new caffeic acid imprinted quartz crystal microbalance (QCM) nanosensor has been designed for selective assignation of caffeic acid in plant materials. Methacrylamidoantipyrine-iron(III) [MAAP-Fe(III)] as metal-chelating monomer has been used to prepare selective molecular imprinted polymer (MIP). MIP film for detection of caffeic acid has been developed on QCM electrode and selectivity experiments and analytical performance of caffeic acid imprinted QCM nanosensor has been studied. The caffeic acid imprinted QCM nanosensor has been characterized by AFM. After the characterization studies, imprinted and non-imprinted nanosensors was connected to QCM system for studies of connection of the target molecule, selectivity and the detection of amount of target molecule in real samples. The detection limit was found to be 7.8 nM. The value of Langmuir constant (b) (4.06 × 10(6)) that was acquired using Langmuir graph demonstrated that the affinity of binding sites was strong. Also, selectivity of prepared caffeic acid imprinted nanosensor was found as being high compared to chlorogenic acid. Finally, the caffeic acid levels in plant materials was determined by the prepared QCM nanosensor.

The effects of film thickness on the optical properties of TiO2?SnO2 compound thin films

In this work, TiO2?SnO2 compound thin films was synthesized by the sol?gel technique, and the effects of film thickness on the optical and structural properties of these thin films were investigated. Optical constants such as the refractive index, extinction coefficient, dielectric constant and third-order optical nonlinear susceptibility were determined from the measured transmittance spectra in the wavelength range 300?1500?nm using the envelope method. Meanwhile, the dispersion behavior of the refractive index was studied in terms of the single-oscillator Wemple?DiDomenico (W?D) model, and the physical parameters of the refractive index dispersion parameter and the dispersion energy were found. Furthermore, the optical band gap values were calculated by the W?D model and the Tauc model, respectively. It is observed that the values obtained from the W?D model are in quite good agreement with those determined from the Tauc model. Important changes in optical and dielectric constants were observed by means of variation in film thickness. To examine the structure of the thin films, x-ray diffraction (XRD) methods were used. Combined with XRD analysis, the observed variations in both the refractive index and optical band gap are directly correlated with the structural evolution of the composite TiO2?SnO2 thin films. The most significant results of the present study are that the thickness of the film can be used to modify the optical, structural and dielectric properties of TiO2?SnO2 thin films.

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.

Investigation of the photoinduced electron injection processes for natural dye-sensitized solar cells: the impact of anchoring groups

In this study, nine different natural dyes having various anchoring groups were extracted from various plants and used as photo-sensitizers in DSSC applications. The photovoltaic parameters controlling the cell performance were investigated and the results were discussed as a function of anchoring groups. The obtained power conversion efficiencies (PCEs) vary from 0.18 to 1.87%, while the quantum yields are heavily dependent on both the anchoring group and type of pigments. Moreover, the effects of anchoring groups on the photoinduced electron injection dynamics from natural dye molecules to TiO2 nanoparticles were studied using time resolved fluorescence spectroscopy measurements. In these dyes, the long-hydroxyl & carbonyl-chain bearing anthocyanin, with the maximum electron transfer rate (kET), has shown the best photosensitization effect with regard to cell output. Despite the fact that their performance in DSSCs is somewhat lower or close to the metal complexes, these metal-free natural dyes can be treated as a new generation of sensitizers.

Fabrication and electrical characterization of pyrrole–aniline copolymer-based Schottky diodes

In this work, pyrrole–aniline copolymer/p-Si structure has been fabricated by forming a thin organic copolymer film on a p-Si wafer. A good rectifying behavior was seen from the current–voltage (I–V) characteristics. The characteristic parameters of the structure such as barrier height, ideality factor, interface states density and series resistance were determined from the electrical measurements using I–V, Cheungs, and modified Nordes function. The calculated barrier height values from different methods have shown the consistency of the approaches. The obtained ideality factor which is greater than unity refers to the deviation from ideal diode characteristics. This deviation can be attributed to secondary mechanisms, which include interface dipoles due to interface doping or specific interface structure, as well as fabrication-induced defects at the interface. The energy distribution of interface-state density of the copolymer-based structure was determined, and the interface-state density was found to vary from 1.27 × 1016 cm−2 eV−1 in (0.07 – Ev) eV to 2.45 × 1015 cm−2 eV−1 in (0.52 – Ev) eV. Furthermore, these copolymers were characterized with UV–vis, FTIR techniques, and thermal analysis.

Influence of annealing temperature on structural, morphological and optical properties of nanostructured TiO2 thin films

Abstract Thermal annealing is widely used to improve crystal quality, which affects electrical and structural properties by reducing study defects in materials. Therefore, enormous research efforts were focused on the control of material surface nanostructure through annealing processes, which is of interest for various technologies. However, no work providing a detailed explanation for the structural, morphological and optical parameters of nanostructured TiO2 thin films deposited on glass at temperature above 500°C by the sol–gel dip coating method has been presented to date. In this work, we have grown nanostructured TiO2 thin films by sol–gel dip coating method on glass substrates at room temperature and studied the effects of annealing temperature from 200 to 700°C on optical performance, microstructural changes and surface morphology evolution. The results of this work may be summarised as follows: the X-ray diffraction results show that annealed TiO2 thin films have anatase crystal structure, and the intensities of the peaks of the crystalline phase increased with the increase in annealing temperature; from atomic force microscopy images, distinct variations in morphology of the thin films were also observed; and optical results show that TiO2 films exhibit high visible transmittance, and it has a maximum transmittance of ∼93·61% at 500°C annealing temperature. The optical band gap of the as grown thin films decreases from 3·68 to 3·31 eV with the increase in annealing temperatures. The TiO2 thin film annealed at 500°C has the best optical property. The change in structural, morphological and optical properties with annealing temperature demonstrates that this material has a potential to be used as a novel technology such as nanoelectronics and possibly nano-optoelectronic devices based on nanomaterial for insulating, semiconducting and electron and/or hole blocking layer, etc.

Development of a highly sensitive MIP based-QCM nanosensor for selective determination of cholic acid level in body fluids

Determination of cholic acid is very important and necessary in body fluids due to its both pharmaceutical and clinical significance. In this study, a quartz crystal microbalance (QCM) nanosensor, which is imprinted cholic acid, has been developed for the assignation of cholic acid. The cholic acid selective memories have been generated on QCM electrode surface by using molecularly imprinted polymer (MIP) based on methacryloylamidohistidine-copper (II) (MAH-Cu(II)) pre-organized monomer. The cholic acid imprinted nanosensor was characterized by atomic force microscopy (AFM) and then analytical performance of the cholic acid imprinted QCM nanosensor was studied. The detection limit was found to be 0.0065μM with linear range of 0.01-1,000 μM. Moreover, the high value of Langmuir constant (b) (7.3*10(5)) obtained by Langmuir graph showed that the cholic acid imprinted nanosensor had quite strong binding sites affinity. At the last step of this procedure, cholic acid levels in body fluids were determined by the prepared imprinted QCM nanosensor.

Exploring on Photovoltaic Performance of Dye-Sensitized Solar Cells Using Polyaniline as a Counter Electrode: Role of Aluminum-Solvent Interactions

In this work, we successfully synthesized aluminum-doped polyaniline in various solvent media using chemical oxidation polymerization, and for the first time, investigated their applications as counter electrode (CE) in dye-sensitized solar cells (DSSCs). The experimental results (field emission scanning electron microscopy/energy dispersive X-ray analysis, atomic absorption spectrometer, Fourier transform infrared spectroscopy, thermogravimetric/differential thermal analysis, etc.) showed that critical properties such as crystallinity, conductivity, and surface area of PAni polymers can be controlled through both Al ions and/or solvent media. The photovoltaic performance of DSSCs was evaluated by current density–voltage (J–V) and external quantum efficiency measurements. The differences in the conversion efficiencies (η) were explained based on the electrocatalytic abilities and electron transfer properties of CEs. Of the CEs in various solvents, the P@6 CE in acetone showed the best electrocatalytic ability and highest η of 5.97%. This is even higher than that of the cell with Pt CE (5.75%). Furthermore, its stability under a prolonged irradiation is somewhat lower or close to the Pt CE, P@6 CE based DSSC showed the characteristics of rapid activity onset, high multiple start/stop capability, and superior irradiation stability. This novel concept—along with promising electrocatalytic activity and facile electron transfer—provides a new approach to enhance the photovoltaic performances of Pt-free DSSCs.

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.