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Öğe Eco-Friendly Boost for Perovskite Photovoltaics: Harnessing Cellulose-Modified SnO2 as a High-Performance Electron Transporting Material(Amer Chemical Soc, 2023) Ozkaya, Veysel; Sadegh, Faranak; Unal, Muhittin; Alkan, Bulent; Ebic, Murat; Ozturk, Teoman; Yilmaz, MucahitIn this study, a passivated tin oxide (SnO2) film is successfully obtained through the implementation of sodium carboxymethyl cellulose (Na-CMC) modifier agent and used as the electron transporting layer (ETL) within the assembly of perovskite solar cells (PSCs). The strategic incorporation of the Na-CMC modifier agent yields discernible enhancements in the optoelectronic properties of the ETL. Among the fabricated cells, the champion cell based on Na-CMC-complexed SnO2 ETL achieves a conversion efficiency of 22.2% with an open-circuit voltage (V-OC) of 1.12 V, short-circuit current density (J(SC)) of 24.57 mA/cm(2), and fill factor (FF) of 80.6%. On the other hand, these values are measured for the pristine SnO2 ETL-based control cell as V-OC = 1.11 V, J(SC) = 23.59 mA/cm(2), and FF = 76.7% with an efficiency of 20.1%. This improvement can be ascribed to the high charge extraction ability, higher optical transmittance, better conductivity, and decrease in the trap state density associated with the passivated ETL structure. In addition, the cells employing Na-CMC-complexed SnO2 ETL exhibit prolonged stability under ambient conditions during 2000 h. Based on the preliminary results, this study also presents a set of findings that could have substantial implications for the potential use of the Na-CMC molecule in both large-scale perovskite cells and perovskite/Si tandem configuration.Öğe Effect of in-/ex-situ annealing temperature on the optical, structural and gas sensing dynamics of CdS nanostructured thin films(Academic Press Ltd- Elsevier Science Ltd, 2020) Gormez, Arife Efe; Basyooni, Mohamed A.; Zaki, Shrouk E.; Eker, Yasin Ramazan; Sonmez, Erdal; Yilmaz, MucahitEffect of in-/ex-situ annealing on the structure, optical, photoluminescence, electrical characterization and gas sensing dynamics on CdS thin films are presented. Raman characterizations showed an increase in the peak intensity with increasing the annealing temperature under ex-situ, while a lower peak intensity observed through the in-situ annealing condition. No shift was observed in the Photoluminescence peaks through the yellow band peaks of in-situ annealed samples, however, a slightly blue shift was observed through the ex-situ annealed samples. High conductivity was observed for all samples, while in the case of in-situ RT, in-situ 100 degrees C, ex-situ 200 degrees C and ex-situ 300 degrees C, a CO2 and O-2 gas sensing activity have been tested. The ex-situ 300 degrees C sample shows a higher response towards CO2 compared with the ex-situ 200 degrees C film. While, both in-situ RT and 100 degrees C sensors show the same response towards CO2 with a high gas response. However, the in-situ 100 degrees C sensor has the highest response compared to in-situ RT film with a high response of 25% at 50 sccm towards O-2.Öğe Efficient MoWO3/VO2/MoS2/Si UV Schottky photodetectors; MoS2 optimization and monoclinic VO2 surface modifications(Nature Portfolio, 2020) Basyooni, Mohamed A.; Zaki, Shrouk E.; Shaban, Mohamed; Eker, Yasin Ramazan; Yilmaz, MucahitThe distinctive properties of strongly correlated oxides provide a variety of possibilities for modulating the properties of 2D transition metal dichalcogenides semiconductors; which represent a new class of superior optical and optoelectronic interfacing semiconductors. We report a novel approach to scaling-up molybdenum disulfide (MoS2) by combining the techniques of chemical and physical vapor deposition (CVD and PVD) and interfacing with a thin layer of monoclinic VO2. MoWO3/VO2/MoS2 photodetectors were manufactured at different sputtering times by depositing molybdenum oxide layers using a PVD technique on p-type silicon substrates followed by a sulphurization process in the CVD chamber. The high quality and the excellent structural and absorption properties of MoWO3/VO2/MoS2/Si with MoS2 deposited for 60 s enables its use as an efficient UV photodetector. The electronically coupled monoclinic VO2 layer on MoS2/Si causes a redshift and intensive MoS2 Raman peaks. Interestingly, the incorporation of VO2 dramatically changes the ratio between A-exciton (ground state exciton) and trion photoluminescence intensities of VO2/(30 s)MoS2/Si from < 1 to > 1. By increasing the deposition time of MoS2 from 60 to 180 s, the relative intensity of the B-exciton/Aexciton increases, whereas the lowest ratio at deposition time of 60 s refers to the high quality and low defect densities of the VO2/(60 s)MoS2/Si structure. Both the VO2/(60 s)MoS2/Si trion and A-exciton peaks have higher intensities compared with (60 s) MoS2/Si structure. The MoWO3/VO2/(60 s) MoS2/Si photodetector displays the highest photocurrent gain of 1.6, 4.32 x 10(8) Jones detectivity, and similar to 1.0 x 10(10) quantum efficiency at 365 nm. Moreover, the surface roughness and grains mapping are studied and a low semiconducting-metallic phase transition is observed at similar to 40 degrees C.Öğe Fast response of CO2 room temperature gas sensor based on Mixed-Valence Phases in Molybdenum and Tungsten Oxide nanostructured thin films(Elsevier Sci Ltd, 2020) Basyooni, Mohamed A.; Zaki, Shrouk E.; Ertugrul, Sezin; Yilmaz, Mucahit; Eker, Yasin RamazanMolybdenum - tungsten oxide (Mo1-xWxO3, x = 1, 0.8, and 0.6) nanostructured thin films-based room temperture (RT) gas sensors are prepared by means of reactive RF magnetron co-sputtering at 400 degrees C. The structural, morphology, topography, optical, and electrical characterizations of the prepared sensors are carried out by XRD Rietveld structure refinement analyses, SEM, AFM, UV-VIS spectrophotometer, and source meter. By controlling the deposition temperture of 400 degrees C, a co-existing phase of MoO3 and MoO2 in WO3 matrix is presented with high oxygen vacancies concentration as calculated from the XRD Rietveld Refinement analyses. By increasing the Mo content, the calculated oxygen vacancies concentration increases by factor of 1.36. The optical characterization of Mo0.2W0.6O3 thin film shows a high transparent of 99.6% at 500 nm. The prepared thin films have successfully tested to detect carbon dioxide (CO2) at RT (20 degrees C) with high selectivity and repeatability. The Mo0.4W0.6O3 sensor film shows an electrical Schottky contact with fast response and recovery times towards CO2 under UV light activation. Mo0.4W0.6O3 thin film under dark and UV conditions were able to detect low CO2 concentration of 2 and 0.5 sccm CO2 M RT, respectively. Under UV illumination, Mo0.4W0.6O3 film shows a fast response and recovery time of 6.53 and 8.05 sat 0.5 sccm with sensitivity of 29.19%. Under UV photonic activation, higher electron concentration is presented in the oxide surface, which leads to high probability for reaction with CO2 molecules, and consequently enhanced the chemisorption of CO2. The enhanced CO2 gas sensitivity and fast response may refer to the high oxygen vacancies concentration and the active role of the grain boundaries in MoO2, MoO3 and WO3 mixed-valence nanostructured under UV activation.Öğe Improving performance and stability in quantum dot-sensitized solar cell through single layer graphene/Cu2S nanocomposite counter electrode(Pergamon-Elsevier Science Ltd, 2020) Akman, Erdi; Altintas, Yemliha; Gulen, Mahir; Yilmaz, Mucahit; Mutlugun, Evren; Sonmezoglu, SavasIn this work, we presented an effective nanocomposite to modify the Cu2S film by employing single layer graphene (SLG) frameworks via chemical vapor deposition, and utilized this nanocomposite as counter electrode (CE) with CdSe/ZnS core/shell quantum dots for highly stable and efficient quantum dot-sensitized solar cell (QDSSC). Furthermore, Cu2S film is directly synthesized on SLG framework by electrodeposition method. Using this nanocomposite as CE, we have achieved the high efficiency as high as 3.93% with fill factor of 0.63, which is higher than those with bare Cu2S CE (3.40% and 0.57). This remarkable performance is attributed to the surface area enhancement by creating nanoflower-shape, the reduction of charge transfer resistance, improvement of catalytic stability, and the surface smoothness as well as good adhesion. More importantly, no visible color change and detachment from surface for the Cu2S@SLG nanocomposite was observed, demonstrating that the SLG framework is critical role in shielding the Cu2S structure from sulphur ions into electrolyte, and increasing the adhesion of the Cu2S structure on surface, thus preventing its degradation. Consequently, the Cu2S@SLG nanocomposite can be utilized as an effective agent to boost up the performance of QDSSCs. (c) 2019 Elsevier Ltd. All rights reserved.Öğe Molybdenum disulfide thin films fabrication from multi-phase molybdenum oxide using magnetron sputtering and CVD systems together(Academic Press Ltd- Elsevier Science Ltd, 2020) Karatas, Ayse; Yilmaz, MucahitMolybdenum disulfide (MoS2) is a layered 2D semiconducting material with a tunable bandgap and a promising materials for next generation optoelectronics applications. In this study, the characterization of large-scale MoS2 films obtained by sulfurization of Mo-O films grown in different thicknesses with reactive magnetron sputtering method at 400 degrees C are reported. At a critical deposition temperature of 400 degrees C, different phases of Mo-O structure with high photoluminescent and bandgap were observed. Although there are no triangular domains, bandgaps and PL properties are close to few-layered MoS2. The enhanced PL intensities attributed to the increasing amount of MoO2 that may cause MoS2's folding and the large number of electrons from MoO2 in the MoO2-MoS2 hetero-structure. The UV-VIS spectroscopy analysis shows that two bandgaps are presented with a low and high values which may extend a wide absorption range. One of these bandgaps is compatible with few-layer MoS2s and the other increases by the thickness of the Mo-O film grown by magnetron sputtering. This explains the absorption at low wavelengths, but also shows that the MoO2 structure can be used to adjust the band gaps of MoSs. The combined growth technique of magnetron sputtering and CVD is provided a high quality and homogeneous MoS2 thin films for next-generation optoelectronics and nanoelectronic devices, as well as for other potential applications.Öğe MoO3 nanowire growth on VO2/WO3 for thermochromic applications(Royal Soc Chemistry, 2024) Houimi, Amina; Kabatas, Mohamed A. Basyooni-M.; Yilmaz, Mucahit; Eker, Yasin RamazanThis study explores the structural, electronic, and optical properties of sandwich-structured thin films composed of WO3, MoWO3, and MoO3 as window layers on VO2/WO3 via a physical vapor deposition method. Morphological analysis demonstrates the evolution of distinct nanowires, offering insights into the lattice strain of the VO2 layer toward high-performance thermochromatic devices. Temperature-dependent sheet resistivity is investigated, showcasing significant improvements in conductivity for samples with MoO3 as a window layer. The electrical and optical properties of the MoO3/VO2/WO3 device showed a phase transition temperature (T-c) of 36.8 degrees C, a transmittance luminous (T-lum) of 54.57%, and a solar modulation ability (Delta T-sol) of 12.43. This comprehensive analysis contributes to understanding the growth of nanowires on multi-layered thin films, offering valuable insights into potential applications in bright windows.Öğe Nanostructured MoS2 and WS2 Photoresponses under Gas Stimuli(Mdpi, 2022) Basyooni, Mohamed A.; Zaki, Shrouk E.; Alfryyan, Nada; Tihtih, Mohammed; Eker, Yasin Ramazan; Attia, Gamal F.; Yilmaz, MucahitThis study was on the optoelectronic properties of multilayered two-dimensional MoS2 and WS2 materials on a silicon substrate using sputtering physical vapor deposition (PVD) and chemical vapor deposition (CVD) techniques. For the first time, we report ultraviolet (UV) photoresponses under air, CO2, and O-2 environments at different flow rates. The electrical Hall effect measurement showed the existence of MoS2 (n-type)/Si (p-type) and WS2 (P-type)/Si (p-type) heterojunctions with a higher sheet carrier concentration of 5.50 x 10(5) cm(-2) for WS2 thin film. The IV electrical results revealed that WS2 is more reactive than MoS2 film under different gas stimuli. WS2 film showed high stability under different bias voltages, even at zero bias voltage, due to the noticeably good carrier mobility of 29.8 x 10(2) cm(2)/V. WS2 film indicated a fast rise/decay time of 0.23/0.21 s under air while a faster response of 0.190/0.10 s under a CO2 environment was observed. Additionally, the external quantum efficiency of WS2 revealed a remarkable enhancement in the CO2 environment of 1.62 x 10(8) compared to MoS2 film with 6.74 x 10(6). According to our findings, the presence of CO2 on the surface of WS2 improves such optoelectronic properties as photocurrent gain, photoresponsivity, external quantum efficiency, and detectivity. These results indicate potential applications of WS2 as a photodetector under gas stimuli for future optoelectronic applications.Öğe Role of oxygen vacancies in vanadium oxide and oxygen functional groups in graphene oxide for room temperature CO2 gas sensors(Elsevier Science Sa, 2019) Zaki, Shrouk E.; Basyooni, Mohamed A.; Shaban, Mohamed; Rabia, Mohamed; Eker, Yasin Ramazan; Attia, Gamal F.; Yilmaz, MucahitThe greenhouse effect is involving global heating and climate change within the world. Carbon dioxide (CO2) is one of the major gas at the origin of this effect, but also the byproduct of human activity. Therefore, monitoring the indoor/outdoor CO2 emission by gas sensors is one of the priorities for environmental preservation. In this paper, the sensing performance of CO2 towards two different O-rich films have been studied; graphene oxide (GO) and vanadium dioxide (VO2). The preparation of GO film has been carried out by spray pyrolysis on fluorine tin oxide (FTO) prepared by the modified Hummers method. While the VO2 film has been sol-gel spin-coated on a glass substrate. Both films have been characterized using XRD, SEM and electrical properties. The CO2 gas sensing mechanism and the role of oxygen vacancies in VO2 are addressing. The oxygen functional groups in GO play a main role in the CO2 gas the sensitivity level and response time. Their gas sensing performances have been investigated based on measuring the response vs recovery time, dynamic response curve analysis and sensitivity. In order to better understand the sensing mechanism, characterization has been done with different gas concentrations. Both GO and VO2 based CO2-sensors are acted as an n-type sensor. Sensing behavior of GO at RT has explained to be mainly mediated by the oxygen functional groups and a wide range of active sites. In the other hand, VO2 contains oxygen vacancies and more defect sites which play a main role in the RT sensing activity and low recovery time. (C) 2019 Elsevier B.V. All rights reserved.Öğe Screen printable fire through nickel contacts for silicon solar cells(Elsevier, 2023) Akgayev, Berkeli; Sezgin, Aysegul; Yilmaz, Mucahit; Unsur, VeyselMetallization of crystalline silicon (Si) solar cells is indispensable for reducing the cost while increasing the overall efficiency. Developing alternative materials to the most commonly used screen printed silver (Ag) contacts is a critical factor. Here, in this study, a nickel (Ni) metal paste consisting of Ni metal particles, glass frit and an organic vehicle is fabricated for screen printed Ni contacts. To prevent possible Schottky barrier formation, a graphene layer is placed on the front surface of the Si solar cell between Ni and Si forming a metal-2Dsemiconductor structure ensuring the ohmic (or ohmic-like) contacts. It is demonstrated here that the graphene is transferred successfully onto the textured front surface of the cells and G/2D peaks are observed clearly, indicating the good quality of the graphene layer. Constituents of Ni metal paste, glass frit and organic vehicle, are fabricated in concordance with nickel metal powder and mixed to achieve optimal electrical output parameters. The findings suggest that the transition temperature of the glass frit is between 270 degrees C and 300 degrees C resulting in around 475 degrees C softening temperature, which gives excellent etching behavior to the paste. The average contact resistance of the screen printed Ni contacts governed by etching process is measured around 6.9 m & omega; cm2. The SEM images of the contacts show a uniform distribution and sintering behavior similar to that of silver counterparts. The light current-voltage measurements read the open circuit voltage of 660 mV, the short circuit density of 39.11 mA/cm2 and the fill factor of 81.4% resulting in around 21% efficiency.Öğe Structural, optical, electrical and room temperature gas sensing characterizations of spin coated multilayer cobalt-doped tin oxide thin films(Academic Press Ltd- Elsevier Science Ltd, 2020) Basyooni, Mohamed A.; Eker, Yasin Ramazan; Yilmaz, MucahitThe negative charge trapped in the oxygen species present in metal oxides like Tin Oxide (SnO2) caused an upward band bending and makes these materials as promising sensing materials for CO2 detection. However, sensors based on pure SnO2 may only detect CO2 at high temperature making them un-sensitive at room temperature (RT) (20 degrees C). In this study, SnO2 and Cobalt doped SnO2 (Co:SnO2) thin films of varying thickness were successfully synthesized by sol-gel spin coating technique, followed by annealing. The highly active surface due to high number of divided layers has been determined by X-ray diffraction (XRD) for neat and doped SnO2 deposition. Moreover, the effect of increasing the annealing from 400 to 500 degrees C has been evaluated. The calculated band gap of the multilayer sample annealed at 500 degrees C blue shifted from 3.55 to 3.81 eV with the Co doping. Therefore, the Co doped SnO2 can detect CO2 as low as 30 vol% in atmosphere at RT, meanwhile the un-doped SnO2 coating shows a weak response. Moreover, at high CO2 concentration the recovery time decreases due to the high desorption kinetic. The obtained results illustrate the control of the film's properties gives the opportunity to manage the sensing and optoelectronic performance.Öğe Tuning the Metal-Insulator Transition Properties of VO2 Thin Films with the Synergetic Combination of Oxygen Vacancies, Strain Engineering, and Tungsten Doping(Mdpi, 2022) Basyooni, Mohamed A.; Al-Dossari, Mawaheb; Zaki, Shrouk E.; Eker, Yasin Ramazan; Yilmaz, Mucahit; Shaban, MohamedVanadium oxide (VO2) is considered a Peierls-Mott insulator with a metal-insulator transition (MIT) at T-c = 68 degrees C. The tuning of MIT parameters is a crucial point to use VO2 within thermoelectric, electrochromic, or thermochromic applications. In this study, the effect of oxygen deficiencies, strain engineering, and metal tungsten doping are combined to tune the MIT with a low phase transition of 20 degrees C in the air without capsulation. Narrow hysteresis phase transition devices based on multilayer VO2, WO3, Mo0.2W0.8O3, and/or MoO3 oxide thin films deposited through a high vacuum sputtering are investigated. The deposited films are structurally, chemically, electrically, and optically characterized. Different conductivity behaviour was observed, with the highest value towards VO1.75/WO2.94 and the lowest VO1.75 on FTO glass. VO1.75/WO2.94 showed a narrow hysteresis curve with a single-phase transition. Thanks to the role of oxygen vacancies, the MIT temperature decreased to 35 degrees C, while the lowest value (T-c = 20 degrees C) was reached with Mo0.2W0.8O3/VO2/MoO3 structure. In this former sample, Mo0.2W0.8O3 was used for the first time as an anti-reflective and anti-oxidative layer. The results showed that the MoO3 bottom layer is more suitable than WO3 to enhance the electrical properties of VO2 thin films. This work is applied to fast phase transition devices.Öğe The variation of the features of SnO2 and SnO2:F thin films as a function of V dopant(Springer, 2014) Turgut, Guven; Sonmez, Erdal; Yilmaz, Mehmet; Cogenli, M. Selim; Yilmaz, Mucahit; Turgut, Umit; Dilber, RefikV doped SnO2 and SnO2:F thin films were successfully deposited on glass substrates at 500 A degrees C with spray pyrolysis. It was observed that all films had SnO2 tetragonal rutile structure and the preferential orientation depended on spray solution chemistry (doping element and solvent type) by X-ray diffraction measurements. The lowest sheet resistance and the highest optical band gap, figure of merit, infrared (IR) reflectivity values of V doped SnO2 for ethanol and propane-2-ol solvents and V doped SnO2:F films were found to be 88.62 abroken vertical bar aEuro3.947 eV-1.02 x 10(-4) abroken vertical bar(-1)-65.49 %, 65.35 abroken vertical bar aEuro3.955 eV-8.54 x 10(-4) abroken vertical bar(-1)-72.58 %, 5.15 abroken vertical bar aEuro4.076 eV-6.15 x 10(-2) abroken vertical bar(-1)-97.32 %, respectively, with the electrical and optical measurements. Morphological properties of the films were investigated by atomic force microscope and scanning electron microscope measurements. From these analysis, the films consisted of nanoparticles and the film morphology depended on doping ratio/type and solvent type. It was observed pyramidal, polyhedron, needle-shaped and spherical grains on the films' surfaces. The films obtained in present study with these properties can be used as front contact for solar cells and it can be also one of appealing materials for other optoelectronic and IR coating applications.
