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Öğe CZTS tabanlı ince film güneş hücrelerine grafen entegrasyonu(Niğde Ömer Halisdemir Üniversitesi, 2024) Erkan, Serkan; Zan, Recep; Olğar, Mehmet AliTez kapsamında, saçtırma sistemi kullanılarak Mo, Ni ve Cu folyolar üzerine Altlık/ZnS/CuSn/Cu yapısı üretilmiş ve Hızlı Tavlama Sistemi (RTP) ile Mo, Ni ve Cu folyolar için sırasıyla 550 °C, 425 °C ve 425 °C optimize edilen sıcaklıklarda sülfürlenerek CZTS filmler elde edilmiştir. Esnek-folyo/CZTS/CdS/i-ZnO/ITO/Al yapısı kullanılarak üretilen güneş hücrelerinde en yüksek hücre verimi %3.26 ile Mo-folyo/CZTS yapısından elde edilmiştir (Hücre-I). Ayrıca, CVD yöntemiyle Mo, Ni ve Cu folyolar üzerinde farklı katman sayılarında katkısız, N2-katkılı (NKGr) ve B2H6-katkılı (Diboran katkılı) (DKGr) grafen filmler sentezlenmiş ve yapılan karakterizasyonlar sonucunda Mo ve Cu folyolar üzerinde tek (TKGr) ve birkaç katmanlı (BKGr), Ni folyolar üzerinde ise birkaç ve çok katmanlı (ÇKGr) grafen filmlerin başarılı bir şekilde sentezlendiği belirlenmiştir. Tez kapsamında, yapılan grafen entegrasyonu ile Mo-folyo/BKGr/CZTS/CdS/i-ZnO/ITO/Al ve Ni-folyo/ÇKGr/CZTS/CdS/i-ZnO/ITO/Al yapısından sırasıyla %3.72 ve %2.3 (Hücre-II), Mo-folyo/BKGr/CZTS/CdS/i-ZnO/80nmITO/BKGr/Al yapısından %7.8 (Hücre-III), Mo-folyo/DKGr/CZTS/CdS/i-ZnO/80nmITO/BKGr/Al yapısından %8.57 (Hücre-IV) ve Mo-folyo/DKGr/CZTS/CdS/i-ZnO/80nmITO/NKGr/Al yapısından %9.0 hücre verimi elde edilmiştir.Öğe Enhanced photovoltaic performance of silicon-based solar cell through optimization of Ga-doped ZnO layer(Iop Publishing Ltd, 2023) Erkan, Serkan; Altuntepe, Ali; Yazici, Duygu; Olgar, Mehmet Ali; Zan, RecepIn the present study, the impact of deposition pressure and substrate temperature of Ga-doped Zinc Oxide (GZO) thin film and the photovoltaic performance of this structure as a transparent conductive oxide (TCE) layer in silicon-based solar cell were investigated. Implementing a single target of GZO, the structural, optical, and electrical properties of 350 nm thick GZO thin films with various deposition pressure (5 mTorr, 10 mTorr, 15 mTorr and 20 mTorr) at room temperature (RT) and substrate temperature (RT, 150 degrees C, 200 degrees C, 250 degrees C) at 15 mTorr deposition pressure were fabricated using RF magnetron sputtering technique. The aim here was to find out the GZO films with the optimum pressure and substrate temperature to incorporate them into solar cell as a TCE layer. The X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques were used to determine the structural properties of all samples. The optical transmission measurements were performed using spectroscopic Ellipsometer and the band gap values were calculated by Tauc plot using optical transmission data. In addition, the electrical characterization of the GZO samples were analyzed by the Van der Pauw method and Hall measurements. Finally, the most promising GZO thin film was determined based on the structural and optoelectrical characterization. The findings indicated that the XRD pattern of all the prepared films was dominated by (002) preferential orientation irrespective of the deposition pressure and substrate temperature. The AFM measurements showed that all the samples had a dense surface morphology regardless of the deposition pressures, but the surface morphology of the samples was clearly changed upon increasing substrate temperatures. The transmission values of the film did not significantly alter (similar to 82%) when the deposition pressures except for the substrate temperature of 200 degrees C (86%) were changed. The band gap values were calculated between 3.30 eV and 3.36 eV, which can be associated with enhancement of crystalline quality of the films. The lowest resistivity and the highest carrier concentration values belonged to the film fabricated at 15 mTorr@200 degrees C by 2.0 x 10-3 omega.cm and 1.6 x 1020 cm-3, respectively. Both increasing the deposition pressure (up to 15 mTorr) and substrate temperature (up to 200 degrees C) contributes to improving the crystallite size, widening the optical band gap, lowering the resistivity, and increasing the carrier concentration. In order to evaluate and compare the effect of both deposition pressure and substrate temperature, Silicon-based solar cells were fabricated using the most promising layers (15 mTorr@RT, 15 mTorr@200 degrees C). The cell performance with the GZO thin film as a TCE layer showed that varying both the pressure and substrate temperature of the GZO film contributed to enhancing the solar cell parameters. Thus, the conversion efficiency increased from 9.24% to 12.6% with the sequential optimization of pressure and temperature. It can be concluded that the pressure applied during the deposition and substrate temperature had a significant impact on the properties of GZO thin films and its photovoltaic performance of solar cell used as TCE layer.Öğe Hybrid transparent conductive electrode structure for solar cell application(Pergamon-Elsevier Science Ltd, 2021) Altuntepe, Ali; Olgar, Mehmet Ali; Erkan, Serkan; Hasret, Onur; Kececi, Ahmet Emin; Kokbudak, Gamze; Tomakin, MuratThis study draws on our experiences with graphene to perform a hybrid TCO structure composed of AZO and graphene. We first set out to enhance the electrical and optical properties of AZO to enable its use especially in the field of solar cell. Hence, in our study, we deposited various thicknesses of AZO thin films on glass substrates and transferred single layer graphene on them to realize the formation of hybrid TCO structure. Among the various AZO film thicknesses, the optimum one, 300 nm, was determined and then the graphene film was added on top of the AZO film. This hybrid structure was applied to the silicon based heterojunction solar cell with the idea of improving the cell performance. The cell performance fabricated using AZO film and AZO + graphene structure was analyzed using solar simulator. Our findings highlight the fact that the presence of graphene improved the cell efficiency by about 7%. Our research was further extended using ITO and ITO + graphene hybrid structure as TCO for silicon-based solar cell. We discovered that graphene incorporation increased the cell efficiency by almost 12% based on our results with ITO + graphene hybrid TCO structure on a similar cell. (c) 2021 Elsevier Ltd. All rights reserved.Öğe Hydrogen storage capacity of two-dimensional MoS2(Pergamon-Elsevier Science Ltd, 2024) Altuntepe, Ali; Erkan, Serkan; Olgar, Mehmet Ali; Celik, Selahattin; Zan, RecepHydrogen storage holds a crucial place for the future of the world in terms of green energy. Two-dimensional materials, in particular, are important in this regard. The aim of this study is to evaluate the performance of MoS2 which is one of the most popular member of two-dimensional materials family. To do this, bulk and exfoliated MoS2 were used. Firstly, the liquid phase exfoliation method was employed to obtain exfoliated MoS2 layers. Then, the hydrogen storage potential of the bulk and exfoliated MoS2 was addressed under 1, 3, 5, 7, and 9 bar hydrogen pressure. After the absorption process, all the samples were characterized using XRD, Raman Spectrometer, and BET ahead of evaluating their hydrogen storage potential. The XRD pattern showed that the peak positions of bulk and exfoliated MoS2 were not affected critically by hydrogen storage. In the Raman spectra, the A1g and E2g 1 peaks of all hydrogenated materials shifted to low wavelengths. Moreover, the BET measurements revealed that the specific surface area and the pore size of the bulk MoS2 were 12.31 m2/g and <= 67.46 nm respectively. Additionally, the specific surface area and the pore size of the exfoliated MoS2 were 23.16 m2/g and <= 69.28 nm, respectively. The hydrogen storage potential of the bulk and the exfoliated MoS2 was evaluated through an MFC in sccm unit. The bulk and exfoliated MoS2 stored 220 and 450 sccm hydrogen, respectively. Besides, the weight percent hydrogen storage for H-MoS2 and H -exfoliated MoS2 was determined to be 1.2 and 2.4 wt%, respectively. In summary, this study has shown that exfoliated MoS2, one of the twodimensional materials, can play a critical role for hydrogen storage due to their high specific surface area.Öğe Investigating surface area and hydrogen pressure effects on LiH and NaH(Academic Press Inc Elsevier Science, 2024) Altuntepe, Ali; Erkan, Serkan; Olgar, Mehmet Ali; Celik, Selahattin; Zan, RecepNaH and LiH are theoretically capable of storing hydrogen, but several challenges remain to be overcome before they can be widely used for hydrogen storage. In this study, LiH and NaH were ball-milled and the effect of surface area and hydrogen pressure on hydrogen storage capacity was investigated using the solid-state hydrogen storage method. XRD patterns and Raman spectra show significant shifts in main peak positions of LiH and NaH after hydrogen adsorption. BET analysis shows a significant increase in the specific surface area of LiH and NaH from 6.25 m(2)/g to 12.35 m(2)/g and from 1.34 m(2)/g to 2.33 m(2)/g respectively due to ball milling. The FTIR spectra showed more bonds in the 400-1200 cm(-1) fingerprint region after storing hydrogen in LiH and NaH. This suggests structural changes with enhanced bond bending due to hydrogen. At 9 bar pressure, LiH and NaH exhibited excellent hydrogen storage, with ball-milled LiH reaching about 3.55 wt% and 652 sccm, and NaH achieving approximately 1.58 wt% and 291 sccm. These results highlight the significant influence of surface area and hydrogen pressure on hydrogen storage potential. Incorporating the storage potential within the evaluation of PEM fuel cell performance, we suggest that an increased storage capacity directly corresponds to an augmented power density. The analysis of power density over time revealed that the hydrogen adsorbed ball-milled LiH exhibited the highest power density, peaking at 0.075 Wcm(-2) over the long term. In contrast, LiH displayed a lower power density (0.025 Wcm(-2)) while maintaining its long-term performance. The hydrogen adsorbed NaH and hydrogen adsorbed ball-milled NaH displayed power densities 0.050 Wcm(-2) and 0.073 Wcm(-2), respectively, but they showed short-term performance.Öğe Nitrogen Doped Graphene Film Synthesis and Characterization(Gazi Univ, 2022) Zan, Recep; Altuntepe, Ali; Erkan, Serkan; Seyhan, AyseHaving a single atom thickness formed by the combination of carbon atoms in a hexagonal mesh, graphene has been one of the most intensely researched areas in recent years. This is especially due to its wide range of uses thanks to its numerous superior properties such as high electrical and thermal conductivity, high light transmittance, high strength and large surface area. Despite these superior properties, graphene's high sheet resistance and lack of energy band gap limit its use in optoelectronic applications. Yet, these disadvantages can be overcome by implementing doping to the graphene structure. However, although the doping selection and synthesis method are very important in the doped graphene synthesis process, the permanence and homogeneity of the doping is even more critical. In this study, the synthesis and characterization of pure and nitrogen-doped graphene were carried out on copper foil using CVD system. Pyridine was used for the synthesis of the doped graphene, as a carbon and nitrogen source. We found out that the use of the CVD technique allows both homogeneous and permanent doping. In addition to pyridine, in the present study, the film thickness was also optimized by providing a low amount of methane gas flow to the CVD system during the synthesis. To enable the characterization of doped films, Raman spectroscopy, Energy Dispersive X-ray spectroscopy and Xray photo electron spectroscopy techniques were used, and the film quality, thickness, homogeneity, doping rate and type were determined.Öğe Nitrogen doped single layer graphene for CZTS-based thin film solar cells(Elsevier, 2024) Olgar, Mehmet Ali; Erkan, Serkan; Altuntepe, Ali; Zan, RecepCdS thin films are commonly utilized as a buffer layer in chalcopyrite thin-film solar cells. However, due to the toxic nature of Cadmium (Cd), ongoing efforts are being directed towards exploring alternative options. In this contribution, doped graphene film with remarkable optical and electrical properties has been introduced for the first time as an alternative buffer layer, replacing CdS in CZTS thin-film solar cell application. In this study, nitrogen-doped graphene (N-doped graphene) film was utilized as a substitute buffer layer in the CZTS thin-film solar cell structure, replacing the conventional CdS thin film. For comparative analysis, CZTS/N-doped graphene and CZTS/CdS traditional solar cell structures were fabricated and separately characterized. The CZTS thin films produced were examined through EDX, XRD, SEM, Raman, optical transmission and PL spectroscopy measurements. According to performed analyses, the Cu-poor and Zn-rich kesterite CZTS thin films exhibited a uniform and dense polycrystalline microstructure as observed in surface and cross-sectional SEM images. XRD spectra of the kesterite CZTS thin film displayed predominant peaks corresponding to the (112), (220/204), and (312/116) diffraction planes of the kesterite CZTS phase. Raman spectra showed a dominant peak at similar to 336 cm (-1) associated with the kesterite CZTS phase. PL emission spectra indicated transitions from the conduction band to defect levels. The CVD-grown doped graphene film exhibited a 3.43 I-2D/I-G ratio and a 25 cm (-1) FWHM of the 2D peak, indicating a single -layer graphene according to Raman analysis. Permanent nitrogen doping with a 2% atomic concentration was confirmed by XPS measurement. The optical transmission measurement of the single layer doped graphene film showed a 95% transmittance value. Nitrogen doping was contributed to decrease the sheet resistance of the graphene film. The Glass/Mo/CZTS/N-doped graphene/i-ZnO/ITO/Al solar cell displayed a V-OC of 0.267 V, J(SC) of 24.6 mA/cm(2), FF of 36.46, and eta of 2.37%, showing higher FF and Jsc values but lower conversion efficiency compared to the Glass/Mo/CZTS/CdS/i-ZnO/ITO/Al traditional solar cell structure. Hence, the superior working function and transparency properties position the N-doped graphene film as a competitive buffer layer for use in CZTS-based thin-film solar cells.Öğe Performance of Si-based solar cell utilizing optimized Al-doped ZnO films as TCO layer(Springer, 2023) Altuntepe, Ali; Erkan, Serkan; Hasret, Onur; Yagmyrov, Atajan; Yazici, Duygu; Tomakin, Murat; Olgar, Mehmet AliAluminum-doped zinc oxide (AZO) is one of the most popular transparent conducting oxide layers that can be employed in many optoelectronic applications in particular in photovoltaic devices due to being a low-cost and nontoxic material. In this study, we report on the effect of deposition pressure and substrate temperature on the properties of AZO films and solar cell performance by employing the optimized films. This study consists of two stages, the first of which concerns the optimization deposition pressure while the second is the substrate temperature of AZO films by evaluating the structural, optical, and electrical properties of the films. The deposited AZO thin film under 10 mTorr deposition pressure exhibited high optical transmission (89.9%), low electrical resistivity (9.1 x 10(-2) omega.cm), and high carrier concentration (3.74 x 10(19) cm(-3)) among the others. The impact of substrate temperature was then investigated using this deposition pressure at room temperature, 150, 200, and 250 ?. The deposited AZO films at 150 ? temperature were found to possess the highest optical transmission (91.1%), lowest resistivity (9.9 x 10(-4) omega.cm), and highest carrier concentration (1.1 x 10(20) cm(-3)) values. Hence, the 10 mTorr deposition pressure and 150 ? substrate temperature were selected as the optimum growth parameters to obtain AZO films, which were then employed in the cell structure. It was, thus, revealed that utilizing AZO films in silicon-based solar cell using such parameters led to the enhancement in the cell efficiency.Öğe Potassium doping of sputtered MoS2 films by CVD method(Springer, 2024) Altuntepe, Ali; Erkan, Serkan; Olgar, Mehmet Ali; Toplu, Gueldoene; Zan, RecepDoping is an essential approach to enhance the electrical properties of 2D materials. In the present study, two-stage process was used to obtain potassium-doped (K-doped) MoS2. The MoS2 films were grown by magnetron sputtering technique and followed by doping process employing CVD method. The influence of KOH molarity and annealing time on the structural properties of the MoS2 films was investigated thoroughly. 0.2-0.8-M KOH was used to obtain K-doped MoS2. The increase in the molarity of KOH caused a shift in the optical band gap from 1.98 to 1.81 eV. It was observed that increasing the KOH molarity resulted in the loss of homogeneity in the MoS2 films, the use of 0.2-M KOH for the growth of K-doped MoS2 exhibited the most promising results according to performed analyzes. In addition, annealing time also played a critical role in the growth of K-doped MoS2. The dwell times of 5, 10, and 15 min were also used and the effect of molarity and dwell times was investigated. The optical band gap was also shifted from 1.9 to 1.71 eV with increasing the dwell time of KOH. Longer annealing times resulted in the deterioration of the MoS2 film structure. Consequently, an annealing time of 5 min was found to be the optimum value for the growth of K-doped MoS2 film. Overall, this study demonstrates that successful growth of high-quality and homogeneous K-doped MoS2 films which can be employed for various optoelectronic applications.Öğe Substitutional boron doping of graphene using diborane in CVD(Elsevier, 2021) Zan, Recep; Altuntepe, Ali; Erkan, SerkanThis paper reports on a few layer boron doped graphene with high homogeneity, stability and size. To achieve this, we employed diborane to synthesize a boron doped graphene film in a CVD system. During synthesis, we investigated the effect of diborane flow and growth time on copper foil to optimize doped graphene growth conditions. Raman spectroscopy, XPS, EDXS and ellipsometer were employed for the characterization of the doped graphene films. The results of our study enabled the design of a recipe for thin film boron doped graphene growth with optimum optical transmission values. We further found that increasing the flow of diborane from 10 to 30 sccm and growth times from 10 to 30 min leads to the formation of thicker graphene films. However, we discovered that a few layer graphene film with high homogeneity could be obtained for the film that was grown using 10 sccm diborane along with 30-min growth time. The doping was confirmed by observing the shift in the Raman spectra peaks and XPS measurements in comparison to single layer pristine graphene. The study also revealed that boron atoms substituted carbon atoms in the honeycomb structure as confirmed by XPS measurements, which also provide the doping rate to be 2.4%. Our study has significant implications regarding substitutional doping which enables the doping to be stable for a long time, and this is crucial for the doped graphene to be employed in semiconducting technology particularly in optoelectronics.Öğe Synthesis of MoS2 thin films using the two-step approach(2023) Erkan, Serkan; Altuntepe, Ali; Zan, RecepIn this study, MoS2 thin films were grown using two-step approach, which is based on employing both PVD and CVD techniques. The films were obtained initially by sputtering 1nm Mo film in the PVD system and followed by sulphurization of the film in CVD at 700oC. The grown films were optimized employing different sulphurization times. The main difference in our study from the current literature is using preheated CVD furnace (700oC) ahead of sulphurization. The films quality are then investigated using Raman and Photoluminance spectrometer as well as AFM measurements. The Raman spectrums indicate that two characteristic vibration modes of 2H-MoS2 phase were observed in all samples, however, vibration modes of 1T-MoS2 phase were also observed in some films at low sulphurization time. These results were also in line with PL measurements that confirm the direct band transition of the MoS2 films. The surface topography of the films were investigated by AFM for MoS2 films obtained by the sulfurization of 1 nm-thick Mo film in 15 minutes at 700oC which shows MoS2 crystals in triangle shape.
