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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 Grafen Tabanlı Hibrit Saydam Elektrot Dizaynı Ve Günes Hücresi Uygulamaları(2020) Zan, Recep; Olgar, Mehmet Ali; Sürmegözlüer, Ayşe SeyhanIsıgı geçiren ve elektriksel olarak iletken olan saydam iletken elektrotlar (TCE), dokunmatik ve esnek ekran teknolojilerinde (LCD, OLED) ve fotovoltaik hücreler gibi birçok optoelektronik aygıtlarda kullanılan temel bilesenlerden bir tanesidir. Dogada bilinen rezervleri sınırlı olan indiyumun yogun olarak kullanıldıgı saydam iletken elektrotlar yüksek maliyet ve mekanik olarak düsük dayanım gibi dezavantajlara sahiptir. Bu özellikler tüm dünyada indiyum içermeyen saydam iletken elektrotların gelistirilmesi arayısını tüm dünyada hızlandırmıstır. Bu amaç dogrultusunda, projede çinko oksit (ZnO), alüminyum katkılı çinko oksit (AZO), molibden katkılı çinko oksit (MZO), galyum katkılı çinko oksit (GZO) ve indiyum kalay oksit (ITO) saçtırma teknigi kullanılarak farklı kalınlıklarda üretilmis ve yapısal, elektriksel ve optik özellikleri incelenmistir. Daha sonra bu yapılara tek tabakalı grafen transfer edilerek hibrit elektrot yapısı olusturulmus ve en iyi performans (yapısal, elektriksel ve optik) gösteren hibrit elektrot yapısı belirlenmistir. Projenin devamında silisyum tabanlı PN yapısı olusturulmus ve TCE olarak optimize edilen hibrit yapılar kullanılarak hetero-eklem günes hücrelerinin üretimi tamamlanmıstır. Bu kapsamda grafenli ve grafensiz bütün TCE yapılar kullanılarak hücreler üretilmis ve son asamada ise hücre verimlilikleri belirlenmistir. Tek tabakalı formdaki grafen kullanımı ile üretilen hibrit TCE yapıların kullanıldıgı hücrelerin verimliliginin grafen kullanılmadan üretilen hücrelerden daha yüksek oldugu tespit edilmistir. Bununla birlikte verimlilik artısının oransal olarak en yüksek oldugu hücrenin GZO+grafen yapısının kullanıldıgı hücre olmustur. Proje ile alternatif elektrotların gelistirilmesi, günes hücresi üretiminde daha az malzeme kullanımı ve/veya aynı miktarda malzeme kullanımı ile daha verimli hücre üretiminin mümkün olabilecegi gösterilmistir.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 Improved CZTSe solar cell efficiency via silver and germanium alloying(Pergamon-Elsevier Science Ltd, 2024) Atasoy, Yavuz; Bacaksiz, Emin; Ciris, Ali; Olgar, Mehmet Ali; Zan, Recep; Ali, Ahmed M. J. Al-dala; Kucukomeroglu, TayfurIn this study, we report systematic investigation of the effects of Ag and Ge alloying on properties of CZTSe layers, as well as, on the performance of solar cells fabricated using these films. In this context, Ag-Ge doped CZTSe layers were produced by selenization of Cu/Sn/Zn/Cu/(Ag,Ge)/Se precursor stack structures using rapid thermal processing. All precursor stacks and the Ag-Ge doped CZTSe films obtained after selenization exhibited (Cu + Ag)-poor and Zn-rich chemical composition. XRD studies demonstrated pure kesterite phase for all reacted films. Raman spectra confirmed this finding. Cross-sectional SEMs showed large grain structure, which resulted from Ag-Se and Ge-Se liquid phase formation that assisted crystal growth during high temperature annealing. While a slight Ag-front-gradient was achieved in Ag-doped CZTSe film, the Ag gradient disappeared with incorporation of Ge into the lattice. Addition of Ge formed a gradient within the material such that near-contact region was more Ge-rich. Solar cells fabricated using films with various compositions demonstrated that double doping CZTSe with both Ag and Ge improved the device efficiency from about 5 % to over 8 %.Öğe Improvement in performance of SnSe-based photodetectors via post deposition sulfur diffusion(Elsevier Science Sa, 2024) Yilmaz, Salih; Basol, Bulent M.; Polat, Ismail; Olgar, Mehmet Ali; Bayazit, Tugba; Kucukomeroglu, Tayfur; Bacaksiz, EminThe work represents an enhancement in the photodetector properties of thermally evaporated SnSe thin films through both annealing and sulfurization processes. X-ray diffraction analysis showed the formation of SnSe 1-x S x alloy with a graded composition that was more S -rich near the surface when the sulfurization process was applied at 350 degrees C. Scanning electron microscopy results indicated that increasing the annealing temperature from 300 degrees C to 350 degrees C changed the microstructure greatly. When the sulfurization temperature was increased from 300 degrees C to 350 degrees C, the direct band gap of SnSe thin films decreased from 1.38 eV to 1.30 eV while the indirect band gap reduced from 0.91 eV to 0.71 eV. Raman spectra also confirmed the development of phase of SnSe 1-x S x for the sulfurized sample at 350 degrees C. Photocurrent-time curves of devices fabricated on all films demonstrated that sulfurization at high temperature increased the photocurrent values. It was further determined that devices made on sulfurized layers had smaller rise/fall times of 2.57/2.33 s compared to those fabricated on non-sulfurized films. The best responsivity and detectivity values were achieved as 2.07 x 10 -1 A/W and 1.19 x 10 7 Jones, respectively, for photodetectors fabricated on layers sulfurized at 350 degrees C.Öğe Influence of deposition pressure of elemental Sn on structural, optical, electrical and schottky diode properties of SnS thin films grown by two-stage method(Springer, 2023) Ciris, Ali; Atasoy, Yavuz; Tomakin, Murat; Olgar, Mehmet AliIn the present study, SnS thin films were grown by two-stage method including sputtering deposition of elemental Sn films at various deposition pressures (6, 9, 12 ,15 and 18 mTorr) followed by sulfurization process carried out by Rapid Thermal Processing method at 350 degrees C for 1 min. The fabricated SnS thin films were characterized by several techniques. The energy dispersive X-ray spectroscopy measurements showed that deviation from stoichiometry in chemical composition of SnS samples deposited at above 9 mTorr was observed. X-ray diffraction and Raman spectroscopy measurements confirmed formation of orthorhombic SnS phase and SnS2 secondary phase. Furthermore, both characterization method also revealed that the preferential orientation of orthorhombic SnS phase altered from (111) to (040) by increasing the deposition pressure at above 9 mTorr. Scanning electron microscope images displayed formation of polycrystalline surface morphology. While lower deposition pressure (6 mTorr) gave rise to form small grains, the high deposition pressure (above 12 mTorr) caused some agglomerations. Optical bandgap of the films varied between 1.02 eV and 1.08 eV by varying the deposition pressure. SnS samples prepared at 9 and 12 mTorr deposition pressures presented lower resistivity and higher carrier concentration values. Due to more promising results of SnS samples fabricated utilizing 9 and 12 mTorr deposition pressures regarding structural and electrical properties, Schottky diode properties of both samples were investigated. The current-voltage characteristic of Mo/SnS/Al diode structure showed that SnS samples prepared at 12 mTorr has more ideal diode characteristic, comparatively.Öğe Integration of graphene with GZO as TCO layer and its impact on solar cell performance(Pergamon-Elsevier Science Ltd, 2022) Zan, Recep; Olgar, Mehmet Ali; Altuntepe, Ali; Seyhan, Ayse; Turan, RasitIn this study, we investigated the impact of incorporating graphene with Ga-doped ZnO (GZO) when employing them as a TCO layer on Si-based solar cell. GZO thin films with various thicknesses (50-450 nm) were fabricated by the sputtering method using a single target. The aim here was to determine the GZO film with the optimum thickness to incorporate it with single layer graphene as TCO. This thickness was found to be 350 nm as that was the best crystalline quality found in the Opattern. Further, this sample had the lowest sheet resistance and highest transmission values as confirmed by electrical (sheet resistance), and optical characterizations (transmission). Topographic (SEM and AFM), electrical (resistivity and carrier concentration) measurements were also conducted on the same sample. The graphene film grown on copper in a CVD system was then transferred on top of this sample to fabricate the hybrid TCO structure. We found that graphene integrated GZO hybrid TCO film showed higher sheet resistance due to high sheet resistance of graphene and similar optical properties thanks to high optical transmission of graphene. Employing graphene-based TCO layer in the solar cell resulted in higher open-circuit voltage, consequently improving the conversion efficiency from 10.0% to 11.2%. (c) 2021 Elsevier Ltd. All rights reserved.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 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.
