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  • Küçük Resim Yok
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    Effect of reduced graphene oxide addition on cathode functional layer performance in solid oxide fuel cells
    (Pergamon-Elsevier Science Ltd, 2023) Timurkutluk, Cigdem; Zan, Recep; Timurkutluk, Bora; Toruntay, Furkan; Onbilgin, Sezer; Hasret, Onur; Altuntepe, Ali
    Solid oxide fuel cells (SOFCs) operating at high temperatures are highly efficient electrochemical devices since they convert the chemical energy of a fuel directly into heat and electrical energy. The electrochemical performance of an SOFC is significantly influenced by the materials and microstructure of the electrodes since the electrochemical reactions in SOFCs take place at three/triple phase boundaries (TPBs) within the electrodes. In this study, graphene in the form of reduced graphene oxide (rGO) is added to cathode functional layer (CFL) to improve the cell performance by utilizing the high electrical properties of graphene. Various cells are prepared by varying the rGO content in CFL slurry (1-5 wt %), the number of screen printing (1-3) and the cathode sintering temperature (900-1100 degrees C). The electrochemical behavior of the cells is evaluated by electrochemical performance and impedance tests. It is observed that there is a similar to 26% increase in the peak performance of the cell coated with single layer CFL having 1 wt % graphene and 1050 degrees C sintering temperature, compared to that of the reference cell. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    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, Murat
    This 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.
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    Katkılı grafen ve grafen oksit kaplanan alüminyum yüzeylerin mekanik davranışları
    (Niğde Ömer Halisdemir Üniversitesi, 2024) Hasret, Onur; Zan, Recep
    Tez kapsamında alüminyum plakalara GO ve rGO kaplanarak dayanımları iyileştirilmiştir. Tüm deney grupları için ilk olarak Raman spektroskopisi kullanılarak karakterizasyon gerçekleştirilmiştir. Raman spektroskopisi ile yapılan karakterizasyon işleminden sonra, katkılamanın gerçekleştiğine dair yorum yapılan numuneler için XPS analizleri uygulanmıştır. Elde edilen Raman spektroskopisi sonuçlarına göre, GO, N GO, rGO ve N-rGO'nun pik pozisyonlarının literatürle uyumlu olduğu tespit edilmiştir. Ayrıca, alınan XPS ölçümleri sonucunda, GO ve rGO'ya yapılan katkılamaların kalıcı ve homojen bir şekilde gerçekleştiği, N-GO ve N-rGO'ya yapılan N-katkısının sırasıyla %2 ve %2.5 oranında olduğu belirlenmiştir. Katkılı ve katkısız GO ve rGO'nun Al-1050 plakalar üzerine çözelti haline getirilerek kaplanmasıyla dayanım üzerindeki etkileri incelenmiştir. Al-1050 plakasının çekme dayanımı, 67 dakika sonunda 107 MPa olarak ölçülmüştür. Al-1050 plakaları üzerine GO, N-GO, rGO ve N-rGO kaplanmış ve çekme dayanımları sırasıyla 120 MPa, 127 MPa, 122 MPa ve 119 MPa olarak ölçülmüştür. Bu ölçümlerin dayanım süreleri sırasıyla 75 dakika, 80 dakika, 76 dakika ve 74 dakika sürmüştür. Bu sonuçlar ışığında, en yüksek çekme dayanımına (127 MPa) ve dayanım süresine (80 dakika) sahip olan numunenin N-GO olduğu belirlenmiştir. Anahtar Sözcükler: Grafen, GO, rGO, katkılı grafen, Al plakalar
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    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 Ali
    Aluminum-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.