Yazar "Sönmezoğlu, Savaş" seçeneğine göre listele

Listeleniyor 1 - 3 / 3
  • Küçük Resim Yok
    Öğe
    Highly efficient tandem photoelectrochemical solar cells using coumarin6 dye-sensitized CuCrO2 delafossite oxide as photocathode
    (PERGAMON-ELSEVIER SCIENCE LTD, 2018) Kaya, İsmail Cihan; Akın, Seçkin; Akyıldız, Hasan; Sönmezoğlu, Savaş
    In this study, we introduce a new concept for the highly efficient tandem p-n photoelectrochemical cell consisting of coumarin6 organic dye-anchored p-type CuCrO2 delafossite semiconductor as photocathodes coupling with traditional n-type TiO2 based photoanodes. Also, we have systematically studied the photovoltaic performance of tandem cells as a function of post-annealing of CuCrO2 films before sensitization. Hydrothermally synthesized CuCrO2 nanocrystals exhibited a high surface area with small crystallite size of 12 nm, phase-pure and well-crystalline after the optimized post-annealing conditions. The experimental results indicated that the optimal post-annealing temperature was 450 degrees C for 1 h due to the larger active surface area, lower R-th and higher J(sc) and V-oc, values. This tandem cell, fabricated by employing the CuCrO2 photocathodes, iodide-based redox mediator and a coumarin6 organic dye, afforded an impressive efficiency of 2.33% with V-oc of 813 mV, J(sc) of 4.83 mA cm(-2), and fill factor of 0.59. The obtained parameters are acceptably high in comparison to NiO photocathode-based tandem cells previously reported in literature under similar experimental conditions. Therefore, this work opened the way for developing highly-efficient tandem photoelectrochemical solar cells.
  • Küçük Resim Yok
    Öğe
    Improvement in electrical performance of half-metallic Fe3O4/GaAs structures using pyrolyzed polymer film as buffer layer
    (TAYLOR & FRANCIS LTD, 2014) Akın, Seçkin; Özel, Faruk; Kuş, Mahmut; Sönmezoğlu, Savaş
    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 k Omega to 85.66 Omega) and extremely low interface state density (1.76 x 10(12) 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.
  • Küçük Resim Yok
    Öğe
    An insight into titania nanopowders modifying with manganese ions: A promising route for highly efficient and stable photoelectrochemical solar cells
    (PERGAMON-ELSEVIER SCIENCE LTD, 2017) Öztürk, Teoman; Gülveren, Berna; Gülen, Mahir; Akman, Erdi; Sönmezoğlu, Savaş
    In this study, we firstly report the synthesis of pure and manganese (Mn) doped titania nanopowders by solution-based chemical process followed by ball-milling and ultra-sonication processes and their usage as photoanode material in dye-sensitized solar cells (DSSCs). Besides examining the properties of physical and charge transfer dynamics, we also made a detailed cost analysis to compare with commercial P25 nanopowders. By incorporating Mn4+ ions into titania matrix, we have also succeeded not only in lower price but also in significantly enhancing the dye loading capability by increasing specific surface area and the retarding the recombination of electron-hole pairs by forming the discrete interstitial states within the band gap as well as accelerating electron transfer by tailoring in energy gap, leading to better photovoltaic performance. Such that, the cell assembled with 0.4 mol% Mn doped TiO2 yields an efficiency of 7.33%, which is similar to 47% and similar to 65% higher than the value obtained for P25 and pure titania-based photoanode, respectively, and shows a fast, stable, and completely reversible photocurrent response accompanying each switch-on/off event. Furthermore, the photoinduced electron transfer (PET) measurements indicate an efficient interfacial charge transfer for 0.4 mol%Mn doped titania (k(ET) = 0.99 x 10(8) s(-1)) compared to the both synthesized pure TiO2 (0.74 x 10(8) s(-1)) and commercial P25 (0.94 x 10(8) s(-1)) photoanodes. This work renders the possibility of synthesizing low-cost and easy-preparation Mn-doped titania nanopowders and describes an innovative approach to further boost the efficiency of green technologies such as solar-driven water splitting, photoelectrochemical and perovskite solar cells applications. (C) 2017 Elsevier Ltd. All rights reserved.