Yazar "Polat, Ismail" seçeneğine göre listele

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    Enhanced efficiency of CdS/P3HT hybrid solar cells via interfacial modification
    (Tubitak Scientific & Technological Research Council Turkey, 2019) Yilmaz, Salih; Polat, Ismail; Tomakin, Murat; Unverdi, Ahmet; Bacaksiz, Emin
    The present paper examines the effects of surface modification of CdS with diverse dyes on fabricated CdS-based hybrid solar cells. The X-ray diffraction results showed that CdS thin films had a hexagonal phase with a preferred orientation along the (101) plane. Scanning electron microscopy indicated that the CdS specimen was composed of a granular structure while a P3HT layer was formed from tiny grains. Band gaps of the CdS thin films and the P3HT layer were 2.45 eV and 1.98 eV, respectively. The absorption spectra showed that different dye loading caused an increase in the absorbance of CdS thin films in the wavelength range of 400-650 nm. The photoluminescence of the CdS/P3HT structure including various dyes was lower than that of the pristine one, implying that efficient charge separation was achieved upon surface modification. Current density-voltage curves showed that the ITO/CdS/N719/Ag hybrid solar cell exhibited the best overall efficiency of 0.082%, which can be attributed to improvements in both short circuit current density (J(sc)) and open circuit voltage (V-oc). These enhancements can be attributed to the creation of better interfacial contact between CdS and P3HT layers after dye loading.
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    Enhancement of the response speed of CIGS-based photodetector by Te-doping
    (Elsevier Science Sa, 2024) Yilmaz, Salih; Basol, Bulent M.; Atasoy, Yavuz; Polat, Ismail; Kucukomeroglu, Tayfur; Bacaksiz, Emin
    Cu(In,Ga)Se2 (CIGS) based devices are promising candidates for high performance photodetector applications. The present work investigated the effects of Te-doping on the properties of CIGS layers and studied the performance of photodetectors (PDs) fabricated on these films. The films were vacuum evaporated on glass substrates and their morphological, structural and optical properties were evaluated after an annealing step at 550 degrees C. Morphological data indicated that undoped CIGS films had non-uniform surface features with large grains separated by nanoparticles. Addition of 6.6 % Te improved the morphology and yielded a smoother layer. Further increase in Te concentration showed appreciable reduction in surface feature size and shape. X-ray diffraction patterns showed that increasing the Te amount in CIGS caused a shift in the XRD peaks towards smaller angles pointing to replacement of Se atoms by Te. Peak splitting at higher Te samples suggested a graded structure with Se and Te amounts changing through the thickness of the film. Raman analysis demonstrated formation of CuInGa(Se,Te)2 (CIGST) compound. According to Tauc's approximation, CIGS films with and without Te atoms possessed two energy band gaps of Eg1 and Eg2 that were in the ranges of 1.10-1.28 eV and 1.16-1.36 eV, respectively. Electrical data obtained from photodetector devices showed a responsivity of 4.44x10- 1 A/W and a detectivity of 8.01x107 Jones for Te-free material, while the rise/fall times were measured as 34/148 ms. A much faster response speed of 19/20 ms was reached for devices fabricated on films with 10.2 % Te. This work demonstrated, for the first time, the fabrication low-cost and high-performance metalsemiconductor-metal (MSM) type CIGST-based PDs.
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    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, Emin
    The 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.
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    Investigation of growth temperature effects on SnSe-based photodetector performance
    (Springer, 2023) Yilmaz, Salih; Basol, Bulent M.; Polat, Ismail; Ciris, Ali; Kucukomeroglu, Tayfur; Bacaksiz, Emin
    SnSe thin films were synthesized by thermal evaporation on glass slides at elevated growth temperatures. The grown films were investigated in terms of structural, morphological and optical properties. Furthermore, electrical characteristics and time-dependent photoresponses of SnSe-based photodetectors were studied in depth. SnSe thin films showed orthorhombic crystal structure with a preferred orientation of (400) for the growth temperature of 150 & DEG;C. However, the preferential orientation changed from (400) to (111) with increasing of growth temperature to 200 & DEG;C. Top view SEM data displayed a porous morphology for the samples grown at 200 & DEG;C and 250 & DEG;C temperatures. More transparent SnSe films were obtained when the growth temperature was increased to 200 & DEG;C. The band gaps of SnSe sample deposited at 150 & DEG;C and 200 & DEG;C were determined to be 1.22 eV. However, band gap reduces to 1.06 eV with the increase of the substrate temperature to 250 & DEG;C. Raman data demonstrated the shift in the general peak positions to higher frequencies as the growth temperature is increased due to the variation in bond lengths between Sn and Se atoms. Photocurrent-time data showed that SnSe sample grown at a growth temperature of 200 & DEG;C possessed the highest photocurrents because of the formation of porous structure. Rise and fall times of SnSe-based photodetector decay systematically with increasing growth temperature and the maximum responsivity and detectivity were found to be 3.33 x 10-1 A/W and 2.03 x 107 Jones, respectively for the device employing the film deposited at 200 & DEG;C.
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    Role of Mg doping in the structural, optical, and electrical characteristics of ZnO-based DSSCs
    (Tubitak Scientific & Technological Research Council Turkey, 2017) Polat, Ismail; Yilmaz, Salih; Tomakin, Murat; Bacaksiz, Emin
    ZnO- and Mg-doped ZnO samples are prepared by spray pyrolysis on conducting glass substrates to fabricate ZnO-based dye-sensitized solar cells (DSSCs). Influences of Mg-doping content on the power conversion efficiencies of ZnO-based DSSCs are investigated. X-ray diffraction results show that all the samples exhibit a hexagonal wurtzite structure. Scanning electron microscopy data indicate that the ZnO sample has uniform rods with 1 mu m diameter. With respect to ZnO, the band gap value of 4 at.% Mg-doped ZnO samples improves to the value of 3.27 eV and a further increase in Mg level up to 6 at.% gives rise to a decline in the band gap value of 3.22 eV. Photoltuminescence measurements illustrate that intensities of the ultraviolet peak and a red luminescence peak take their maximum values for 4 at.% Mg doping. From solar cell performance measurements, the best power conversion efficiency of 0.08% is obtained for the doping amount of 4 at.% Mg.
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    The influence of Cu-doping on structural, optical and photocatalytic properties of ZnO nanorods
    (Elsevier Science Sa, 2014) Polat, Ismail; Yilmaz, Salih; Altin, Ilknur; Bacaksiz, Emin; Sokmen, Munevver
    Undoped and Cu-doped ZnO nanorods with different copper contents were produced on glass substrates. The structural and optical properties of the samples were investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) measurements. Irrespective of the Cu content in ZnO nanorods, X-ray diffraction results showed that all the ZnO nanorods had a hexagonal structure with a strong preferred orientation along (002) direction. SEM results indicated that increasing Cu content caused a change from the pyramidal geometry to a hexagonal rod shape in the morphology of ZnO. Photoluminescence measurements exhibited two emission bands in the spectra: one sharp ultraviolet luminescence at similar to 379 nm and one broad visible emission ranging from 400 to 720 nm. The photocatalytic properties of undoped and Cu-doped ZnO nanorods synthesized by a chemical bath deposition method were studied for the first time in this study by using photocatalytic degradation of methylene blue (MB, 9.4 x 10(-6) M) as a model chemical. (C)2014 Elsevier B.V. All rights reserved.