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    Fabrication of Cu-rich CZTS thin films by two-stage process: Effect of gas flow-rate in sulfurization process
    (Elsevier, 2021) Olgar, M. A.; Altuntepe, A.; Erkan, S.; Zan, R.
    In this study, CZTS thin films were prepared using a two-stage process consisting of sputter deposition of Cu, Sn and ZnS layers on the glass substrates to form CuSn/ZnS/Cu stacked precursor films followed by sulfurization process under various flow-rate (0, 20, 40, 60, 80, 100 sccm) of Ar+ H-2 mix gas in a tubular furnace. The EDX measurements of the precursor and reacted films are Cu-rich and Zn-rich composition. However, Zn and Sn loss was observed for samples annealed under the flow-rate of gas above the 60 sccm. The XRD pattern of the samples showed diffraction peaks of pure kesterite CZTS structure and the FWHM values extracted from their XRD patterns and W-H plot calculations demonstrated that CZTS-40 thin film had a more desired crystallite size. The Raman spectra of the samples confirmed the formation of CZTS phase for all samples and indicated the formation of some secondary phases such as Cu2SnS3, SnS2, Sn2S3 except for CZTS-40 thin film. All the samples displayed dense and polycrystalline microstructure according to their SEM images. The optical band gap values of CZTS samples showed variation between 1.40 and 1.48 eV. The room-temperature PL spectra of the samples revealed a broad band that had a peak value at around 1.36-1.40 eV that are close to the optical band gap values for prepared CZTS samples. (C) 2021 Elsevier B.V. All rights reserved.
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    Integration of single layer graphene into CZTS thin film solar cells
    (Elsevier Science Sa, 2022) Erkan, S.; Yagmyrov, A.; Altuntepe, A.; Zan, R.; Olgar, M. A.
    In this study, CZTS samples were produced on Mo and graphene/Mo coated glass substrates using qua-ternary target. The CZTS thin films deposited by RF magnetron sputtering were annealed using rapid thermal processing (RTP) method in sulphur atmosphere at 500, 525, and 550 degrees C so as to obtain glass/Mo/ CZTS and glass/Mo/graphene/CZTS (g-CZTS) structures. The obtained CZTS and g-CZTS thin films were then characterized by several methods such as EDX, XRD, Raman spectroscopy, SEM etc. The EDX data demon-strated that all CZTS thin films had Cu poor composition regardless of the sulfurization temperature and increasing the temperature led to Sn loss from the films. Diffraction peaks of kesterite CZTS phase were observed in all the samples; additionally, SnS and CuS secondary phases were also observed in CZTS samples annealed at 500 degrees C. The crystallite size of the CZTS thin films were found to be increasing with both increasing annealing temperature and use of graphene film as an inter-layer. The creation of kesterite phase with a very small CTS phase in all the samples were verified by the Raman spectroscopy measurement. The SEM images of the samples indicated that using graphene improves the crystalline quality of the CZTS films and contributes to forming more compact, homogenous and larger crystal structure. The determined optical band gap values varied from 1.41 to 1.44 eV depending on the Sn-content of the samples. The produced solar cells selected from the more promising absorber layers showed that implementing graphene in CZTS cell structure enhanced the conversion efficiency from 2.40% to 3.52% due to improvement of crystalline quality of the absorber layer. (c) 2022 Elsevier B.V. All rights reserved.
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    Permanent Boron Doped Graphene with high Homogeneity using Phenylboronic Acid
    (Elsevier, 2021) Altuntepe, A.; Zan, R.
    In this paper, we report on boron doped graphene synthesis using phenylboronic acid as a single source of carbon and boron. The growth conditions were established and optimized to improve the opto-electronic properties of a graphene film. The effects of the phenylboronic acid amount and growth time on the synthesis of graphene were investigated under similar growth conditions on polycrystalline copper foil in a three-zone CVD system. Based on Raman and XPS analysis, boron doped graphene was successfully synthesized under the given growth conditions in this study. It was also found that increasing the amount and growth times led to thicker graphene films. However, a single layer region was only found for a film grown using 0.5 gr phenylboronic acid along with 30-minute growth time, which is in contrast with the current literature. Additionally, carbon atoms were found to be substituted by the boron atoms in the honeycomb structure as revealed by the XPS measurements. Substitutional doping enables the doping to be stable for a long time, which is crucial for the doping to be employed in semiconducting technology particularly in optoelectronics. (C) 2020 Elsevier B.V. Allrightsreserved.