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Öğe Analysis Of The Electrical Characteristics Of Photodiodes Produced By Dopping Various Metal Oxides(2020) Aslan, Fehmi; Esen, Hikmet; Yakuphanoğlu, FahrettinBu çalışmada farklı metal oksit nano tozlar kullanılarak üretilmiş fotodiyotlar ile ilgili son 10 yılda yapılan çalışmalar kapsamlı olarak ele alındı. Katkılamanın, fotodiyot ve fotodedektörlerin elektriksel özelliklerini ne ölçüde etkilediği araştırıldı. Devre elemanlarının farklı ışık yoğunlukları altında gerçekleştirilen I-V karakteristikleri birbirileri ile mukayese edildi. İnce filmlerin idealite faktörü (n), bariyer yüksekliği (?b), seri direnç (Rs) ve ara yüz durum yoğunluğu (Dit) gibi elektronik parametreleri karşılaştırıldı. Bu parametrelerin fotosensörler üzerindeki etkisi vurgulandı. Ayrıca devre elemanlarının optoelektronik özelliklerinin mevcut literatürle ne derece uyumlu olduğu araştırıldı.Öğe Conjugated diazochalcone-phosphazene hybrids: Design, synthesis, and substituent effects on optical and electrical properties(Elsevier, 2026) Aydin, Derya; Cetiner, Rumeysa; Caliskan, Eray; Aslan, Fehmi; Biryan, Fatih; Koran, KenanPhosphazene derivatives have gained an important place in functional materials chemistry thanks to their versatile structural regularity and chemical stability, while diazochalcone structures are compounds with remarkable potential in organic electronic and photonic applications as photosensitive conjugated systems. In this study, two new hybrid structures, CRG-4F and CRG-4DMA, functionalized with a dual diazochalcone group on the cyclotriphosphazene core, obtained by combining these two important structures, were synthesized, characterized, and their optoelectronic properties were studied in detail. In the optical investigations by UV-Vis spectroscopy, the maximum absorption wavelength of CRG-4F was determined as similar to 350 nm, and that of CRG-4DMA as similar to 405 nm due to the broadening of the conjugation. The direct band gaps calculated by the Tauc method are 2.95 eV and 2.62 eV, respectively, revealing the band gap narrowing effect of the electron-donating dimethylamino group. Both compounds were tested in a diode configuration in Al/organic material/p-Si configuration and exhibited forward conduction and reverse low current characteristics. CRG-4F exhibited superior diode behavior with a higher rectification ratio, while CRG-4DMA stood out as a photosensitive compound by generating more pronounced photoresponse with increasing light intensity under reverse voltage. The results show that the combination of phosphazene core with diazochalcone offers an effective design strategy to develop a new generation of organic-inorganic semiconductors with tunable band gap, solvent-sensitive optical properties, and functional diode performance depending on the nature of the substituent. The findings highlight the potential of these materials in opto-electronic devices, especially in visible region sensitive photodetectors, organic light emitting components, and sensor technologies.Öğe Increasing the photoelectric conversion efficiency of dye-sensitized solar cells by doping SrAl2O4:Eu+2,Dy+3 to TiO2-based photoanodes(Elsevier, 2023) Aslan, FehmiDye-sensitized solar cells (DSSCs) are among the third-generation solar cell technologies that can improve power conversion efficiency by modifying the photoanode. In this study, TiO2 nanoparticles were synthesized by hydrothermal method and SrAl2O4:Eu+2,Dy+3 was doped to this matrix at different rates. XRD results confirmed the formation of anatase TiO2. SEM images reveal aggregation morphology in all samples. TEM images shows that the produced TiO2-based samples are tight rather than scattered. It was understood by BET studies that doped samples had a larger specific surface area than pure TiO2. I-V characterization indicated an increase in efficiency of about 47% with doping.Öğe Investigation of structural, electrical and photoresponse properties of composite based Al/NiO:CdO/p-Si/Al photodiodes(Elsevier, 2022) Gürgenç, Ezgi; Dikici, Aydın; Aslan, FehmiIn the present study, different molar ratios of (1:0, 0:1, 3:1, 1:1, and 1:3) NiO:CdO composite thin films were coated on p-Si by a dynamic sol-gel spin coating method. Structural characterizations of NiO:CdO thin films were performed by XRD, FE-SEM, and EDX analysis. The photoresponse and electrical behavior of the fabricated photodiodes were determined by current-voltage (I–V), transient photocurrent-time (I–t), capacitance-voltage (C–V), conductivity-voltage (G-V), and transient photocapacitance-time (C–t) measurements. All fabricated photodiodes were exhibited rectifying properties and the photocurrent values increased as the light intensity was increased. All photodiodes are sensitive to light and it was determined that the NiO photodiode exhibited the highest photosensitivity value. Photocapacitance and photoconductance values of photodiodes were affected by light. Photoresponse and electrical behavior were affected by the interface states and the NiO:CdO ratio. The results show that Al/NiO:CdO/p-Si/Al photodiodes can be used as photosensors or photocapacitors in optoelectronic applications.Öğe New natural dyes extracted by ultrasonic and soxhlet method: Effect on dye-sensitized solar cell photovoltaic performance(Springer, 2024) Aslan, FehmiThis study employed soxhlet and ultrasonic methods to extract novel natural dyes from Rhamnus tinctoria seed, Rubia fruticosa fruits, and Pinus pinea bark, which were then used as sensitizers in dye-sensitized solar cells (DSSCs). XRD data showed that TiO2 in the photoanode layer was in the anatase phase. The produced DSSCs were assessed for photovoltaic performance and electrochemical charge transfer while sensitizing dyes were characterized using UV-vis spectroscopy and FTIR. Natural dyes leached with different extraction methods showed different absorption behaviors in the UV-vis region. FTIR results revealed the presence of both carbonyl and hydroxyl groups, which enhanced the interaction between the extracted dyes and the TiO2 thin film. All cells using sensitizers obtained by the Soxhlet method showed higher efficiency compared to the ultrasonic method. The highest cell performance (eta = 0.47%) was obtained with 0.71 V V-oc, 0.92 mA/cm(2) J(sc), and 0.72 FF for the sensitizer extracted from Rhamnus tinctoria seeds by the soxhlet method.Öğe TiO2/ZnO-based composite thin films coated on FTO surface by screen printing method: increasing dye-sensitized solar cell performance(Springer, 2024) Demir, Abdullah; Aslan, Fehmi; Esen, HikmetThis study examined the impact of hydrothermally synthesized TiO2:ZnO composite-based nanopowders on the efficiency of dye-sensitized solar cells (DSSCs). Pure TiO2, 3TiO(2):1ZnO, 1TiO(2):1ZnO, 1TiO(2):3ZnO, and pure ZnO thin films were coated on the conductive glass surface by the screen printing method. XRD and SEM were used to examine the thin film's surface photographs and crystal structure, respectively. XRD analyses confirmed the formation of targeted crystal phases in the structure. It was understood from SEM studies that the TiO2:ZnO composite structure was formed successfully. I-V characterization results showed that the cell combined with the composite 3TiO(2):1ZnO electrode had the highest power conversion efficiency (9.9%). In addition, it was determined from EIS analysis that interfacial charge transfer occurred more efficiently in cells with high TiO2 ratio.
