Sirvi Autor "Nagpal, Keshav (juhendaja)" järgi
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Kirje Determining the Absorption Wavelengths of Solar Cell Nanomaterials – Case of Zinc Oxide Nanoparticles(Eesti Maaülikool, 2021) Kaeval, Henno; Rauwel, Protima (juhendaja); Rauwel, Erwan Yann (juhendaja); Nagpal, Keshav (juhendaja)In this thesis the absorbance and band gap properties of ZnO nanoparticles (NP), which is a solar cell and photocatalytic material, have been investigated. The absorbance of the ZnO NP were measured using a UV-Vis spectrophotometer and their band gap properties were calculated. Four different samples of ZnO NP were already synthesized. Several steps after synthesis of these NP were carried out before obtaining a powder of ZnO NP, explained in this thesis. To measure the absorbance of these nanomaterials, ZnO NP were spread homogeneously in isopropanol. For absorbance studies, a UV-Vis II Nanocolor spectrophotometer by MACHEREY-NAGEL was used to measure the absorbance with a measurement range of 190–1100 nm. Isopropanol was also used as reference during the measurements. The UV-Vis spectrophotometershows the maximum absorbance of these ZnO NP in 356.8-363.1 nm range. All the results were plotted using software Origin and MS Excel. Energy band gaps were calculated using tauc plot method. The calculated band gap of ZnO NP were in 3.160-3.288 eV range which is comparable with the direct bandgap 3.37 eV of bulk ZnO. These variations in band gap are attributed to the synthesis conditions of these NP.Kirje Photoelectric Properties of ZnO Nanorods(Eesti Maaülikool, 2023) Kaeval, Henno; Nagpal, Keshav (juhendaja); Rauwel, Erwan Yann (juhendaja); Rauwel, Protima (juhendaja)In this study, electrical and photoelectrical properties of ZnO nanorods were investigated. This study is the continuation of my bachelor’s work where I studied absorption and band gap properties of ZnO nanoparticles. The aim of the current study was to investigate electrical properties of ZnO nanostructures. It was found that ZnO nanoparticles studied in my bachelor’s do not show electrical characteristics due to high amount of grain boundaries and non-uniformity. Therefore, the nanorods structure of ZnO was investigated for the electrical measurements. In this study, four samples of ZnO nanorods were investigated, and are classified according to the solvent used for preparing the seeding layer. The nanorods were prepared by a two-step method. The first step includes seeding of zinc precursor. The seeding solution was prepared in four different solvents: ethanol, methanol, isopropanol and 70% ethanol. The second step was the hydrothermal method to grow ZnO nanorods on pre-seeded indium tin oxide (ITO) substrate. The ITO substrate, which consists of 100 nm thick ITO layer deposited on 0.5 mm thick quartz glass substrate were purchased from Ossila [1]. The current-voltage (I-V) characteristics of all four ZnO nanorod samples were studied for two types of contacts: Ohmic and Schottky. The measurements were carried out in two different conditions: in dark and under light exposure, for both type of contacts. A source measure unit (SMU) was used to measure ZnO nanorods conductivity. The measurement range was set to -3 V to +3 V for both Ohmic and Schottky contacts. The data was plotted with Origin Pro software. The Ohmic I-V measurements in dark and room light suggested that methanol seeded ZnO nanorod sample is highly photosensitive to room light itself. The experiments with Schottky behavior were not conclusive for all the nanorod samples. However, sample with isopropanol seeding showed Schottky-like characteristics for the silver (Ag) Schottky contact. The study of Schottky contact needs further investigations and is beyond the scope of this thesis. In conclusion, the enhancement in the current under room light for ohmic contacts for all the nanorod samples suggested that these samples are sensitive to photons emitted by room light. It was expected that room light emits some UV radiation coming from the neon light that excites electrons from ZnO nanorods and resulted in the enhancement of current. As mentioned earlier, the highest enhancement was shown by ZnO nanorods with methanol solution seeding, which suggests that this sample is a good UV light absorber compared to others and is a potential candidate to be used in applications such as solar cells and photo detectors.Kirje Transmittance Properties of ZnO Nanorods Used in Solar Cells(Eesti Maaülikool, 2023) Kelus, Sten; Nagpal, Keshav (juhendaja); Rauwel, Protima (juhendaja)The study of the transmittance and absorbance properties of a material in the design of solar cells is of significant importance. The transmittance of a material determines the ability of light to pass through it. Whereas, the absorbance of a material determines its ability to absorb light. ZnO nanostructures are a good choice for such properties as several studies have shown that ZnO nanostructures show high transmittance (~80%). Also, ZnO nanostructures can absorb most of the UV region of light coming from the sun. In this thesis, the transmittance and absorbance properties of four different types of ZnO nanorod samples were investigated, each of which was prepared with different solvents. The solvents used are ethanol, 70% ethanol, methanol, and isopropanol. A UV-1600PC spectrophotometer was used for measuring the transmittance and absorbance of ZnO nanorod samples. Two types of reference materials were used for the measurements. The results obtained based on the transmittance and absorbance measurements are analysed and compared. Finally, the bandgaps for each of the synthesized nanorods were calculated by using the Tauc relation, and the optimal ZnO nanorod sample for solar cell applications was discussed.