3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Simulation of highly efficient solar cells(2018) Aslan, TahirIn this thesis, we will consider problems causing losses in solar cells and try to solve these problems using numerical methods. We will simulate metal nanoparticles (MNPs) are embedded in order to enhance light absorption for thin film solar cells, which otherwise have insufficient absorption of light. To avoid thermal and sub-band losses, we will pick up the idea of using energy conversion processes in single junction solar cells, and discuss modeling of generic up-conversion (UC) and down-conversion (DC) processes, based on rare-earth ions in the context of solar cell device simulations. These numerical simulations are supposed to accompany future experimental studies and practical implementation of such processes in various types of inorganic solar cells. To understand and get parameters that we will need to determine extra current from frequency conversion, the Judd-Ofelt theory [1] has been used. This work is organised as follows: After describing the basic working principles of a solar cell, we will give an introduction to modern solar cell device simulations, where we discuss the basic equations and simulation parameters [2] and show that most of the key parameters may be taken from ab initio numericaldata,ratherthanexperimentaldata. Wewillpresentvariousnumerical approaches, photon absorption/emission processes and a more advanced approach using rate equations [3, 4]. Finally we discuss a simple strategy to implement UC and DC layers into solar cell device simulations. Note that this thesis is among the first systematic studies of implementing augmenting features into solid state device simulation, apart from crude estimates based on detailed balance models.Item Electronic transport properties of silicon nanowires synthesized by laser ablation(2015) Aslan, TahirIn this thesis electron transport properties of silicon nanowires are studied. The devices are synthesized using a laser ablation technique. The catalysts used in the synthesis are nickel nanoparticles. The silicon nanowires are characterized by scanning electron microscopy, transmission electron microscopy, atomic force microscopy and Raman spectroscopy. Dielectrophoresis is used to align and contact nanowires across two electrodes to create two-terminal devices. In addition four-terminal devices are fabricated using PMMA lift-off based electron beam lithography. Electron transport properties of the fabricated devices have been studied using dc measurement techniques. Resistance of the silicon nanowires has been measured as a function of temperature and magnetic field. These measurements have been accomplished using a Cryogenics system at low temperature, and high magnetic field. Temperature dependent studies reveal that Arrhenius type thermally activated transport behavior is the dominant transport mechanism in measurements at zero magnetic field. Magnetic field dependent measurements show a weak positive linear magnetoresistance. There are also strong oscillations in magnetoresistance curves. The temperature and field independence of the oscillations has been attributed to quantum interference effects.