Modeling and optimization of PECVD processes and equipment used for manufacturing thin film photovoltaic devices

Özkol, Engin
Plasma enhanced chemical vapor deposition (PECVD) is a common technique used in thin film based device fabrication. Operation conditions of a PECVD reactor need to be optimized in terms of deposition conditions as well as plasma cleaning procedures to deliver desired deposited material qualities. In addition, interactions with external support systems such as gas lines and cabinet, compressors and utility production units need to be understood and characterized. Modeling, whether based on fundamental principles or experimental data, is an essential tool in this optimization process, reducing the time required for experimentation. In this work, a first principles based thermal model of the system is constructed, guiding the design of an improved PECVD chamber delivering better substrate temperature levels and uniformity. On the other hand, material optimization work is supported by the identification of empirical models based on designed experiments, since fundamental models for these interactions are too complicated to be modeled accurately. Individual thin film layers, involved in thin film photovoltaic devices, were optimized in terms of crystallinity, thickness, deposition rate as well as critical optical and electrical properties. The growth of hydrogenated silicon thin films in amorphous (a-Si:H), nano-crystalline, and micro-crystalline regions with intrinsic, nand p- doping types were characterized and optimized. Amorphous silicon nitride (SiNx) thin films with tunable silicon and nitrogen concentration, silver thin films with controlled thickness profile down to nm scale, aluminum doped zinc oxide (AZO) thin films with repeatable uniform conductivity were realized successfully. After completing the optimization of these individual layers, several thin film silicon based photovoltaic devices were fabricated. The different performances that are reported in this work include a p-i-n structured homojunction a-Si:H device, a heterojunction device and a heterojunction with intrinsic thin layer (HIT) structured device. The efficiency values of 2.9 % (initial) for a-Si:H p-i-n structure, 15.9 % for heterojunction solar device and 12.5 % for one sided HIT device were recorded.


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Production of beta-rhombohedral boron carbide (B4C) on a tungsten substrate by the chemical vapor deposition from a BCl3-H-2-CH4 gas mixture was achieved. An impinging-jet reactor was used to minimize the mass-transfer limitations on the reaction kinetics, which made a detailed kinetic investigation possible. Results of the XRD and XPS analyses showed that the solid product formed on the substrate is a rhombohedral B4C phase. Both dichloroborane and boron carbide formation rates were found to increase with ...
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Taburoğlu, Vahit Eren; Özenbaş, Ahmet Macit; Akata Kurç, Burcu; Department of Micro and Nanotechnology (2017)
This thesis analyzes the hydrogenated amorphous diamond like carbon (a-DLC) films coated on aluminum substrates by the technique of plasma enhanced chemical vapor deposition (PECVD). Effects of film thickness, hydrogen content and RF power on the tribology, optical characteristics and structure are observed and studied in detail. DLC films have compressive intrinsic stresses by default. Surface topography revealed by an interferometer shows that too low/high compressive stress is detrimental to the film. In...
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Akdemir, Ozan; Bek, Alpan; İmer, Muhsine Bilge; Department of Micro and Nanotechnology (2018)
Conventional transparent conductive electrodes (TCEs) used in crystal silicon (c-Si) solar cells are commonly made of indium tin oxide (ITO) which provides low sheet resistance and high transparency. However, due to indium scarcity, ITO layers increase the fabrication cost; thus, alternative TCEs, such as fluorine-doped tin oxide (FTO), zinc oxide (ZnO), metal nanowires and Oxide/Metal/Oxide (OMO) multilayers, are being investigated. Conventional solar cells also make use of doped layers, to create the junc...
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The n-type doped silicon thin films were deposited by plasma enhanced chemical vapor deposition (PECVD) technique at high and low H-2 dilutions. High H-2 dilution resulted in n(+) nanocrystalline silicon films (n(+) nc-Si:H) with the lower resistivity (rho similar to 0.7 Omega cm) compared to that of doped amorphous silicon films (similar to 900 0 cm) grown at low H-2 dilution. The change of the lateral rho of n(+) nc-Si:H films was measured by reducing the film thickness via gradual reactive ion etching. T...
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Annealing effect on the structural and optical properties of the quaternary Cu-Ag-In-Se thin film deposited by the thermal evaporation has been investigated. The evaporation source was prepared by using vertical Bridgman-Stockbarger crystal growth system. Structural analysis indicated that annealing the films following to the deposition resulted in the changes from amorphous to polycrystalline phase with the preferred orientation along (1 1 2) direction. In order to determine the optical properties of the t...
Citation Formats
E. Özkol, “Modeling and optimization of PECVD processes and equipment used for manufacturing thin film photovoltaic devices,” Ph.D. - Doctoral Program, Middle East Technical University, 2014.