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

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2014
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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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.