Optimization of metalization in crystalline silicon solar cells

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2012
Demircioğlu, Olgu
Production steps of crystalline silicon solar cells include several physical and chemical processes like etching, doping, annealing, nitride coating, metallization and firing of the metal contacts. Among these processes, the metallization plays a crucial role in the energy conversion performance of the cell. The quality of the metal layers used on the back and the front surface of the cell and the quality of the electrical contact they form with the underlying substrate have a detrimental effect on the amount of the power generated by the cell. All aspects of the metal layer, such as electrical resistivity, contact resistance, thickness, height and width of the finger layers need to be optimized very carefully for a successful solar cell operation. In this thesis, metallization steps within the crystalline silicon solar cell production were studied in the laboratories of Center for Solar Energy Research and Application (GÜNAM). Screen Printing method, which is the most common metallization technique in the industry, was used for the metal layer formation. With the exception of the initial experiments, 6‖ wafers, which are the industry standard today, were used throughout this work. v Typically, screen printing method includes 3 different printing steps on both rear and front surfaces with operating parameters such as squeegee pressure, squeegee speed and snap off. In this study, we have concurrently studied multiple parameters that would affect the metal functionality like aspect ratio, uniformity, thickness, resistance and shadow losses. We also studied the back surface field formation by the aluminum diffusion on the back side of the cell. Subsequent to the printing optimization, drying and firing steps of the metallization were also studied. The improvement in the metallization alone has led to an increase in the efficiency of the cell and a photon conversion efficiency of 15.26 % was obtained. Quality control studies conducted with Ferro GmbH proved the accuracy and the efficiency of the screen printing process carried out at GUNAM. With the improvements in other processes like laser edge isolation, we have reached to an efficiency value of 17 % at GÜNAM Laboratories Recent advances in PV technologies are based on new cell designs such as back contact solar cells, buried contact solar cells, metallization through solar cells and selective emitter solar cells. All these new technologies employ new metallization schemes that enhance the cell performance. These new cell designs and other new innovative approaches will be the subject of our future studies.

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Citation Formats
O. Demircioğlu, “Optimization of metalization in crystalline silicon solar cells,” M.S. - Master of Science, Middle East Technical University, 2012.