We trace the pioneering research and development experiences over the past 25 years which have led to a full scale manufacturing line for photovoltaic modules utilizing polycrystalline silicon wafers produced by the Edge-defined Film-fed Growth (EFG) technique. We examine the progress made in two core areas in detail -crystal growth productivity and wafer bulk quality -which have justified the recent scale up of EFG technology at ASE Americas to the multi-megawatt level. We identify areas in which future advances will enable a crystalline silicon-based EFG technology to compete with cost targets anticipated for the photovoltaics marketplace beyond the year 2000.

List of Figures and Tables Figures Page 2-1 Progression in manufacturing line efficiency increases in 1998 and 1999. 2-2 Histogram of a single lot of >250 cells averaging 14.7%. 2-3 Plot of the increases in electrical yield over the 3 years of the program. 2-4 Contour plots of cell efficiency (%) as a function of the index of refraction, n R , thickness for a silicon nitride antireflection coating. 2-5 Contour plot of Fill Factor vs diffused-layer sheet resistivity and metalization 8 firing temperature 2-6 Improvements in cell fabrication mechanical yield over the three years of PVMaT 5A2. 2-7 Normalized wafer yield from 12/00 to 12/01. 2-8 Line scans of the f-harmonic along wafer diagonal (courtesy of S. Ostapenko, USF) 2-9 Acoustic amplitude at corners for high and low stress EFG wafers) courtesy of S. Ostapenko, USF). 2-10 Stress distribution in two EFG wafers (courtesy of S, Ostapenko, USF). 2-11 Capacitance sensor measurement of position of the surface of a growing experimental octagon tube. 2-12 Fast Fourier Transform (FFT) spectrum of buckle pattern in Fig. 2-11. 2-13 View of Tru-Si Atmospheric Downstream Plasma TM equipment. 2-14 Plasma flame configuration for the ADP TM process. 2-15 Example of submenu options available for statistical data analysis. 17 2-16 Pareto chart showing major contributing factors to Laser Cutting downtime. 2-17 Summary of ISO 9001 certification work. 3-1 Bulk lifetime improvement due to P, Al gettering and SiN hydrogenation. 3-2 50 cm diameter EFG cylinder. 4-1 Main menu from server data base querying user interface. 4-2 Results of a query in the server data base for Flatness Losses vs Tube Number for an experimental growth run of 57 octagon tubes. 4-3 View of module broken due to impact from wind-borne crushed roofing pieces. Arrow shows one of several impact points. 4-4 (a) Disconnected cable in junction box due to poor soldering. (b) Partially wetted solder joint in cable box. 4-5 Layering schematic for lamination structure for new ASE Americas module design. Tables 3-1 Comparison of standard ASE Americas cell process and proposed modifications using RTP methods. 3-2 Cell test parameters for cylindrical EFG multicrystalline Si solar cells. 26

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Sputtered Fe3O4 films have been demonstrated to form rectifying junctions to p-type silicon but ohmic contacts to n-type Si. Ohmic contacts to this Fe3O4 can be provided by Au, Al, or spray-deposited ITO. The redox couple Fe (CN)3−6/Fe(CN)4−6 also appears to make an effective ohmic contact to this iron oxide. The photovoltaic and electrical characteristics of the Fe3O4/p–Si heterojunction are found to depend strongly on the Fe3O4 film thickness.