Silicon solar cell process development, fabricaton, and analysis. Second quarterly report, January thru March, 1979

Solar cells have been constructed from polycrystalline silicon sheet material (10 cm x 10 cm Wacker Silso). These cells have been made using conventional aerospace methods and serve as the so-called baseline cell for analysis and comparison with cells to be made from similar material, but using optimized processing techniques. Before and during the processing of the Wacker baseline cells in a cleaned diffusion tube, control cells were built using the baseline method. All cells were measured on the Spectrolab Mark III Solar Simulator at air mass zero and 28/sup 0/C. Average efficiency for the Wacker Silso baseline cells, using the total device area, was 9.5%. Efficiency was found to vary with location in the sheet. Center regions had higher efficiencies, 9.9% average, whereas corner and edge regions had lower efficiencies, 8.9% average. In general, the efficiency falls off with distance from the center of the sheet. This could possibly be a result of radial grain growth at the edges and grain growth along the axial direction in the core region of the casting. Control cells made from aerospace grade silicon using the baseline process had average efficiency of 11.7%. Like the polycrystalline cells, the control cells had antireflection coatingsmore » of tantalum pentoxide.« less