High Efficiency Silicon Solar Cells
Power conversion efficiencies above 20% have been measured for silicon solar cells in concentrated sunlight. The cells are p+ -n-n+, 0.3 Ω-cm base, single crystal silicon. Two cell sizes, roughly 1 and 4 cm2, were tested. The larger cell exhibited a 17.7% efficiency at one sun and exceeded 20% from about 20 to 50 suns. The smaller cells were above 20% in the range 50 to 100 suns. All measurements were at 27 C. The difference between the two types of cells can be accounted for by shadowing and series resistance of the metal pattern. The one-sun data agree with values predicted by theoretical analysis of the cell.