Optical and electrical characterization of high-dose ion implanted, laser-annealed silicon solar cells

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Abstract
N +/p and p+/n/n+ solar cells were fabricated by using ion implantation and pulsed laser annealing. With these techniques it is possible to obtain emitters which are doped well beyond the solubility limit and present lower sheet resistivities for equal junction depth. The dopants used were phosphorus, arsenic, and boron, and the implanted doses ranged from 2×1015 at/cm2 up to 5×1016 at/cm2. Measurements of diffusion length, quantum efficiency, and reflectivity enabled us to demonstrate that the supersaturated layers are characterized by high values of the absorption coefficient, which determines a poor short-circuit current and consequently a low conversion efficiency. This effect seems to be very marked for concentrations higher than 1021 at/cm3. Also, the reflectivity depends on the surface doping, showing a considerable decrease for the highest concentrations examined.