Laser processing for high-efficiency Si solar cells

High-efficiency silicon solar cells can be fabricated by ion implantation followed by pulsed laser annealing. The proper choice of implantation parameters (energy and dose), laser energy density, substrate temperature, etc., and the improvement of the minority carrier diffusion length of the starting material are important factors in obtaining high efficiency cells. In this paper, we report on experiments which show that substrate heating during pulsed laser annealing can improve the electrical properties of the emitter regions of solar cells. We have also found that the open circuit voltage and the fill factor of ion-implanted, laser-annealed cells can be improved by increasing the emitter dopant concentration, whereas the short circuit current remains fairly constant; these results are in only qualitative agreement with theoretical predictions. By using ion implantation followed by laser annealing to form p-n junctions, laser damage gettering to enhance the minority carrier diffusion length, and laser-induced diffusion for incorporating back surface fields, Si solar cells with efficiencies of over 16% AM1 have been obtained.