Characterization and optimization of laser edge isolation

Laser edge isolation is a well established industrial process to separate the front emitter from the rear emitter of a silicon solar cell. Since the recombination current at the edge of the laser groove can decrease the conversion efficiency of the solar cell an improvement of the laser edge isolation is desirable. Recently developed laser systems with picosecond pulse widths promise less damage to be induced into the silicon. Especially for the rear side isolation of a Metal-Wrap-Through solar cell an improvement can result in higher efficiencies. McIntosh proposed a two diode model for a solar cell which has a pn-junction that extends to the edge of the cell and showed the influence of the recombination current at the edge on the I-U curve as well as on the efficiency. We used this model to determine the recombination current for two different laser systems and showed that the recombination current is an adequate measurement to evaluate the quality of the laser edge isolation. Furthermore we characterized the isolation groove using ?-photoluminescence measurements to determine lifetimes and mechanical stress near the groove.