Crystalline Si solar cells fabricated by CO2 laser doping
We proposed CO<sub>2</sub> laser doping technique as a fabrication method of c-Si solar cell, and demonstrated its availabilities with the cell characteristics. P and B-doping with relatively high carrier density around 10<sup>20</sup> cm<sup>-3</sup> were realized by the CO<sub>2</sub> laser irradiation. We found that the pulse frequency is one of the most important parameter to improve the cell performances.
22.0% Efficient Laser Doped back Contact Solar Cells
Abstract We present the first laser doped interdigitated back contacted solar cells with efficiency η = 22.0%. The cell area is 2 x 2 cm 2 , and contains the metallization of both busbars. The high flexibility and spatial resolution of our laser doping process enables local n-type and p-type doping with a precision below 30 μm and avoids any masking process.
Defect Formation in Silicon During Laser Doping
Laser doping in industrial crystalline solar cells creates a selective emitter and thereby enhances the efficiency. Nevertheless, if not done carefully, the irradiation of the semiconductor introduces defects. We have suppressed defect formation by using a laser beam that is focused to a line with a width of only several micrometers. The maximal line width for a defect free recrystallization, however, depends on the surface orientation of the silicon. Using a transmission electron microscope, we find a dislocation-free recrystallized layer on (100)-oriented silicon wafers that are irradiated with a line focus smaller than or equal to 15 μm. For (111)-oriented surfaces, this holds for the use of a 5.2-μm-wide line focus. Wafers that are irradiated with a circular laser focus of diameter D = 36 μm show the formation of microcracks, but no hints of dislocations are found using transmission electron microscopy (TEM).