Laser-Doping Technique Using Ultraviolet Laser for Shallow Doping in Crystalline Silicon Solar Cell Fabrication

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The laser-doping technique in silicon solar cell fabrication is now attracting considerable attention because of its suitability for the low-cost processing of high-efficiency silicon solar cells; it can be performed at room temperature in air and intricate doping areas can be formed easily. In this study, we used a laser with a UV wavelength (355 nm) instead of the conventionally used laser with 532 nm wavelength to form property-controlled doping regions for the emitter or back surface field (BSF) of silicon solar cells at room temperature in air. The doping depth of phosphorus or boron was precisely controlled in the shallow region under 0.3 μm depth by changing the laser output power, remaining a high doping concentration at the silicon surface. The photovoltaic performance depended strongly on the doping conditions, and the best cell with a laser-doped emitter showed almost the same open circuit voltage and short circuit current as those of a cell fabricated by the conventional thermal diffusion method. In addition, all photovoltaic properties were enhanced by the formation of a laser-doped BSF layer. The problem of a lower fill factor still remained because of the high sheet resistance caused by laser damage, inhomogeneous doping, or the unintentional incorporation of oxygen and/or carbon atoms. However, the utility of the laser-doping technique was clearly shown; silicon solar cells were fabricated below 100 °C.
2009-07-25