Effects of Laser Doping on the Formation of the Selective Emitter of a c-Si Solar Cell

Laser doping, though able to improve cell characteristics, enables the formation of a selective emitter without the need for additional processing. Its parameters should be investigated to minimize laser defects, such as the heat-affected zone (HAZ), and to obtain a low contact resistance. Herein, the laser fluence and speed were changed to optimize process conditions. Under a laser fluence of 1.77 J/cm2 or more, the surface deteriorated due to the formation of the HAZ during the formation of the laser doping selective emitter (LDSE). The HAZ prevented the formation of the LDSE and impaired cell characteristics. Therefore, the laser speeds were changed from 10 to 70 mm/s. The lowest contact resistivity of 1.8 mΩ·cm2 was obtained under a laser fluence and speed of 1.29 J/cm2 and 10 mm/s, respectively. However, the surface had an irregular structure due to the melting phenomenon, and many by-products were formed. This may have degraded the efficiency due to the increased contact reflectivity. Thus, we obtained the lowest contact resistivity of 3.42 mΩ·cm2, and the damage was minimized under the laser fluence and speed of 1.29 J/cm2 and 40 mm/s, respectively.