Laser Transfer of Metal Contacts and Dopants for Silicon Solar Cells

Crystalline silicon has been the primary raw material in the industrial manufacturing of solar cells. Silicon Photovoltaics (PV) technologies have been advancing rapidly towards higher efficiency, cost reduction and simplification of fabrication processes. Traditional processes, including emitter and metal contacts formation, have been largely relying on high-temperature process. In this dissertation, we explored alternative processes using a laser-based approach for reduction of cost due to low temperature processing.
A pulsed ytterbium fiber laser has been used for metal contacts formation and doping process for silicon solar cell fabrication using laser transfer. Both front and rear metallization were achieved through laser induced forward transferring. The crystalline silicon solar cell based on all-laser-transferred contacts (ALTC) was fabricated on chemically textured p-type Cz silicon wafers with a simple cell structure of full-area emitter. An initial conversion efficiency of over 15% was achieved. To demonstrate the laser transfer of dopants, a phosphorous dopant was laser transferred through the dielectric passivation and antireflection layer followed by metallization using electroplating. The resultant silicon solar cell has line-shaped junctions formed by laser transferring process and showed current density as high as 34.5 mA/cm2 without any surface texturing. Both optical and electrical characterizations were carried out to study the laser transfer of metal contacts and dopants. Simulations were performed using PC1D and PC2D to better understand the limitations and future improvements. The ALTC and laser transfer of dopants demonstrate the advantage of laser processing in simplifying the solar cell fabrication process also replaces the high-temperature furnace with room-temperature process.