Rapid Thermal Processing of Cost-Effective Contacts for Silicon Solar Cells

This paper reports on the investigation of rapid thermal processing (RTP) of contacting the Al-BSF solar cell with Ag, Cu, and Ni in conjunction with aerosol printing technique. The study showed a liftoff and delamination, respectively, for the bi and tri stack layers of Ag frit/Ni and Ag frit/Ni/Cu fired above 790°C peak firing temperature. The 770°C peak firing temperature gave excellent electrical performance for both bi and tri stack layer contacts, which is not favorable to forming thick back surface field (BSF) required for high open circuit voltage (V _OC ). This suggests that the bilayer and trilayer contacts involving Ag frit are limited to low peak firing temperature, but Ni frit, on the other hand, showed a wider firing temperature range. This is supported by low reverse saturation current density (J ₀₂ ) of 1.1 × 10 ⁻¹¹  A/cm ² and high shunt resistance (R _SH ) of 5750 Ω·cm ² for the Ni frit fired at 800°C peak firing temperature. More so, the adhesion of Ni Frit to silicon is better than Ag counterpart as evidenced in the SEM micrograph. Thus, by adopting RTP Ni/Cu contacts, the cost of metallization of solar cell can be dropped from 35% of total processing cost to only 5% to 6%, which is approximately 30% drop in the total cost of processing.