Rapid Thermal Annealing of Screen-printable Atmospheric Cu Pastes for PERC Solar Cell

This paper reports on the investigation of the rapid thermal annealing of screen-printable Cu paste for cost-effective metallization of PERC cells. The preliminary results of screen-printable contacted solar cells show that the challenges of Cu including rapid diffusion into Si at high temperature and oxidation in the atmospheric ambient are overcome. The open circuit voltage (VOC) of 662 mV, shunt resistance of 25000 Ω-cm2, the reverse saturation current density (JO2) of 4.4E-9 A/m2 attest to this fact. The VOC was found to increase as the belt speed was varied from 300–350 inches per minute (IPM). The peak temperature varied somewhat for the belt speed with highest peak temperature of 590°C at 300 IPM and 584°C for the 350 IPM. The efficiency peaked at the 300IPM belt speed, which showed the lowest series resistance and highest fill factor (FF). However, the electroluminescence micrographs show similar brightness between the cells sintered with belt speeds of 300 IPM and 350 IPM. The result supports the observation that Cu pastes favors fast belt speeds, which enables uniform formation of local back surface field (BSF). Finally, this result shows a viable future for atmospheric Cu paste to replace the expensive Ag metal.