The effect of the curing process on illuminated annealing of silicon heterojunction solar cells

Lamp heating and hot air heating are the two principal methods for metal paste curing used in the manufacture of silicon heterojunction (SHJ) solar cells. Following curing, illuminated annealing (IA) is a process that can improve the electrical performance of SHJ solar cells. In this study, we have investigated the effect of the two curing methods on improving the conversion efficiency (Eff) of illuminated annealing and have explained the effect using calculations based on the double-diode model. The efficiency gain of lamp heating curing decreases when increasing the curing temperature and time and is lower than that achieved by hot air heating curing. Based on the microstructure of the contact interface between gridlines and substrate, as well as the contact resistivity, it is concluded that there is minimal disparity in the paste curing effectiveness between the two methods. Subsequently, a fill factor (FF) loss analysis has revealed that the space charge region recombination after lamp heating is much smaller than that after hot air heating, but is reduced to a similar level following post-illuminated annealing. Pre-metallized samples exhibit enhanced minority carrier lifetime due to curing. The decomposed lifetime curves also confirm that lamp heating decreases the space charge region recombination to a greater extent than hot air heating with a resultant difference in lifetime improvements due to illuminated annealing. Furthermore, a comparison of the measured minority carrier lifetime curves of samples with/without doped silicon films has shown no improvement in samples without doped films following curing and illuminated annealing. This provides further verification that the decrease in space charge region recombination for the carrier is the main cause after curing and illuminated annealing of SHJ solar cells.