Progress in production-worthy point contact solar cells process

This work reports on the integration process of rear point contact solar cells with reduced recombination and better light trapping than the conventional cells. Al₂O₃/SiN_x passivation stacks were used to ensure the backside passivation and the effective lifetime of minority carrier is found to be >;100 μs (estimated surface recombination velocity ~50 cm/s) on solar p-type Cz wafers. The estimated fixed charge associated with the Al₂O₃ is in the range of -5e12 C/cm². Laser ablation of Al₂O₃/SiN_x stack and aluminum alloying are studied in detail to understand the process window for clean ablation and back surface field. It is found that laser energy plays an important role cleanly ablating the Al₂O₃/SiN_x passivation stack. The solar cell is fabricated using standard processes based on screen-printed aluminum paste onto laser ablated passivation layer consisting of Al₂O₃/SiN_x. Aluminum alloying is dependent on the firing profile and amount of Al melted into Si. Back point contact cells show improvements in J_sc by 1 mA/cm² and V_oc by 10 mV due to better response in infrared spectrum. The best conversion efficiency of back point contact solar cells fabricated with standard industrial emitter and backside passivation is 19.35%.