Experimental Investigation of the Impact of Iron Contamination and Gettering on Polysilicon/Oxide Based Solar Cells

The passivating contacts based on polysilicon/oxide (commonly known as TOPCon) has emerged as the next generation high-efficiency silicon solar cell technology. Besides its excellent passivation and carrier selectivity, polysilicon/oxide structure also exhibits strong impurity gettering effects. However, it is not entirely clear how bulk iron contamination and subsequent gettering would affect the polysilicon/oxide based solar cells. In this work, we experimentally compared and assessed the impact of iron gettering on the polysilicon/oxide passivation quality and firing stability. Subsequently, polysilicon/oxide cells with different initial bulk iron concentrations were fabricated and analyzed. Results show that the polysilicon/oxide structure is unaffected by iron gettering, while the boron doped emitter degrades due to the accumulation of iron (i.e. gettering). Together with the remaining bulk Fe contamination (if gettering is insufficient for a high iron content), the degraded boron doped emitter can degrade both the open-circuit voltage and short-circuit current. Meanwhile, an increased ideality factor is observed with increasing initial bulk iron concentrations, exhibiting a reduced fill factor. In addition, the cells with a higher iron contamination is found to be more temperature sensitive.