Rapid‐Thermal‐Annealing‐Induced Passivation Degradation and Recovery of Polysilicon Passivated Contact with Czochralski and Cast Multicrystalline Silicon Substrates

Abstract

Metallization of high‐efficiency n‐type solar cells with tunnel oxide passivated contact (TOPCon) structures often requires a high‐temperature rapid‐thermal‐annealing (RTA) process, which potentially induces a notable degradation of device performance. Herein, the RTA‐induced passivation degradation mechanisms and potential recovery processes are clarified by postthermal annealing or hydrogenation based on both Czochralski (Cz) silicon and cast‐multicrystalline (cast‐mc) silicon wafers. It is found that the RTA process induces at least two kinds of defects, i.e., thermal‐quenching‐induced defects and hydrogen‐release‐induced defects. The passivation quality can be partially recovered under a high‐temperature annealing at 820 °C, which, however, can be fully restored via a postmoisture/nitrogen hydrogenation treatment at 450 °C. In general, the two mentioned wafers, i.e., n‐type Cz c‐Si and cast‐mc silicon substrates, demonstrate similar passivation behaviors in most cases before and after RTA treatment. Finally, it is inferred that the inferior passivation properties of the n‐type cast‐mc silicon samples are related to the relatively low bulk quality. This can be confirmed by the fact that samples with n‐type cast‐mc Si substrates show an abnormal passivation behavior with highly effective lifetimes in the low‐density carrier region, suggesting the existence of electron trapping states.