Manifestation of Light- and Elevated-Temperature-Induced Degradation in n-Type Silicon: Initial Lifetime Improvement Due to Temporary Recovery

Light- and elevated-temperature-induced degradation (LeTID) has been the most discussed degradation phenomenon during the late p-type passivated emitter and rear cell (PERC) era. It is important to investigate whether similar issues affect the new generation of n-type tunnel oxide passivating contacts (TOPCon) solar cells. This study focuses on the temporary recovery (TR), the reverse reaction to the degradation reaction. TR has been key to understanding LeTID in p-type Si. Its existence is demonstrated and reported in n-type silicon solar cells for the first time. Further, the repeatability of the degradation-TR-cycle is shown and other effects unique to TR are demonstrated, such as a negative activation energy, and the TR rate constant scaling superlinearly with Δn. With TR as a tool, LeTID defects are identified to be present already after the fast-firing process. Such defects, if initially present, can have a multitude of effects. First, they lower the initial efficiency. Second, this might lead to the development of processes that are indirectly based on TR, enhancing the efficiency but concurrently leading to stronger degradation. Furthermore, it is imperative to exercise caution and to include the potential for TR when devising stability tests. Finally, it is demonstrated that strategies to mitigate LeTID in p-type also work for n-type.