Lifetime degradation and regeneration in multicrystalline silicon under illumination at elevated temperature

Abstract

We examine the carrier lifetime evolution of block-cast multicrystalline silicon (mc-Si) wafers under illumination (100 mW/cm2) at elevated temperature (75°C). Samples are treated with different process steps typically applied in industrial solar cell production. We observe a pronounced degradation in lifetime after rapid thermal annealing (RTA) at 900°C. However, we detect only a weak lifetime instability in mc-Si wafers which are RTA-treated at 650°C. After completion of the degradation, the lifetime is observed to recover and finally reaches carrier lifetimes comparable to the initial state. To explain the observed lifetime evolution, we suggest a defect model, where metal precipitates in the mc-Si bulk dissolve during the RTA treatment.

Impact of black silicon on light‐ and elevated temperature‐induced degradation in industrial passivated emitter and rear cells

“…Nevertheless, the largest degradation is observed in the non‐textured edges of the SiN x ‐passivated b‐Si cells, which is an interesting finding and will be discussed later in more detail. Finally, Figure C reveals that the degradation is rather uniform laterally in good grain areas, which is characteristic of LeTID . However, defect clusters show slightly stronger LeTID, as reported recently, which is even more pronounced in the acidic‐textured cells (Figure E,F).…”

Cu gettering by phosphorus-doped emitters in p-type silicon: Effect on light-induced degradation

“…24, we find an average Cu concentration of ∼7 × 10 13 cm 3 in the reference samples with no emitter, which approximately corresponds to the Cu contamination levels reported by several authors in as-cut solar-grade wafers. 1,12,25 In Group A, the residual Cu concentration after gettering is estimated to be ∼3.8 ×10 13 cm 3 (i.e. a gettering efficiency < 50%).…”

Impact of Extended Contact Cofiring on Multicrystalline Silicon Solar Cell Parameters

“…It is known that high temperature steps during cell processing are influencing the strength of this degradation, and that they can be minimized by an effective external gettering [26]. It could also be shown that the firing step has a strong influence on LeTID strength, and that it can be minimized by applying a co-firing step at lower temperature [27], [28]. Recently, it could be demonstrated that an additional second firing step at lower peak temperature can significantly reduce the LeTID strength, and it was pointed out that although LeTID can be reduced, cell efficiency (series resistance) might be affected by this second lower temperature firing step [29].…”