Light‐induced degradation and regeneration of multicrystalline silicon Al‐BSF and PERC solar cells

Abstract

Light‐induced degradation (LID) is a well‐known problem faced by p‐type Czochralski (Cz) monocrystalline silicon (mono‐Si) wafer solar cells. In mono‐Si material, the physical mechanism has been traced to the formation of recombination active boron‐oxygen (B–O) complexes, which can be permanently deactivated through a regeneration process. In recent years, LID has also been identified to be a significant problem for multicrystalline silicon (multi‐Si) wafer solar cells, but the exact physical mechanism is still unknown. In this work, we study the effect of LID in two different solar cell structures, aluminium back‐surface‐field (Al‐BSF) and aluminium local back‐surface‐field (Al‐LBSF or PERC (passivated emitter and rear cell)) multi‐Si solar cells. The large‐area (156 mm × 156 mm) multi‐Si solar cells are light soaked under constant 1‐sun illumination at elevated temperatures of 90 °C. Our study shows that, in general, PERC multi‐Si solar cells degrade faster and to a greater extent than Al‐BSF multi‐Si solar cells. The total degradation and regeneration can occur within ∼320 hours for PERC cells and within ∼200 hours for Al‐BSF cells, which is much faster than the timescales previously reported for PERC cells. An important finding of this work is that Al‐BSF solar cells can also achieve almost complete regeneration, which has not been reported before. The maximum degradation in Al‐BSF cells is shown to reduce from 2% (relative) to an average of 1.5% (relative) with heavier phosphorus diffusion.

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

“…The reduction in IQE is the strongest in the ~850 to 1100‐nm wavelength range, which indicates that the degradation occurs in the bulk or at the rear surface. Consistently, earlier studies have suggested that LeTID is mainly a bulk effect . Interestingly, both surface passivation schemes produce nearly identical IQE spectra also in the short wavelength range (both before and after degradation), although it is generally understood that AlO x is unfavorable for phosphorus emitter passivation due to the high density of negative fixed charges in the thin film .…”

“…Thus, the reduced LeTID could be at least partly explained by a heavier phosphorus emitter, and hence enhanced gettering, in the b-Si cells, 6 although the defect responsible for the degradation is likely another impurity than Fe. 40,41 This explanation supports the conclusion that LeTID is a bulk effect, as suggested previously, 12,23,24 instead of, eg, deterioration of rear surface passivation.…”

“…Consistently, earlier studies have suggested that LeTID is mainly a bulk effect. 12,23,24 Interestingly, both surface passivation schemes produce nearly identical IQE spectra also in the short wavelength range (both before and after degradation), although it is generally understood that AlO x is unfavorable for phosphorus emitter passivation due to the high density of negative fixed charges in the thin film. 19,25,26 The charge polarity was indeed confirmed to be negative, and hence, surface passivation is attributed to excellent chemical passivation provided by ALD AlO x.…”

Design Criteria for Micro-Optical Tandem Luminescent Solar Concentrators

“…Table 1 shows the comparison between best-case scenarios of the mirrorless and perfect-mirror configuration, for unity and 0.98 PLQY. Additionally, Table 1 compares the overall power output with the use of a 25.6% cell efficiency, silicon heterojunction structure with interdigitated back contacts as the subcell [37]; we also demonstrate the power output possible with this tandem LSC-Si architecture by replacing the subcell with a passivated emitter and rear contact (PERC) Si cell [38].…”

Optimization of Belt Furnace Anneal to Reduce Light and Elevated Temperature Induced Degradation of Effective Carrier Lifetime of P‐Type Multicrystalline Silicon Wafers

“…The degradation phase in mc‐Si cells is followed by a regeneration phase. Regeneration has been reported for both PERC and Al‐BSF (aluminium back surface field) solar cells at time scales of about 320 h and 200 h, respectively, under 1‐sun illumination at 90 °C device temperature . However, such long time scales may cause a significant energy yield loss (kWh) in fielded PV modules.…”