Review of light-induced degradation in crystalline silicon solar cells

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

“…As the Cu-related degradation rate is proportional to the Cu concentration involved in the LID process, 6,26 Figure 3 further supports the conclusion drawn from the results presented above, i.e. the gettering anneal followed by air-cooling resulted in partial, yet incomplete removal of bulk Cu impurities.…”

“…Outside the intentionally contaminated regions, the average diffusion length was also found to decrease from ∼600 µm up to ∼425 µm, probably due to the light-activation of the so-called boron-oxygen complex. 6 In order to quantitatively estimate the bulk Cu concentrations before and after gettering, it is possible to leverage earlier studies where the strength of the Cu-LID process (i.e. the lifetime/diffusion length variation before and after light soaking) has been correlated to quantitative measurements of the interstitial Cu concentrations involved in the degradation process.…”

“…The presence of parasitic Cu contamination is known to progressively deteriorate the bulk minority carrier lifetime during exposure to illumination. 6 This phenomenon is referred in literature to as copper-related light-induced degradation (Cu-LID) and recent root-cause investigations have proven that Cu-LID arises from the transformation of interstitial Cu atoms into highly recombination active precipitates in the bulk region of the wafer. [7][8][9][10] Gettering is a well-established technique, by which transition metal impurities are relocated to pre-defined substrate areas where they result less harmful for the device performance.…”

Recombination activity of light-activated copper defects in p-type silicon studied by injection- and temperature-dependent lifetime spectroscopy

“…Despite the slight shift between s init and s ref , which is probably caused by the effect of the contamination procedure on surface and Auger recombination, the superposition of the lifetime curves obtained from these two methods indicates that both of them can be used to determine the actual Cu-related lifetime. Since the latter approach would require the accurate measurement of s init at varying temperatures, which may turn interstitial copper into a recombination active state before light soaking, 9,13,24 in this work, s Cu has been calculated by compensating the lifetime measured after degradation with temperature-dependent lifetime data obtained from a separate non-contaminated reference specimen.…”

“…14,30 However, this reaction does not explain the aforementioned decrease of Cu þ i concentration during light-soaking. Moreover, DLTS studies on intentionally Cu contaminated material revealed the existence of two acceptor energy states located at E v þ 0:41…0:45 eV [31][32][33][34] and E c À 0:16 eV 24 and a donor energy level at E v þ 0:22 eV, 24,35 which were later associated with the substitutional copper defect. 35 While the energy state at E c À 0:16 eV seems to be in good agreement with LS results reported in this study, no strong evidence of the other energy states can be found.…”